Help repairing a Sony Trinitron XBR KV-27XBR51 CRT TV

Hello everyone,

I am trying to find someone with CRT Tube TV repair knowledge to give me advice. I'll just preface this by saying, please, do not tell me to throw it and buy an LCD TV lol, I have a very nice HDTV already. I enjoy retro-gaming on vintage console and CRT TV is the best for that kind of old system and that is why I have this old CRT TV around. It is actually a really nice set and was working super until I tried to power it on today. When I press the power button, I can hear the typical tube firing up and hear the classic CRT static coming, but screen remain black and everything stay silent. If I press power again, it does the same thing like it was not on prior. I had that tv for maybe two year and used it from time to time without issue but I haven't turned it on for a few month due to a lack of time to play game. I would really like to have it repaired as it is a very good TV set for retro-gaming and they are getting harder to come by. I have electronic experience but lack the theory to diagnose this issue. I also have a healthy respect/fear for tube TV as I know how dangerous they can be if you are not careful poking around. I am guessing something has issue on the power board and opened it up to inspect what I could but I could not find any component looking burned or capacitor leaking/bulging. Anyone with skill from the older TV days would be willing to help me out? It would be really appreciated! Here's the service manual if it can help out pin-point what could be wrong: Sony Trinitron XBR KV-27XBR51 Service Manual

Thanks!

A common fault would be failure of the frame output stage, which causes the picture and sound to mute. However, first thing you need to confirm is if the line output stage is running, or shutdown - there are a number of 'trips' which will shut it down under error conditions.

Rather unusually, I've never seen one, and I was chief engineer at a Sony Service Dealer (so this was probably never an EU model), it uses an IC PM501 as part of the protection circuit. Presumably pin 8 of PM501 going high shuts the line down?, so check the voltage on pin 8

Thank you for your advices but think I found the cause. I took another look at the power board and something caught my attention. One of the screw holding the board in place look a bit crusty and greenish/oxydized compared to the other screws. I pulled out the board and it seem one of the capacitor leaked and made a mess on the underside of the power board. My plan is to clean up the cap leakage residue and brush up the blackened trace with a fiberglass pen, reseal and then replace the cap (and maybe other around while at it) and pray that it did not fry any others component around.

SkinnyV said:

Thank you for your advices but think I found the cause. I took another look at the power board and something caught my attention. One of the screw holding the board in place look a bit crusty and greenish/oxydized compared to the other screws. I pulled out the board and it seem one of the capacitor leaked and made a mess on the underside of the power board. My plan is to clean up the cap leakage residue and brush up the blackened trace with a fiberglass pen, reseal and then replace the cap (and maybe other around while at it) and pray that it did not fry any others component around.

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Excellent. Good luck !!!

Strange? - capacitor failures are pretty well unknown on European Sony TV's, as they fit higher quality ones than the lesser manufacturers.

Clean it up, replace the cap, and see what happens - what was the number of the failed capacitor?.

Seem to be a 16v 1000uf one.

SkinnyV said:

Seem to be a 16v 1000uf one.

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I meant C??? - so I could look what it does in the circuit.

Oh sorry, I did not read your question question properly. The leaking capacitor appear to be C664.

SkinnyV said:

Oh sorry, I did not read your question question properly. The leaking capacitor appear to be C664.

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You should be OK then, C664 is on the 11V rail, which isn't used for feedback, so hopefully shouldn't have damaged anything else - other then the fluid leak of course.

That’s reassuring, thanks for checking it out for me. I’m a bit more hopeful that I’ll get it back in working order. I’m still cleaning up the leak’s damage but its all big sturdy traces, so it could have been worse. I’ll reflow a few oxydized solder joints and pins, try to replace the cap that are easily accessible and will try it out after!

I finally cleaned most of the damage and replaced the C664 capacitor, but alas, no luck. Pretty bummed out as the tube sounded like it was firing up longer but I'm still not getting any pictures. I can hear the tube slightly crackling similar to wood burning in a bonfire but nothing else. If I press power again, you can hear the tube trying to fire again like before and nothing more. Its a bit disappointing, I really thought this would do the trick

I refer you to post #2.

I am trying to locate that ic, can’t find it going through the service manual for now. I’ll report once I can locate it and test it, thanks.

SkinnyV said:

I am trying to locate that ic, can’t find it going through the service manual for now. I’ll report once I can locate it and test it, thanks.

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It's near the LOPT transformer on the schematic.

I was able to find it on the schematic and it seem to be supposedly located on the A board, but I do not see any component on there named PM501. I saw a series of 10 holes bit but I am not sure I see any component related to this. Am I missing or misunderstanding something? Thanks!

Update: I finally found it, but its so deep within the TV I am not sure how I could safely test that component...

I'm not sure how to proceed, I wanted to try and check the different power lanes on the power board (board F) while waiting to figure out how to safely test PM501, but I am not sure how to proceed since the tv only seem to be trying to power up for a few second and then nothing. So I am unsure how to test the voltages properly. I tried poking around the 18v and 11v lane, for example, if I put my probe on the 18v and the Ground on that connector and turn on the TV, I get only about 2.8v on startup and then it quickly drop down to 1v by increment of 0.1v and then slowly continue going down after until it get to around 0.4v... Any idea what I could test around the power board since it is the most accessible for testing and considering the capacitor damaged occurred there?

Thanks!

I managed to fix it! I went back to the basic and started checking all the traces and solder joints I had cleaned and was surprised to find out that a fairly big trace that looked ok had a micro break in the middle. Soldered a jumper wire and all is back to normal! Thanks everyone for your help!

SkinnyV said:

I managed to fix it! I went back to the basic and started checking all the traces and solder joints I had cleaned and was surprised to find out that a fairly big trace that looked ok had a micro break in the middle. Soldered a jumper wire and all is back to normal! Thanks everyone for your help!

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Brilliant and well done !!