Who has dabbled in TV repair? Have an issue

[meenmeen1103]

I have a 5yr old-ish Sony Bravia that has no image (no backlight, nothing) and assuming no sound. Power led on solid green as normal. No visually damaged components to my eye, no water damage. I've checked the rails, all voltages present. Relay for 12v also clicks when powered on. Power_on does alternate from ~0-3V when TV powered on/off, but backlight_on only alternates from ~.1-1.2v. I'm guessing that's not enough variance, and that the mainboard is faulty? 

[meenmeen1103]

A side note: the red optical out light comes on when TV is first powered on, but then fades out in one second. Don't know if that's normal, but all devices I've paid attention to normally have that stay on while unit remains powered on.

[Bananasplit_00]

would say main control board is bad here, i dont know super much about TVs but thats my guess here

[Mohenjo]

could be a leaking fuse, thats a very common issue with older tvs. 

[meenmeen1103]

Just now, Bananasplit_00 said:

would say main control board is bad here, i dont know super much about TVs but thats my guess here

I'm guessing the same, just looking for other opinions since I'm not well versed at all in TV repair.

[meenmeen1103]

15 minutes ago, Mohenjo said:

could be a leaking fuse, thats a very common issue with older tvs. 

You mean the AC line in fuse or some resettable fuse elsewhere

[Hackentosher]

@iamdarkyoshihas done some TV repair. 

[iamdarkyoshi]

Unplug the backlight. Turn on the TV. Use a flashlight to look at the screen, if it has an image, either the PSU is aging, or there is something wrong with the backlight.

 

Sounds like the board's CPU is responding, so thats good.

[meenmeen1103]

17 minutes ago, iamdarkyoshi said:

Unplug the backlight. Turn on the TV. Use a flashlight to look at the screen, if it has an image, either the PSU is aging, or there is something wrong with the backlight.

 

Sounds like the board's CPU is responding, so thats good.

Had used a flashlight to look for an image, couldn't see anything but glare from flashlight and darkness. Didn't try with backlight cable unplugged, although the backlight was most definitely off.

 

Here's the update: I took the backlight_on wire out of the connector from power board to main board, and plugged everything in. Still measured only 1V out of the main board without load. I jumpered from the 3.3V pin on power board (which is the same amount of voltage used to trigger power_on) to the backlight_on on power board and got a backlight but still no image. The main board definitely seems to at minimum be failing to send that signal correctly. Probably also the reason no image is displayed, and also would explain the optical out light behavior if that indeed isn't normal behavior

[corrado33]

Check for leaky/exploded caps in the power supply. That's generally the first thing I do to try to repair a piece of consumer electronics. (And sometimes the last.) You aren't going to get away from this without soldering something, so if you're not comfortable with that then... I'd stop now.

 

Many of the times that TVs and stuff are broken it's simply because of a bad power supply. I mean, just watch any of the electronic focused channels on youtube. (EEVBlog, The Signal Path, etc.) All of them (Especially the signal path) have at least one repair video where it's fixed by simply fixing the power supply. In fact, the first rule of electronics troubleshooting is "Thou Shalt Check Voltages." If your voltages are not what they should be, then you either have a short, or the power supply has failed. Make sure the power supply outputs the correct voltages before you try to "fix" anything else. 

 

And freaking be careful. Messing with mains voltage power supplies is a good way to get a shock. Even after they're unplugged the caps can (and will) still hurt you.

[Huntsman]

Try measuring ONLY the PSU. Unplug it from everything else and test that. Then plug it back in and see if there's a difference. Modern electronics are getting more and more difficult to repair because they integrate almost everything together now.

[Scheer]

What model?

 

If you can get one cheap enough on eBay (~$20) I'd throw in a T-Con board.... May or may not fix the issue, but if you have voltage and image at all it is where I would start.

 

 

[meenmeen1103]

Quick update:

After a seller shipping the wrong board and waiting on post office for the correct board, finally got the correct mainboard in today. Seems like my guesswork was right, a simple mainboard swap and the TV is back in working order. Was honestly not expecting it to be so straightforward but I saved myself from doing any more solder work or light component level repair in general (I only do this as a hobby for the learning experience) and all with $100 that wouldn't buy 1/3 of what the current TV is capable of.