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.

 

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.
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 for <$20. No mention of a warranty.

 

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.

 

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?

 

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 (132±2V, I think).

 

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.

 

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.

 

The full schematic and training guide were posted in #26.

 

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.

 

..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 from someone with experience with this set.

 

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

 

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 0.1µF, on the end of the probe?

 

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.

 

... 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.

 

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

 

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.

 

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.

 

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@@

 

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.

 

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 ?