Sony Bravia KDL-46XBR4 shuts off after few minutes. HELP !!!

[wtuser]

Hello,
My 10 yr old tv has developed a problem of shutting itself off after working perfectly fine for few minutes. Both picture and audio shuts off with power LED green and Sony logo lit. If I turn it off for little while, it works fine for little bit before repeating same symptoms. It seems, the backlight does turn off when this happens along with no audio.

Initially I thought, it was a overheat problem but problem persists after cleaning it thoroughly from inside. Weird thing is, if I use it with the back open, it works perfectly for hours but as soon as I put the back cover back on and hang it, it starts acting up. I've also verified that cooling fans are operations.

Now I am thinking it could be some sort of feedback protection circuit that's turning it off. GF1 power board looks good with no apparent capacitor damage/leakage. Obviously, everything else works for few mins when I first turn it on before going dark.

I don't want to start throwing parts at it. I would appreciate your input to get a direction on this.

Thanks -

 

[73's de Edd]

Sir wtuser . . . . .

That set is certainly old enough to be experiencing marginal / declining electrolytics.
Or you could have backlight drop out and resultant shut down.
Initially . . . . considering the power supply . . . . . .
Your hot / cold experience is just the OPPOSITE of as is usual . . . as typically a marginal ESR cap will sometimes start working a bit when its heated up.

Initially concentrating on the mentioned GF 1 power supply board . . . you can see those geeee-i ant two electrolytics used for raw DC power filtering
Using them for initial referencing landmarks, move to the right until you see the 18 pin IC 6100, controller / drive and its surrounding E-caps of interest . . . the C6102--3--4-- and 7 E-caps..
See if you can have the back cover off and supposedly then being able to work for hours.
Confirming its running in that state . . . commandeer Mamma Cass's blow drier and direct short wafts of heated air upon those specific E cap units to see if the unit fails.
If not, then get just a bit more aggresive in the heat level . . . . but NOT to a level of the wrinkling / burning of their plastic shrinks .
If no shutdown, then move across the board to the right, over to the rectified LOW voltage sector, with its relevant caps as being the larger C6165 and C6160 and the two other units higher up on the board.
Give them a like gradual heating up procedure.

Waiting for your confirmation of comprehension as well as if any questions . . . . .

73's de Edd

 

[wtuser]

Hello Mr. Edd. Thank you so much for your response. Out of caps you mentioned only C6104 looks suspect. Although not obvious, upon closer look, it might be starting to fail. See pics below.

I did run it with back cover off and it worked just fine for more than an hour. That's why I think applying heat on caps may help. I just have to be sure that it shuts off because of the heat I'm applying and not because of something else.

Let me know your thoughts if you see anything else.

Appreciate the effort.

 

[wtuser]

Hello Mr. Edd,
Hope you had nice Thanksgiving.

Following up on my issue here. This time when I ran the TV with back off, I noticed that the backlight is in fact shutting off when the TV goes off. Odd thing is, I don't get any blinks (Red) on standby light indicating error. FB1 has heartbeat so I thought TCON might be an issue but since I have no glow, I'm thinking driver board (DF2&3) or the inverter boards. Worst case bad panel. Also checked standby voltage along with 12v/6v references on DF2&3 and all look normal.

I did try to take power off DF2&3 at a time to see if I get panel to glow with some sort of picture on either side but nothing. Couldn't find literature on UB1 as far as any test points or ref voltage.

Again, this is hard because I have no blinks on standby light. Any thoughts on how to isolate the issue between TCON, inverter boards and panel?

 

[wtuser]

Just posting an update on this problem. Ended up replacing AU & FB1 as I wasn't getting 3.3v backlight trigger on GF1 power board. Now I'm getting as far as menu but no video on any of the HDMI sources. Checked the support menu and noticed that I need to change the serial and model#. Only problem is, I'm unable to figure out how to change model/serial# in the service menu. Anybody know how to update this info in the service menu. Sony support site has no update on firmware so I have no way to do that. I would at least like to change serial/model to see if I get video sources working. Any thoughts? TIA