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wayneh
05-14-2012, 03:54 PM
I'm trying to repair my daughter's RCA television, and I need advice about choosing a replacement MOSFET. I've just ordered a 2SK2917 (http://www.semicon.toshiba.co.jp/docs/datasheet/en/Transistor/2SK2917_en_datasheet_090929.pdf) from Mouser to replace the 2SK2842 (http://www.google.com/url?sa=t&rct=j&q=2sk2842&source=web&cd=2&ved=0CIUBEBYwAQ&url=http%3A%2F%2Fwww.semicon.toshiba.co.jp%2Fopenb 2b%2Fdocget.jsp%3Ftype%3Dwatermark%26pid%3D2SK2842 %26lang%3Den%26path%3D2SK%252F2SK2842_en_wm_200909 29.pdf&ei=GCmxT6DULIqi8gTxwYSUCQ&usg=AFQjCNGAX6XpsAlqITzW22w8xE_x1trFzw&sig2=2RiviTL3FezV68axKtEDzA) I pulled from the power supply. The current ratings are higher for the 2917, but my concern is the higher (but still small?) capacitance and inductance of this "larger" MOSFET. Will this be a problem?

FWIW, the 2842 I pulled from the board has higher current ratings than the 2SK2543 shown on the attached schematic. Probably means they knew this was under-specified?

http://forum.allaboutcircuits.com/attachment.php?attachmentid=42888&d=1337010801

I was lucky to find this schematic online, along with training materials, a troubleshooting guide and so on. It was soon obvious that the power supply is dead, and I removed TP020 (left side middle of schematic), the switching MOSFET for the transformer primary coil. It tested dead short. The info I found suggests replacing all the active components on the primary side if you find the MOSFET dead, so I've ordered all of the transistors and zeners. All cheap compared to the MOSFET.

mcasale
05-14-2012, 04:21 PM
Interesting schematic. I'm not familiar with some of the component designators. Is LP020 an inductor or ferrite thing? I wonder if it's supposed to help diminish ringing.

Looking at the spec sheets, it seems these parts are pretty close, except for the gate capacitance. It seems like the swap is worth a try. You may want to drop the value of the gate resistor, RP021, to compensate for the higher capacitance. Are these passive parts through-hole or surface-mount?

wayneh
05-14-2012, 05:04 PM
Thankfully, the parts are all thru-hole. I'd have probably given up already if they weren't.

Good point on the gate resistor. I could just piggyback another resistor in parallel. But without a scope, I'm not sure how I'd detect any change. :(

I'll look at LP020 to see if I can identify it. It must be an inductor of some kind.

So, you're not terribly concerned that the new MOSFET will not work?

mcasale
05-14-2012, 05:24 PM
The time constant on the gate is less than 80nSec typically. Hard to tell if it's significant.

Otherwise, I'd say full steam ahead. Let out the magic smoke!!!

Good luck.

wayneh
05-14-2012, 05:37 PM
Let out the magic smoke!!!Ha, thanks. That'd be more fun if it wasn't a $5 MOSFET :eek:, plus a comparable shipping fee.

Those waveforms show "T = 12S". Does "T" refer to a single cycle (meaning = 83.3kHz) or is it the entire x-axis ( = 250kHz)? Either way, it seems that 80ns is "small" by comparison?

mcasale
05-14-2012, 05:55 PM
My guess is that T=12uS is the period of the pulse. So, 80nS is small compared to that, but you still want the edges to be as fast as possible to minimize time in the linear region and self-heating.

Looking at the schematic again, I notice the gate resistor is NOT driven by a low impedance. During pull-up it is driven through RP023 and RP027, which is 1.1K (if I'm reading it correctly. That gives an overall time constant of about 3uSec. That's probably why the gate voltage looks squirrelly. So it looks like turn-on is the slowest time.

The turn-off current goes through the emitter of TO023, which should be a much lower impedance, I THINK.

I wonder why they didn't use a rail-to-rail driver, with all these discrete parts.

Still, I guess it still works, even if the FET gets a bit warmer than it should.

wayneh
05-14-2012, 05:59 PM
Still, I guess it still works, even if the FET gets a bit warmer than it should.It's held against a large piece of aluminum (with thermal paste) by a spring clip, so I guess they designed for that. Since the replacement is much larger (lower Rds) than the original design, I'm hopeful. We'll see.

crutschow
05-14-2012, 08:49 PM
After it runs 15 minutes with the new transistor, unplug the TV and see how warm it is. If not too hot to hold a finger on it, then it is probably OK

BSomer
05-14-2012, 09:03 PM
I'm guessing this is a little late... According to a cross-reference sheet I have, ST makes a "direct replacement" for the 2SK2842. It is the STP11NK50ZFP and is roughly $2.50 @ Mouser.

http://www.datasheetcatalog.org/datasheets2/59/599765_1.pdf

wayneh
05-14-2012, 09:14 PM
I'm guessing this is a little late...Yes, but thanks. I really should have looked at cross references before I ordered. Duh. I was even able to find the original part from other sources, but wanted to order everything from one place. So I just used Mouser's filters and ended up where I did.

debe
05-14-2012, 09:42 PM
With SMPS replace all the electrolytic capacitors. Un less you have am ESR meter to check them. Also make sure CP008, the mains filter cap is good. Also check RP006 & 007 120K resistors as they kick start the powersupply at turn on

wayneh
05-14-2012, 09:55 PM
With SMPS replace all the electrolytic capacitors. Un less you have am ESR meter to check them. Can they be checked this way on the PCB? I didn't think to order replacements.
Also make sure CP008, the mains filter cap is good. I can confirm it holds a helluva charge, since I purposely shorted it before working on the MOSFET. Yikes! :eek: Won't do that again.
Also check RP006 & 007 120K resistors as they kick start the powersupply at turn on Good point, and an easy test.

BSomer
05-15-2012, 05:18 AM
Can they be checked this way on the PCB? I didn't think to order replacements.

I have seen some home made ESR testers that can supposedly check a capacitor in circuit. For instance, from one of our very own members w2aew...

http://www.youtube.com/watch?v=bmYAgat-sOQ&feature=g-user-c

wayneh
05-18-2012, 04:37 PM
I'm looking for advice on where to go next.

Spent yesterday afternoon replacing all primary side transistors and diodes (other than the bridge, which is working). TV set is still dead :confused: but the power supply is now buzzing :D.

The MOSFET replacement was the wrong size! Can't believe I didn't check for that but anyway it installed easily with just a little bending of the leads. Was surprised and very glad the larger pins still fit the PCB holes, and that there was room on the heat sink. Whew!

The bridge is supplying about 174V for "RAW B+", and the oscillator seems to be working as judged by the buzz that starts a second after plugging in the set. But there's essentially nothing going thru the transformer on either side. I'm seeing no more than 1V anywhere on the secondary side.

My to-do list. Please help add things to look at!
I previously replaced RP020 (current sense power resistor) and will check it again next time.
Will check RP006 and 7 as suggested by debe.
Will look for voltages on top of CP024 and 25, and CP040. This doesn't really test them, but might be interesting. I'll first test caps for shorts with power off.
Looking hard at opto-isolator IP001, which provides feedback from the secondary back to the primary. According to the pdf, it must light up to draw more power thru the secondary. If it burnt out, I think it produce my dead-set symptom?
42994

THE_RB
05-20-2012, 09:44 PM
It's common to have a secondary side short that originally killed the PSU. Check the horiz out transistor (big transistor that drives the HV flyback transformer). It is likely shorted which is bringing down the secondary rail.

In the old days it was easy enough to disconnect the secondary side after the diode rectifier and connect a 100w light bulb etc as a load, and run the PSU and check it is regulating and producing the right voltage 120v DC. These days the PSUs are smarter and have standby systems and feedback systems so it's not always possible to run the PSU by itself on more modern sets.

A test you can do on the secondary is check it for shorts, ie attach a DC PSU after the diode and see if the voltage comes up ok or drags your DC PSU down into current limiting. You don't need a 120v supply, even a 20v or 30v supply will be fine for that test.

wayneh
05-20-2012, 10:45 PM
It is likely shorted which is bringing down the secondary rail.I'll look into this. But for my own understanding, wouldn't this cause a lot of current to flow on the primary side? I'm not seeing any. There is about 174V on top of the main filter cap and the primary coil, and only maybe 3V on the bottom (the rest across the MOSFET I just replaced).

Hmmm... Maybe the voltage drop across the current sense resistor is turning it all off?

Anyway, thanks for the tip.

R!f@@
05-21-2012, 12:12 AM
My my !! Quite a predicament.

dataman19
05-21-2012, 06:53 AM
Have you eliminated the flyback?
Sounds like you could have a bad flyback (the buzzing)..
Incidentally, this is a switching regulator to drive the flyback transformer.
There are numerous issues and several suspects that need to be eliminated.
..
Question: Was the original MOSFET actually bad?
...
The pulses coming from TP020 are the switching pulses to drive TP023 and TP025. The 600v pp waveforms going in to TP020 are the Horizontal Blanking signals and also the switching regulator sync.
..
I would suspect the buzzing sound to be the flyback switcher either running off frequency (TP020 is wrong) or a bad flyback.
...
Do you have a High Voltage Probe to check the aquadag voltage (the lead coming off the side of the CRT)??? How far off spec is it?
...
By the way, by "dead" do you mean no picture? If so is the neck of the CRT lit?
....
A lot of people get bogged down with the High Voltage issues, only to find out that the horizontal burst info is missing (which means you won't have high voltage).
...
Most flyback power supplies have a tickler/regulator winding and a DC blocking cap to allow the AC to ground (which essentially keeps the chroma burst from affecting the high voltage) CP009 (right above and to the left of TP020) - check this component as well (it's cheap, so just replace it).
..
Dave
Phoenix, AZ

sheldons
05-21-2012, 11:36 AM
iv repaired a few of these .....you need to change the opto as well....its a good idea to check all resistors and capacitors etc to do with the regulation/feedback side of this circuit as a problem here will lead to instant destruction of your new fet etc....

wayneh
05-21-2012, 03:39 PM
By the way, by "dead" do you mean no picture? If so is the neck of the CRT lit?Dead means nothing happens when you hit the power button. The buzz appears shortly after plugging it in, but that's the only sign of life.
Question: Was the original MOSFET actually bad?Unknown. The set was dead but buzzing when I started all this. One of the first troubleshooting tests is to check the voltage on the gate (currently less than 0.5V). I screwed up and touched something else also and shorted it out. Then it was certainly dead, and not buzzing anymore either. :eek:
Have you eliminated the flyback?
Sounds like you could have a bad flyback (the buzzing)..No, I haven't looked at this. Is this relevant to a power-off set?
Do you have a High Voltage Probe to check the aquadag voltage (the lead coming off the side of the CRT)??? Nope.
CP009 (right above and to the left of TP020) - check this component as well (it's cheap, so just replace it). Will do.
Thanks for your insights. I'll keep posting my findings. I really don't want this thing to beat me.

wayneh
05-21-2012, 05:52 PM
A test you can do on the secondary is check it for shorts...The "cold" (not mains connected, see photo) side of the power supply appears to have jumpers on all the outputs. It would be fairly easy to just snip or desolder one end of these, one by one, to see if opening a loop allows the other voltages to come up. A repair would then also be very easy. Does that plan make sense?

I guess I'd start with the 126v loop (jumper JP065, upper right) since the others are fused, and all those fuses are still good.

http://forum.allaboutcircuits.com/attachment.php?attachmentid=43043&d=1337622713

debe
05-21-2012, 10:25 PM
Jp065 is a good place to start. If it fires up I would suspect the Horz output transistor. An ohms test on these transistors is not always conclusive, as iv had transistors that are leaky & test ok with an ohms test & lock on when the hv is fed to them. Its easier to replace a suspect faulty transistor.

THE_RB
05-22-2012, 11:04 AM
The "cold" (not mains connected, see photo) side of the power supply appears to have jumpers on all the outputs. It would be fairly easy to just snip or desolder one end of these, one by one, to see if opening a loop allows the other voltages to come up. A repair would then also be very easy. Does that plan make sense?
...

With newer sets they will shutdown the PSU on many types of fault, basically if you start disconnecting things there is no guarantee the PSU will come up ok as it might detect things are not working and shut down. The fault you describe after your repair is normally called "hiccupping" and is a symptom that the PSU is faulty itself or has detected some other issue that may include over/undercurrent, over/undervoltage on the outputs.

As debe said test or replace the horiz out transistor, (I mentioned it before) but before I did that I would just connect a 30v 1A (or 0.5A) limited DC PSU on that cap on the 126v rail. If it rises to 30v ok you can be fairly sure there is not a major short there, and the test takes seconds and won't hurt anything.

On new sets the amount of feedback can be troublesome, it's not uncommon for the flyback to generate a DC voltage signal that feeds back to the main PSU, so if the PSU and flyback are both not perfect then it will shut down the PSU. You can do a lot of tail-chasing on sets like that!

wayneh
05-22-2012, 03:17 PM
OK, I'll try that on all the secondary side loops, after the diodes, starting with the horizontal. I was thinking I didn't have a suitable power source but I actually built a variable voltage, current-limited power supply years ago that will work nicely for this.

Tail chasing is definitely a problem, but I believe the only feedback from the secondary to the primary is via the optoisolator OR an overcurrent condition seen on the current-sense resistor on the primary.

R!f@@
05-22-2012, 07:02 PM
There is a simple approach to this.

There is a way to test if the MOSFET drive is correct or not with a DMM.

I repair this daily.

Care to listen to me.

If so tell me the status of the Voltage at Source of MOSFET after removing it. u NEED TO APPLY POWER AFTER REMOVING THE POWER MOSFET.

Measure the DC voltage and AC voltage at the course and the positive of the filter cap. The filter negative should be DMM common negative point.

If you get around 300V DC with No AC voltage what so ever U are good with only if u don't have a an Active PFC circuit. If u have an active PFC then u should get a DC close to 400VDC.

The if the above measurements are correct then switch of, dicscharge all the caps in the primary side. Connect DMM at around 10V range DC. Negative to filter negative, positive to gate pin of MOSFET, with MOSFET still removed.
Apply power as u keep an eye on the meter. The meter will show around 2 to 4V DC and a little more if u switch it to AC.

Post back. U will find the fault pretty quick

Plus post the complete schema so I can study it.

wayneh
05-22-2012, 07:38 PM
I've been testing and just now found your post. Here's the entire schematic.
43073
And the training guide
43074

Here are my latest results, which I think are getting me to the answer!

• RP006 and 7, the startup resistors tested good.
• CP024 AND 25 had about 6V across them, after being unplugged a few days. So one could be open but neither is shorted.
• CP040 had no voltage but there is a path to ground, so no surprise. No measurable resistance, so not shorted.
• CP008 and 9 both have >120V on them after several days, so again one could be open but neither is shorted.
• Applying 20V to JP065 - an easy-access jumper on the supply to the horizontal transistor - took my power supply down to under 1 volt at over 1A, maybe 2A. !!!!! :) That's very suspicious, right?

Many posts I've found online suggested replacing the horizontal transistor to fix a set that is buzzing but otherwise dead. So I'm proceeding right now to remove that whopper transistor, TL035 in the schematic.

R!f@@
05-22-2012, 07:55 PM
gimme a miniute to check

No need to remove the HOUT. Just check for dead short between CE. IF u don't get zero ohms then it is OK>

wayneh
05-22-2012, 08:04 PM
It's dead, and it's a S2055N. I pulled and tested it with an LED and a 9V battery. The LED lights even when the base is grounded!

R!f@@
05-22-2012, 08:09 PM
H out can only be tested in one way that is with DMM in diode check mode.
Positive to collector. CE should be open, CB should be open. If u get this results than it is OK

wayneh
05-22-2012, 08:13 PM
CE is dead short. CB is 38Ω. Das ist kaput!

R!f@@
05-22-2012, 08:14 PM
Ahh then it is indeed kaput, but u still can fix the PSU. if it is faulty u know.

Check to see the supply is working or not ?

R!f@@
05-22-2012, 08:21 PM
With HOUT removed it's totally safe to run the set. U should get the stated voltage at collector if the supply is OK.
And around 5 to 10VAC at base if the Y/C is producing the H. Pulse

wayneh
05-22-2012, 08:53 PM
Hmmm.... I was able to get the set to briefly power on now. An AC voltage of 21V appeared on pins 16 and 18 of LP003, where the high voltage is produced. The set quickly powers down and I hear various clicking sounds, like a relay click. There is specified voltage 132V on the horizontal supply cap (CP080) though. :)

I'm not discouraged, as I think what I'm seeing now is the result of feedback regulation.

R!f@@
05-22-2012, 09:02 PM
The set will go to standby indicating a horizontal fault since there is no Hout.
The μC will monitor the H.Fly back pulse.

U can measure the PSU stated output voltages at switch on. Just keep pressing the remote stby button. U can keep the PSU cycling.
If u get the stated voltages then PSU is OK.

Just replace the Hout. Any Hout with a damper will suffice if it is rated above the s2055 Ic

wayneh
05-23-2012, 01:13 AM
Having trouble finding a replacement. The schematic shows ST1803DHI (http://www.datasheetcatalog.org/datasheet/stmicroelectronics/5950.pdf) (10A 50W 20Ω base-emitter resistor), while the one I pulled was a S2055N (http://www.audiolabga.com/pdf/S2055N.pdf) (8A 50W 50Ω resistor). Of course there are lots of other specs.

NTE shows NTE2636 (8A 50W) as a replacement but it's not readily available either. NTE 238 (8A 100W) sounds good but is maybe overkill and pricey.

Anyway, any suggestions?

R!f@@
05-23-2012, 05:57 AM
What about BU508DF (http://pdf1.alldatasheet.com/datasheet-pdf/view/17003/PHILIPS/BU508DF.html)

Trust me, BU508DF is a good replacement and I think it's cheap.

Now. don't worry about the base resistor.

But if u are having doubts just wire a 50 ohm 1W R across BE.

debe
05-23-2012, 11:04 AM
Neither transistor is all that expensive here in Australia ST1803DHI is $7.05. BU508DF is $3.23.

THE_RB
05-24-2012, 11:34 AM
BU508 are a good catch-all but will give problems in some sets especially newer ones. Any supplier that specialises in parts for TV repair should have stocks of the proper transistor.

Now after heaps of time repairing PSU and replacing Hout, you may find it's got a shorted flyback transformer. Testing those is whole new story. ;)

wayneh
05-24-2012, 01:41 PM
Yes, I can see why people just throw out sets rather than have them repaired. A fancy new set (ie. not a back breaking, power sucking, giant CRT) begins to look pretty good.

I found a local place that will order a NTE2636 for me, for $4. I have to wait, but no shipping charge. I live in an area with maybe 200k people, and this is the ONLY store in the area that would sell me one. Sad. Fingers crossed that this is the magic bullet.

Any useful testing I can/should do before powering it back up?

debe
05-24-2012, 10:58 PM
This is what ive used for the last 35Yrs for testing LOPT transformers for shorted turns.

THE_RB
05-25-2012, 08:35 AM
Sweet. Haha it's been a while since I've seen an old Philips KT2A/3A flyback unit. I loved those old sets, fantastic for plug n play repairing.

You could even unplug some boards on them and make them into a pure RGB monitor which were used in many video arcade machines in the '80s.

I have a shorted turns tester somewhere but we stopped using them in the later years and just kept stocks of new good flyback units for all the common sets. Because flyback prices came down so much it was easier to just replace the unit as both a test and repair.

wayneh
05-31-2012, 11:26 PM
Now after heaps of time repairing PSU and replacing Hout, you may find it's got a shorted flyback transformer. Testing those is whole new story. ;)You nailed it, still no joy. :mad:
Today I eagerly replaced my Hout transistor (S2055N, it was shorted) with a new NTE2636. I now have secondary side voltages on the power supply, but the set won't allow power on at all, as it did with Hout removed. The main computer is likely preventing it from coming on at all. I can hear a high pitched whine when I plug in the set.

So, the flyback may be shot. Am I chasing a lost cause, or should I start looking for a replacement transformer? It has a grey panel on it labeled Murata MHF318-19, but a Google on that didn't provide much.

[update]Found more markings: Orega 40348A-26 10809150, also A UPC sticker with TCE 70234. Not much luck actually finding one, except for HR8935 which is over $50. Getting a bad feeling about this project.
OK, found it here (http://www.electronix.com/rca-replacement-flyback-262342-p-20303.html) for <$20. No mention of a warranty.

R!f@@
06-01-2012, 04:44 PM
Don't give up yet.
Tell me, when do u hear the sound.

On standby ?
or when it is switched on from standby ?
i.e when the set tries to start the horizontal stage.

THE_RB
06-01-2012, 08:17 PM
I feel for you Wayneh, sometimes a set is just too much work to fix. I'm not saying to give up but at some point you need to consider that option. A pro may have already given up on that set but then they usually have lots of sets to fix and limited time to spend on each one. Fortunately you have lots of time and at least you have a manual. :)

There are a number of options, I used to have a dummy load which could possibly be used on the B+ rail to test the PSU section, provided the PSU can run with no flyback (as we discussed). Examining the schematic should give you a good idea of that. I also had a 120v DC supply which could be used to run the whole flyback stage (to replace the B+ PSU for testing) but again this is not possible on all sets, and your PSU seems to generate multiple voltages so that option is probably not available to you.

Unsoldering the flyback is not that hard but you will need a good strong sucker, braid is not usually good enough. If you unsolder the flyback it shoudl be possible to devise some tests.

In the meantime before you unsolder it maybe Rif@@ can suggest some live tests as he seems to have some experience with this particular set?

wayneh
06-02-2012, 05:04 AM
Tell me, when do u hear the sound.The sound starts almost instantly when the set is plugged in, and lasts until a few seconds after is unplugged. During that time, hitting the power switch does nothing. The sound is faint and is a sort of hissing buzz with a high pitch. A little like air being let out of a balloon. I should have tried to hear where it was coming from but I wanted to minimize the time plugged in.

The PSU appears to be working; I checked all the secondary circuits and found voltages at or near the expected values, including the 132V B+. If any value was out of range, it was on the low side, but close. For instance I think I found 10.5 volts on "V12", which should be 11V or more. This makes me wonder about the optocoupler, which tells the primary to kick in to increase the secondary voltages. But again, B+ was on the high side of its range (1322V, I think).

wayneh
06-02-2012, 05:14 AM
I feel for you Wayneh, sometimes a set is just too much work to fix. I'm not saying to give up but at some point you need to consider that option. It's the ignorance that's so frustrating. If I knew a $20 transformer would get it going, I wouldn't flinch. But putting one in and still having a dead set would make me crazy.

From what I can read online, it sounds like these RCA sets (ITC008 chassis) are notorious for eating flyback transformers. It's a common failure mode and probably the root cause for the HOT shorting out. But replacing it is not like putting in a new fuse.

The ring testers are interesting, but cost more than the transformer. It'd be great if I could borrow one locally but that's not likely. So I'm working blind.

R!f@@
06-02-2012, 06:10 AM
U know u haven't read much.

Tell me or better yet show me. Need to know if there is any wire coupling the FBT core to the PSU. I need to see the whole shcema or ur TV.

Pictures man..gimme some freakin pictures.

wayneh
06-02-2012, 02:53 PM
The full schematic and training guide were posted in #26.

THE_RB
06-02-2012, 05:18 PM
It's the ignorance that's so frustrating. If I knew a $20 transformer would get it going, I wouldn't flinch. But putting one in and still having a dead set would make me crazy.
...

Try doing that 4 or 5 times a day while at the same time customers are screaming at you about why their TV is not fixed yet or why it costs so much... ;)


From what I can read online, it sounds like these RCA sets (ITC008 chassis) are notorious for eating flyback transformers. It's a common failure mode and probably the root cause for the HOT shorting out.
...

It's very common in small cheap sets, unfortunately replacing the flyback unit does not always guarantee a fix. Depending how the flyback blew it may have taken out other parts too.

I didn't check your schematic PDF but if there are waveforms shown for the base of the Hout transistor you could check there. As your PSU seems to be running if the Hout is being kicked repeatedly it's a good sign the set is ok but trying to start and can't start because of a blown flyback. If there is no activity at the base it *might* be because of other faults, but again on newer sets that have microcontrollers in charge you can't always tell as the micro might just try once and shutdown.

As an ex-pro if I was doing that set and wanted to spend the time to get it running I would have replaced the PSU parts (done), replaced the Hout (done) and then next up (given the symptoms you have posted) just replaced the flyback unit and crossed my fingers. :)

Another thing you could look for is a fault reference for that model TV, sometimes they publish a list of common faults and tell which parts to replace. Also sometimes the service department for that brand will actually talk to you on the phone if you are polite enough, and the technician there might offer some suggestions.

wayneh
06-02-2012, 07:25 PM
..then next up (given the symptoms you have posted) just replaced the flyback unit and crossed my fingers. :)That's where I'm at. I'm realizing that a ring tester, while they cost $50, could probably be made from parts I already I have, maybe just breadboarded in a few minutes. I'm thinking about it. The biggest "cost" would be testing it to convince myself it was working. I don't have a 'scope for looking at the waveform on the HOT. Sure would help.
Another thing you could look for is a fault reference for that model TV, sometimes they publish a list of common faults and tell which parts to replace. Also sometimes the service department for that brand will actually talk to you on the phone if you are polite enough, and the technician there might offer some suggestions.I did find an interesting post here (http://www.justanswer.com/tv-repair/2i89o-rca-model-36v430t-won-t-turn-on-when-plug.html) from someone with experience with this set.

R!f@@
06-03-2012, 06:43 AM
Assuming tht the supply is running with proper voltage in stby per ur posting.

The squealing u r hearing is probably because the PSU in not in sync with the horizontal stage.

In Most CRT's the supply will start and after tht the horizontal will too. With in μseconds the PSU will sync with horizontal and then goes to stand by and all is A OK. Now in ur case PSU starts but the horizontal does not resulting in PSU oscillation lower (15.625KHz) than the horizontal.

Resulting in audible oscillation with in the cores.

So I like u to look at the PDF attached of the hor stage.
Take a look a the HDRIVE path high lighted. Now u won't need a scope to do this, since I never touched a scope for trouble shooting any Hor related faults unless the Hout blows faster than U can say WTF happened.

But since u are beginner u might need an analog meter in the AC range at 10V. Now have the set plugged in but AC off. Meter probes need to be between GNDL ( negative probe).
First try at base of TL031.

Power off, meter on the base, ur eye on the scale. One hand holding probe, the other on power switch.

Switch on and see if the meter scale jumps to around a volt or two in the 10VAC range. If the set is in stby, u will need it to switch on with the remote or front control buttons.

Now there is a catch in this. If ur meter does not have a AC only connection ( where the meter in put has a cap to block the DC ) u are good. But if it does not the AC meter might be detecting DC. Now to make sure put the meter in DC 10V and try the test. The meter should never go above the 0.36VDC indicated in the schema. If it does, there is a problem in the HDRIVE signal or around that area ( may be a faulty tr).

Tell me if the DC is in range and the AC voltage stays at around a volt or two or the meter scale goes up and then goes to zero

wayneh
06-03-2012, 05:10 PM
Thanks for taking some time to lead me through this. The set is at my daughter's house (30 min drive one way, probably $8 in gas round trip!), so it will take some time before I can report results. The longer the chore list before I get there, the better. So if you can give a few of the next steps beyond probing the base of TL031, please do. Take for granted I'll probe the bases of TL032 and 33, maybe also TL061 and 62, by the procedure you've listed.

I get your strategy, to take a look at HDRIVE before committing to a new FBT. Makes good sense, except for the annoying cost of making multiple trips.

My meter is one of those cheap (free actually) Cen-Tech DMMs and has a 200V AC scale. It reads to 0.1V but does NOT block DC. Should I use a capacitor, say 0.1F, on the end of the probe?

R!f@@
06-03-2012, 07:31 PM
Yes....Use a 250V 0.1uf Cap to block DC, but do measure the DC par the diagram.


Next,. after power off, discharge the supply caps and in diode range check 'em driver transistors and the small coupling caps.

wayneh
06-03-2012, 08:31 PM
... in diode range check 'em driver transistors and the small coupling caps.Do you mean in-circuit testing?

For the caps, do mean to just look for shorts? There's nothing else I can check about them, so I suppose that's what you mean.

R!f@@
06-03-2012, 09:02 PM
Do you mean in-circuit testing?


For the caps, do mean to just look for shorts? There's nothing else I can check about them, so I suppose that's what you mean.

Yup..check 'em transistor junction for shorts.
But u need to desolder the cap to check.

If the caps are lower than the printed value, u are in for some cap swapping

radiohead
06-05-2012, 08:14 PM
I just had a tv die on me. It briefly turned on, then a horizontal line turned into a dot, then went away. Had no idea what it could be. My fix was buying a cheap flat screen tv to replace the old CRT one. Probably cost less than all the gas, time and parts. You can't put a price on the hands-on electronics training, though. Good luck.

R!f@@
06-05-2012, 10:07 PM
I just had a tv die on me. It briefly turned on, then a horizontal line turned into a dot, then went away. Had no idea what it could be. My fix was buying a cheap flat screen tv to replace the old CRT one. Probably cost less than all the gas, time and parts. You can't put a price on the hands-on electronics training, though. Good luck.

Horizontal line means ur vertical drive chip went to hell.

radiohead
06-06-2012, 12:41 PM
stupid question: how does a vertical drive chip create a horizontal line? You probably guessed by now that television sets are not my forte. You're my hero, R!f@@

wayneh
06-06-2012, 03:29 PM
Probably cost less than all the gas, time and parts.No question. You can also factor in the cheaper cost of operation.

About the only reason I'm continuing on this project is to encourage my daughter and new son-in-law - who want to live cheaply - that such things as self-reliance are necessary and possible with the right mindset. Assume you can fix anything and only give up when you have to. See what you learn along the way. If we can't fix this TV, they simply won't have one.

I get very disgusted with the majority of folks that'll pitch things to the trash just because they assume they cannot fix them. My neighbor - an engineer - buys a new lawn mower every time his air cleaner gets too plugged for the engine to run right. Or once when the throttle cable broke. Stunning.

R!f@@
06-06-2012, 03:57 PM
stupid question: how does a vertical drive chip create a horizontal line? You probably guessed by now that television sets are not my forte. You're my hero, R!f@@

Horizontal line results in Vertical scan failure.
Vertical means Up and down and up and down and it goes on. U know the electron beam the spot which glows the phosphor, so no vertical scan results in a single horizontal line...besides the vertical is the easiest part to fix ..!

Shall I go on ? :D

radiohead
06-06-2012, 06:09 PM
I'd love to pick your brain regarding TVs. They all operate pretty much the same, right? Like a radio has the RF amp, mixer, oscillator, 1st IF amp and so on, some may be more complex than others, but the block diagram will be pretty much the same...

debe
06-06-2012, 11:20 PM
Just a thaught, perhaps radiohead should start a seperate thread on his problems so it dont get confusing here.

R!f@@
06-07-2012, 11:26 AM
Wonder what OP is up to.

And yes TV consists of An input ( tuner, which some has inbuilt IF amp and others don't
), Tuner is responsible for picking up different channels in the LF,VF & UHF + some decent one has Cable band too & most recent has DVB capability.
Tuner has all the local oscillator and mixer and so an so forth.
Tuner is sometimes serviceable for me that is. And it is RF shielded resulting in a metal box thingy

Then comes IF for some, which separates the Audio and Video plus the Syn pulses for Vertical & horizontal + the color burst for color syncing.

Audio path takes it's route to it's DSP ( if any ) and power amp.
Video path is a lot more complex. Which has secam, NTSC & PAL color DSP's. Then goes to Video amp which boosts the low video to high voltage to drive the CRT cathodes.

The vertical sycn goes to it's vertical amp and to deflection coil.
Horizontal takes a bit more complex path. Horizontal is responsible for generating the very much needed Higher voltage anode supply and other necessary auxiliary supplies and the horizontal deflection too.

And everything is powered by a standard PSU to generate the necessary start up and +B voltage.

wayneh
06-07-2012, 03:41 PM
Wonder what OP is up to.Hah, yes, and you are not the first. As I said, the project is some distance away and I have many other distractions, so it will be a while. Spent the afternoon jetboating yesterday!

I discovered that an old breadboard project of mine is actually very similar to the commercial ring tester for inductors such as flybacks and yokes. So I'm going to try making one.

The idea is to generate a 2% duty cycle, 10Hz square wave. The brief pulse resets a counter and sends a small (20mA or so) current into the inductor under test (ie. flyback), in parallel to a capacitor. When the current is cut off, the resulting LC ringing is detected (above a threshold) and squared up, and the peaks counted. The higher the count, the better the inductor. I already had a timer, counter and op-amp on the board ready to go, so I'm almost there.

radiohead
06-07-2012, 05:12 PM
debe, That old tv is gone. There are no more issues with it. R.I.P., old TV

wayneh
07-16-2012, 11:17 PM
Finally back to it! Today I did some testing, all with power off and everything in-circuit. I could use some help (!!) understanding the results.

First, my DIY ring tester showed a full 10 rings (!!) on the LOPT primary (LL005 pins 1 & 5 or ground and 5). I got no more than 1 ring on every other pin pair combination. Inductor LL032/33 gave 6 rings (pins 1 and 3). The other side, pins 4 and 6 are tied ground and the base of the HOT, so no rings on that side.

The following transistor tests all used a cheap multimeter on the diode testing setting. I put the multimeter lead indicated on the transistor pin indicated and read the mV on the scale. As you can see in the table, I'm a bit lost interpreting all the tests. For instance, what happens with the bias resistors? I would have expected them to pull the mV very low, but I get "open" readings.
[update] Ah, just read that the results will usually appear "open". The meter current cannot overcome the bias resistor and the transistor doesn't turn on. Makes sense.

http://forum.allaboutcircuits.com/attachment.php?attachmentid=44558&d=1342548236

Here's the schematic again for the horizontal drive section under test.
http://forum.allaboutcircuits.com/attachment.php?attachmentid=44559&stc=1&d=1342548322

wayneh
07-18-2012, 02:59 PM
I need suggestions for my next move. Since the transistors are not obviously bad, not shorted at least, I'm tempted to start removing the LOPT. I'd disconnect the secondary connections first. The primary looks good with my ring tester, but I suppose these flyback transformers usually fail on the high voltage side?

nomurphy
07-18-2012, 04:27 PM
I've had to repair just about every TV that I've owned for various failures; GE, Motorola, Panasonic, Hitachi.

That hissing sound on older sets was typically caused by the internally shorted flyback.

DARWIN WARNING:
One thing that I was taught for testing the HV ouput, and have done on older units, is to put the tip of a screwdiver with a well-insulated handle under the plastic hood of the HV cable that goes to the CRT. If you get arcing to the tip then the HV is good (it is conducting through the high impedance screwdriver handle and you).

A less macho way of doing this is to remove the HV cable from the CRT, and tape it an inch or more away from some grounded metal with NOTHING else nearby -- briefly turn on the power.

The least macho way is to rent/buy an HV probe.

Oh, by the way, make sure you discharge the HV output before placing your fingers in the area.

wayneh
07-18-2012, 04:35 PM
Since my set won't power on, I really can't try that. I don't think there would be HV at the tube before the set powers on? Let me know if I'm wrong on that.

I am very suspicious of the flyback transformer. The primary appears good. Technically speaking, my ring tests of the secondary showed it's "bad", but I think that's inconclusive while it's still in-circuit. Since it's "only" about $25 to replace and I didn't find any obviously bad (to my eye) transistors, I may go ahead and just do that. It's just the thought of it NOT working afterwards that is holding me back. :(

nomurphy
07-18-2012, 07:14 PM
Since my set won't power on, I really can't try that. I don't think there would be HV at the tube before the set powers on? Let me know if I'm wrong on that.

You're probably correct regarding an older set; newer ones have the instant-on feature where the power button goes into a time-dilation pre-circuit and the power comes on just before you actually touch the button -- most people are not aware of this.

I thought you had fixed primary-side functionality, and were therefore considering issues with the flyback output??

It seems to me, that part of self-sufficiency is knowing when it is costing more to be stubborn than it is in just lettting go. However, if you're doing it for fun and a sense of accomplishment, then damn the torpedos and have at it.

wayneh
07-18-2012, 07:30 PM
Yeah, I'm pretty close to the end of the line with this set. But since the FBT is such a well known and documented cause of failure for this model, I'm reluctant to give up before I rule that out. I'd just like to a bit more sure before buying one.

You're correct, I do have the power supply working and have replaced the HOT. With the HOT removed, the set briefly powered on (front panel LED comes on) but then cycled off. I had PS voltages and hissing while "off" (no light). With the HOT in place, the front light never comes on. Should there be HV in the "off" state if the FBT is working? I'm a little reluctant to leave it plugged in very long while it's hissing.

nomurphy
07-18-2012, 07:47 PM
The FBT can store a charge, which is why one should always discharge the HV line before working on a TV with a CRT.

You could try disconnecting the HV line from the CRT (no external short or load), to see if that helps keep the primary-side running. But that may not work either, per other posters, if it's a set that incorporates certain aspects of fault-sensing.

wayneh
07-18-2012, 08:17 PM
...if it's a set that incorporates certain aspects of fault-sensing.It absolutely is.
With the power indicator off, but the set plugged in and hissing, would you expect HV on that big red cable? I'm not opposed to testing that as long as I can figure out how.

nomurphy
07-18-2012, 08:24 PM
No, I would not expect the horizontal or HV to be active with the TV off, or in standby mode.

You say the power indicator is off, but is the power actually off? If you haven't yet, try checking this. There were some TV's that used opto-isolator in the power on circuit -- typically these should fail to the off mode, but there maybe something else going on with yours.

wayneh
07-18-2012, 09:10 PM
You say the power indicator is off, but is the power actually off? If you haven't yet, try checking this. There were some TV's that used opto-isolator in the power on circuit -- typically these should fail to the off mode, but there maybe something else going on with yours.
Well, even when the power light is off, the PS is still on whenever it's plugged in, and B+ appears at the HOT. The PS is under regulation feedback via an optoisolator, which may have failed, though I don't think this would prevent power-up. I gather it's meant to compensate for a sag in voltage at the tube. It was suggested before that I replace it, but I haven't yet. My bad.

BTW, I posted the service training manual and schematic earlier in this thread in post #26 (http://forum.allaboutcircuits.com/showpost.php?p=488661&postcount=26). This might address any questions you have better than I can.

Nuts, just realized I forgot to look at the voltages on the base of Hout as R!f@@ had suggested a while back. I wanted to get all the unplugged testing done first and completely overlooked any hot testing.

R!f@@
07-19-2012, 07:13 AM
The Transistor readings does not make sense to me.

If you have done the voltage test I stated before, I could have known where ur fault lies wayneh.

I need you to go thru my post #51 and post ur results.

Voltage measurements tells fault area much faster than pulling out components to tst

wayneh
07-19-2012, 02:25 PM
The Transistor readings does not make sense to me.
Glad I'm not the only one.
I need you to go thru my post #51 and post ur results.Will do. It may be a couple weeks before I can get back.

R!f@@
07-19-2012, 07:06 PM
The transistor readings are not how it's suppose to be.

Any transistor without a R inside or not a darlington should not give any reverse reading in diode check mode. When checking CE, make sure the base is left alone. And any BC or BE reverse readings should show open readings from a DMM.

wayneh
08-08-2012, 09:35 PM
I need you to go thru my post #51 and post ur results.I've finally had a chance to complete this.

It wasn't very exciting: No AC or DC voltage on the base of TL031.

I used two meters jumpered together, one on the DC 2000mV scale and the other on the AC 200V scale. The black probe was jumpered to GNDL and the red probe held manually to the (tiny) base of TL031.

Helper #1 watched the meters while helper #2 plugged in the set. Up came the whine/hiss after a few seconds. No voltages on TL031. Hit the power button. No immediate effect. But a few seconds later, the power-on indicator light came on and the audio popped slightly. No voltages. Power light goes out seconds later. Repeat press of power button, exact same result. No voltages seen. Unplug. Hissing fades out seconds later.

Now what?

R!f@@
08-08-2012, 09:44 PM
My PC just gave me BSOD and restarted, and I was done writing. :mad:

OK. No H drive will give u a hissing sound from the PSU. As it will be running at a lower frequency.

The PSU will sync with in ms at power on to the horizontal stage..

So no H drive results in squealing.

Wayneh, can u measure the DC voltage levels marked on the schematic deflection page.
Cross check with the red numbers marked around the TL035, TL033, TL031, TL061, TL062 and 8VOS line, V12 line & +VSUPPLY line.

During the DC voltage measurements, if some voltages are missing try cutting power, wait for around 10s and power up. Keep the meter connected and ur eye on the scale. Like to know if the voltage spikes or not.

Come on MSN.. I am here..and if you are near the TV, it would be easy.

wayneh
08-08-2012, 11:25 PM
These data were all taken with the set plugged in but not "on".
8V 0.60
V12 10.56
+Vsupply 0.01
For the transistors, all bases and emitters were 0V. Collector voltages were
TL031 10.53
33 10.52
35 131.7
61 0.1
62 0

R!f@@
08-08-2012, 11:32 PM
8V 0.60


I don't understand this point. Shoooot ! got it. It's the 8V0S line giving 0V :D

V12 is OK..!

+VSUPPLY won't be there since set is not running.

Hmm.. This is getting some where..!

I believe u have a protect kicking in.

R!f@@
08-09-2012, 12:04 AM
Need to probe the 8V reg.

See the schematics power supply page, bottom left, u will find teh Reg IP030, a 9pin chip on a heat sink.

First check pin 2 for the 10.56VDC u got for the V12 line before.

If pin 2 does not have voltage then check fuse FZP30.
If pin 2 has the voltage, pin 1 should also shud be the same.

Next check pin 4. This pin will be activated if the set is turned ON from standby. Other wise I think it would be 0V.
If the pin is held LOW then the regulator will shut down.
I believe when the pin goes to around 3.3V the Reg will give output,
@ pin 8, which is the 8V Vcc.

If things get confused around there, check pin 6. see whether it is LOW or HIGH. Not in between.

And u might need to check the fuses in the secondary of the transformer too. All of em.

wayneh
08-09-2012, 06:07 PM
Attached are the details of testing last night under the direction R!f@@, with me and my son-in-law providing eyes and hands for local testing.

After reviewing the details, I believe most of the results are valid and the wheels came off only at the very last step, #8 in the attached. No surprise - late at night is when mistakes are made. I suppose we must have mistaken the labels on a couple of jumpers. I will resolve this at the next opportunity, in the bright light of day, before continuing on to other tests.

45253

vk6zgo
08-11-2012, 08:48 AM
I've had to repair just about every TV that I've owned for various failures; GE, Motorola, Panasonic, Hitachi.

That hissing sound on older sets was typically caused by the internally shorted flyback.

DARWIN WARNING:
One thing that I was taught for testing the HV ouput, and have done on older units, is to put the tip of a screwdiver with a well-insulated handle under the plastic hood of the HV cable that goes to the CRT. If you get arcing to the tip then the HV is good (it is conducting through the high impedance screwdriver handle and you).

A less macho way of doing this is to remove the HV cable from the CRT, and tape it an inch or more away from some grounded metal with NOTHING else nearby -- briefly turn on the power.

The least macho way is to rent/buy an HV probe.

Oh, by the way, make sure you discharge the HV output before placing your fingers in the area.

An even less macho method,which only works if you have hairy forearms,is to rest your forearm against the screen & turn the TV on.

If the tube is being fed EHT,the hairs on your arms will be attracted to the screen.
If they touch the screen,the charge is equalised,so you have to take the arm away for a second then repeat,when,if all is well,they will again be attracted.

This is quite sensitive,as it will even detect the very brief presence of EHT generated when you turn on a TV where the horizontal output transistor has a short from C to E.

R!f@@
08-12-2012, 11:48 PM
Wayn ! U did not list the V12 voltage. :mad:

No matter, Replace them CP094 & CP064. I believe they 1000μf. No ?

While u are at it. Check 'em all. That will make ur day. :D

wayneh
08-13-2012, 02:47 PM
U did not list the V12 voltage. :mad:
Nope. I carefully checked our chat log and we switched focus to the regulator immediately after I reported the 6V5 voltage, and you judged the C to be working. V12 would have been our next target.

Will look at those caps ASAP. ;)
Is there something in the data that makes you suspicious of them?

R!f@@
08-13-2012, 05:23 PM
Yaaaaaaaaaaaaaa!

Low Voltage !!

Need to even the odds.

wayneh
08-13-2012, 06:36 PM
Low Voltage !!Interesting. Way back in #45, I commented that "...I think I found 10.5 volts on "V12", which should be 11V or more. This makes me wonder about the optocoupler [IP001]..."

That measure of V12, which would have been taken with the set off but buzzing, matches up with the new data in the spreadsheet (row 10). I don't think it was taken while the power light was on, although I can't be sure. I didn't realize at that time that the set would go through 3 attempts to start up before stopping.

Anyway, should I still have an eye on that optocoupler or wait for testing/replacing those caps? If I have to order caps, I'll include the optocoupler either way. But I might have some caps on hand.

R!f@@
08-13-2012, 08:00 PM
Just find some to rule out the low capacitance theory

wayneh
09-25-2012, 07:38 PM
Finally I have replaced CP064 and CP094, the two 1000F electrolytic caps for the V12 and 6V5 supplies. I used new Panasonic low ESR 1200F caps.

I also replaced IP001, the optocoupler that feeds back to the power supply.

Alas, no joy. The voltages on the two supplies come up to 10.58v and 7.05V with the set plugged in but power light off. With the power light on, these fall to 7.06 and 5.41. It's tough to get a steady number, as the set cycles off pretty quickly.

V12 appears to have a problem. A clue perhaps?

I can see already that I should have also replaced CL035, another 1000F cap sitting on the V12 line in the deflection area.
[update] I used one of the old CP064 or CP094 1000F, 25V caps to replace CL035, which is a 1000F, 16v. No change. CL035, now removed, is not shorted or open and holds a charge.

R!f@@
09-25-2012, 08:46 PM
Still the same way ?

wayneh
09-25-2012, 09:07 PM
Yup. Dead set. The only news is the "discovery" of the big drop in V12 at attempting power-on. The voltage on CL035 is briefly higher than CL064 at power-on but equilibrates just as the set cycles off.

R!f@@
09-25-2012, 11:30 PM
Let me catch up..

wayneh
09-28-2012, 10:06 PM
I became suspicious of transformer LL033 (is it a choke?) but back in post #66 I noted that it gave a decent ring result on its primary, with my DIY tester. So the primary is not shorted or open. What else could be pulling V12 down? A problem with the supply itself, perhaps. I wonder if I could just inject a 12v power source instead of using the existing supply.

R!f@@
09-29-2012, 08:38 AM
u could inject a 12V but it should be isolated, but be careful about the current capacity needed by the TV.

Remember to switch on the 12V immediately after the TV.

Dodgydave
09-29-2012, 01:17 PM
Looking at the circuit on post #14, can you remove the 3 fuses on the secondary side, and disconnect the output from the +126V, so the psu is working with no loads, (i know the opto wont have a 13V supply to work) but will it work then, or have you done this already?

wayneh
09-29-2012, 04:07 PM
Looking at the circuit on post #14, can you remove the 3 fuses on the secondary side, and disconnect the output from the +126V, so the psu is working with no loads...That's a good idea.
In #26 I found that my Hout was likely shorted:
• Applying [external] 20V to JP065 - an easy-access jumper on the supply to the horizontal transistor - took my power supply down to under 1 volt at over 1A, maybe 2A. !!!!! That's very suspicious, right?

I confirmed this in #33; I reported seeing 132V on UB1 with the Hout transistor removed (it had failed to a short).

But I have not done the testing you just described. Since my problem appears to be with V12, I'm thinking of cutting jumper JP051 (easier than removing fuse FP061) first. I can check the voltage from the supply, as well as get an entry point for injecting external 12V.

wayneh
09-29-2012, 04:11 PM
... be careful about the current capacity needed by the TV.This could be a problem. My little supply can't get over 2A. I may need a car battery or such. I'd feel better about full isolation with something that doesn't plug in anyway.

R!f@@
09-29-2012, 04:15 PM
This could be a problem. My little supply can't get over 2A. I may need a car battery or such. I'd feel better about full isolation with something that doesn't plug in anyway.

Do not use a battery.!

wayneh
09-29-2012, 10:22 PM
You're concerned about inconsistent voltage?

R!f@@
09-30-2012, 04:46 AM
I am concerned about u having a short and the battery being what it is can supply enuf juice to fry some unwanted babies together with there tracks.

wayneh
10-01-2012, 01:04 AM
Got it. Well, the voltage only sags as it is. Seems like the short can't be too awful but your point is well taken. The fuse on V12 is over 3A, though. Not sure how I can supply more than 1 or 2A with my little LM317-based supply, without using a battery. Maybe 8-10 AAs would give enough juice without risking a crazy high current level.

THE_RB
10-01-2012, 04:44 AM
It's unlikely the 12v rail will need 2A! It's probably only used for the micro and some peripherals like sound and maybe AV switching. An LM317 will easily provide >1.2A and should be plenty.

Have you replaced the flyback transformer with a new (or known good) unit yet? That should have been about stage 3 of testing after replacing Hout tranny and some PSU parts. :)

wayneh
10-01-2012, 03:04 PM
It's unlikely the 12v rail will need 2A! It's probably only used for the micro and some peripherals like sound and maybe AV switching. An LM317 will easily provide >1.2A and should be plenty.Good to hear, I'll try that.
Have you replaced the flyback transformer with a new (or known good) unit yet? I have a part identified but I've been reluctant to buy it without a little more confidence that it will be the magic bullet. It's definitely a common failure mode of these sets. My inductor ring tester gave a good ringing on the primary of the FT, for whatever that's worth.

THE_RB
10-02-2012, 09:33 AM
I hear you. Flybacks cost about $35 and it can be disheartening to buy one and it doesn't save the TV set. It's not so bad if you are pro and will likely be fixing more of that same model TV, you end up with a big box of test flybacks, some new and some pulls.

Which probably leads to the repair methodolgy of swapping flybacks as a relatively easy test... Catch 22. ;)

I never bothered with a ring tester, but did have a shorted turns tester which I did not like much. Many of the faults that happen in flybacks are HV faults, where the flyback transformer might work ok if tested at 12v but at full voltage and power something arcs over in the windings. And other faults like an isolated winding being shorted to another winding would not be detected either by a shorted turns tester or ring tester.

I'm not advising you to buy a flyback, especially if it is going to cost $$$. Just that is what most TV guys would have done (or just junked the set and fixed other more profitable sets).

wayneh
01-04-2013, 09:36 PM
After a long hiatus I got back to this beast today.

To recap earlier work, it appeared that V12 was lower than specifications and this might have been preventing the set from starting.

Today I used an external power supply to inject 13.1V for the "V12". I did this by desoldering the power-supply (LP003 transformer) end of jumper JP051, and connecting the power supply to the jumper and ground.

The set did try to cycle on, briefly lighting the power-on LED, but did not start. :( Nuts, this was likely my last shot. The V12 voltage did not sag more than a few tenths at that time, staying well above 12 volts.

So the problem remains a mystery. Might be the flyback, but I'm not keen to pay to play without a more certain diagnosis.

R!f@@
01-04-2013, 11:42 PM
See if the Voltage at the Hout Collector sags when it tries to cycle on.
If it does then the FBT might be the culprit.

Or there may be a shorted component on the secondary of the fly back.

Just not go thru whole post, did you check all the diodes at the fly back secondary for shorts?

Did you sent me the whole schema before. ?

I meed to see the Y/C area to check for X-Ray protection.

wayneh
01-05-2013, 12:11 AM
Just not go thru whole post, did you check all the diodes at the fly back secondary for shorts?No, I don't think so.
Did you sent me the whole schema before. ?It's in #26.

One pain I'm having is that if the V12 falls, with the jumper open so I could inject 12 volts, the thing goes into over-voltage and shorts out the 27V zener DP027. I've gone through 2 of them now, once when I forgot to inject the 12v before plugging in the set and another when the test lead slipped off the jumper. Good thing I ordered several just in case. ;)

Anyway, I need to swap out the bad zener before I can try anything else. Done for today but could use a list of chores for next time.

sheldons
01-09-2013, 08:44 PM
regarding your lopt it is generally fairly easy to determine if it is faulty or not-easy way to check your power supply is behaving itself is to remove the feed to the line stage or remove your line op transistor so it cant drive the suspect lopt-with an oscilloscope (and isolation transformer) and a suitable lamp across your ht smoothing capacitor (i usually load it with a 40-60w lamp,depending what is to hand)......switch on and check your ht is correct and all your other secondary supplies...at this stage if you connect your scope to the line driver stage you can then check if your line osc is present and correct amplitude and frequency wise.
dont forget if you have a fault with the flyback tuning side of the line op stage either soldered joints or oc capacitors ,sc diodes etc your new lopt transistor and transformer may have a very short life. it might help as well to check all the line op derived supply rails for shorts too-field op stage etc....dont give up on the set just yet

wayneh
01-09-2013, 10:14 PM
...dont give up on the set just yetHa! Yes, it's getting very hard to continue spending more time on this but I've got the sunk cost mentality and would really like to win the war against this thing.

I don't have an oscilloscope, so lacking a better idea my next step would be to simply spend the $25 or whatever and replace the flyback transformer, which has been the likely suspect throughout my ordeal. Your comments regarding its potentially short life are a good argument against this approach.

sheldons
01-10-2013, 11:28 AM
it may only fail if you miss something to do with either ht regulation of your power supply-if the ht starts to creep up too high voltage wise over time due to feedback problems -the components used to set and regulate the supply voltage-flyback tuning faults-incorrect line drive,which will damage the line op transistor too...having said this if you have loaded your ht supply with a lamp and checked there is no increase over time with your meter a new lopt should cure your fault as long as there are no other problems.....

wayneh
01-10-2013, 04:17 PM
The schematic was posted in #26. Could I trouble you to translate your advice into specific tasks related to that schematic? I have zero TV experience prior to this project, so the jargon is a challenge for me.

R!f@@
01-10-2013, 06:32 PM
Since the TV is trying to run but goes to stby, you need to look for certain protection circuit

take a look at the video chip IV001. it handles all the deflection signals.
First u need to measure the voltage at pin #36. This pin monitors the EHT, which in short is the X ray protection.

Measure the voltage as stated when the TV tries to run. You need to probe the pin and switch the set ON. The voltage will jump quite fast.

If the measurement exceeds than the stated value, you have a faulty flyback. Remember even 2.5VDC is too much I would say.
Cause from my experience, If I measure around 0.9VDC more is than the nominal value for most Sony CRT, the set goes to stby.

Another problem I find in sony that kicks the x ray is a faulty Vertical Amp IC.

But first you need to tell me the EHT value

PS. Ur 12V supply feed to OK. No need to supply it separately.