You're concerned about inconsistent voltage?

 

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.

 

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.

 

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.

 

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.

 

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).

 

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.

 

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.

 

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.

 

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

 

...dont give up on the set just yet

Ha! 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.

 

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.....

 

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.

 

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.