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-   -   Sony Bravia no picture but backlight on (https://www.badcaps.net/forum/showthread.php?t=8606)

capxrf 01-02-2010 09:54 PM

Sony Bravia no picture but backlight on
 
Hello, Iím new to posting, but not at all new to reading here. Thank you all for all your past help you didnít know you gave!

I just bought a really cheap Sony Bravia TV with no picture for myself to fix. I have a good deal of electronic repair experience, and have been doing a lot lately, so I figured this would be relatively simple, but no go, so hereís the deal.

Itís a 32Ē (31.5Ē diagonally) Sony model KDL32s5100. The tv turns on fine. Green power light comes on solid and stays on. Backlights are bright. Unit is in great condition and hardly used it appears. Not tampered with.

No picture though. No menu, nothing but backlit screen (screen is perfect). I can change the brightness with a combination of button pushes, so I can assume the menu is working, just I cant see the graphics.

No bulged electrolytic caps. Touched up any iffy solder on power supply (no change). No cracks. All wire connections there. All insulators intact.

Two strange things:
1) I read 56 volts from 3 heat sinks on the power supply to ground (hurt to find out) (is this normal? Iíve never seen it)

2) one pin off the power supply says 30v 2mA on the board, but only tests 17v. (I donít know why, and canít figure how everything can work but the screen if the power supply is bad)

Any suggestions? Where should I be looking? Iím thinking main board, or power supply, but donít know what Iím looking for on the main, and the power is on.

Any help is great, I really want to fix this one.

Thank you !

capxrf 01-03-2010 02:45 PM

Re: Sony Bravia no picture but backlight on
 
Alright, I was more thourough today and tested the power supply again. All output wires are correct, (the two pins labeled pwr_panel tested at about 3.5v, I assume this is correct as everything else is and the two pins are identical) and the supply grounds are good. Still have 50 some volts over those three heatsinks, but i ust don't touch them, and they are obviously designed that way

So now I'm stuck again. Anyone have any experience with this?

stj 01-03-2010 04:18 PM

Re: Sony Bravia no picture but backlight on
 
download the schem's if you can find them - some are around.

look for voltage regulators on the scaler/processing panel & check there outputs.

capxrf 01-03-2010 04:53 PM

Re: Sony Bravia no picture but backlight on
 
Thats where you lose me a little. What am i looking for in the way of voltage regulators? everything is tiny on the main board. Am i looking for a chip? I've been searching for schematics. I'm having a time locating any

capxrf 01-03-2010 07:48 PM

Re: Sony Bravia no picture but backlight on
 
Alright, I guess I need more help than i even thought. I can't find the service manual/schematics for the tv either. I found one for a model KDL-32L4000 and KDL-37L4000. The boards look the same visually, but the manual isn't for my model

infringer 01-03-2010 08:14 PM

Re: Sony Bravia no picture but backlight on
 
Look for chip id's with a magnifier look those ID's up ... You will find out what there functions are voltage regulators if you google that what does that bring up for you to me a complete newb anything that regulates voltage is a voltage regulator... So I see where you would be lost as well...

But I remember chips that show LMXXX as being voltage regulators this may be what you are looking for as well...

http://www.national.com/cat/index.cgi?i=i//75

This may help you a little bit...

PlainBill 01-03-2010 09:06 PM

Re: Sony Bravia no picture but backlight on
 
I've said this repeatedly to others, now it's your turn. Attach good quality pictures of the boards to your next post.

PlainBill

stj 01-04-2010 04:23 AM

Re: Sony Bravia no picture but backlight on
 
oh yea, there was a sony alert to repair centers about some large bravia's
if you have a long board at the side with loads of invertor transformers on it, and it has a plastic cover over it - take the cover off.
it traps the heat and causes faults!

infringer 01-04-2010 06:45 PM

Re: Sony Bravia no picture but backlight on
 
Wow stj that is good information to know thanks a million man makes perfect since to me. Great tip.

capxrf 01-05-2010 10:02 AM

Re: Sony Bravia no picture but backlight on
 
Well, since the backlight is looking good and bright, would the inverter board even be an issue? All it does is backlighting right?

It's gonna take a while for photos to load up for me, but they're on their way

capxrf 01-05-2010 01:31 PM

Re: Sony Bravia no picture but backlight on
 
6 Attachment(s)
Here are the pictures

The first is of the back of the tv with all boards uncovered

second is the main board

third is a closer view of main board

fourth is the inverter board

fifth is the power supply

and last is the little board at the top of the tv between main board and LCD screen

Wizard 01-05-2010 03:49 PM

Re: Sony Bravia no picture but backlight on
 
Blindly change to a video input with video and audio attached. If you get audio, that means TV is fine and whole LCD panel is probably good, that why I suggest check fuse on T-CON board, fuse is small and usually marked with a one letter and is very close to the LVDS connector. This can fail. That last picture is called T-CON (timing control). If fuse is still good, see if you can get one from sony or ebay or google may find one.

That one is a square cross section fuse with metal square end caps and it does have a number marked on white body. Fuse is just above the LVDS connector to the left. They sometimes fail for no reason. Changing fuse or solder a picofuse over the old fuse is sufficient.

Cheers, Wizard

capxrf 01-05-2010 04:59 PM

Re: Sony Bravia no picture but backlight on
 
Yes, I had already checked the fuse on the T-CON board (thank you for the new name). It tests positive for continuity. You said to "Blindly change to a video input with video and audio attached". The only connection like that I can think of is HDMI or the coaxial, am I correct? I'll have to find someone with an HDMI output device since I can't see anything to set up with my converter box... I'll get on that soon hopefully.

Wizard 01-05-2010 05:53 PM

Re: Sony Bravia no picture but backlight on
 
Use the source that you can plug to the TV. composite, component with audio cables or composite even s-video with audio cables.

Trying to blindly tune to a channel is harder.

Cheers, Wizard

capxrf 01-05-2010 07:04 PM

Re: Sony Bravia no picture but backlight on
 
oh, well then yes, I can indeed get audio from Component #1 with the television. I can't seem to make the audio switch to the other sources though with the "input" button.

Wizard 01-05-2010 09:01 PM

Re: Sony Bravia no picture but backlight on
 
This means mainboard is fine. Either replace the T-CON, but make sure you have voltage on that fuse. Failing that, LCD panel itself.

T-CON on used market is usually 50-120 dollars. Panel is around 800-1,500 in that size.

Cheers, Wizard

capxrf 01-06-2010 12:47 PM

Re: Sony Bravia no picture but backlight on
 
Is there a way to determine which is the issue first? $50 would be worth it, but not if I found later that the screen was gone too (can't afford that for a free tv).

Wizard 01-06-2010 05:19 PM

Re: Sony Bravia no picture but backlight on
 
Cannot do. Only way is get a T-CON and try. If not, you can stilll hold on it and get another one or sell the TV in pieces on ebay.

Cheers, Wizard

capxrf 01-06-2010 07:57 PM

Re: Sony Bravia no picture but backlight on
 
Dang. Well then, I'll do some searching for another for a bit.

I do have a "32 Toshiba Regza with a smashed screen. The T-CON boards on them look different, but just to check... this other tv couldn't help me any could it?

Wizard 01-07-2010 08:32 AM

Re: Sony Bravia no picture but backlight on
 
Not compatible at all. Had to be *exact*. Sony is odd out.

Spend that money, that Sony is way too good to waste. S5100 series is nice.

Toshiba tend to use normal LCDs.

Cheers, Wizard


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