Sony KDL46SL140 - Works when hot, doesn't work when cold

[marls]

TV: Sony Bravia KDL46SL140

If the TV is over 90 degrees warm, it works just fine, no problems.

If the TV has an ambient temperature in the 70's or 80's it shuts off during some kind of power on self test. I see the Bravia logo appear on the TV but before I get any control of the TV (within 6 seconds) the relay switches the TV off. It will stay off until I unplug it and plug it back in.

I've taken the back off and looked for swollen caps. I didn't see any obvious ones. I also used my magnifying glass to look for bad solder joints. Again I couldn't spot any.
Since the TV has 3 main electrical boards I wanted to narrow down which board it was. I proceeded to heat up only 1 board at a time to see if I could get the TV working with just 1 board being hot. I tried this for 2 of the boards but even with the boards being hot the TV didn't stay on.

I'm not sure what to really try next. Has anyone gone through something like this before that can offer some further advice?
Thanks!

[tom66]

Re: Sony KDL46SL140 - Works when hot, doesn't work when cold

Have you tried reseating all connectors to see if it could be a loose one?

Try removing the power supply board and checking for cold/cracked solder joints on the bottom of the PSU board. A bad solder joint looks like this:

http://home.comcast.net/~tatng/Auto/...cked-joint.JPG

[marls]

Re: Sony KDL46SL140 - Works when hot, doesn't work when cold

There are 3 main circuit boards in this TV. I'm not an expert, but one is where the power cable is terminated to which I believe is the PSU, one is where all the AV components plug in to, and another is probably a LCD controller bank.

Today I took the TV outside to warm it up. It worked fine. I took out the PSU and AV board and put them in the freezer for 10 minutes. I brought them out and put them in the TV and it worked fine. This proves to me that neither the PSU or the AV board are the problem here.

What else can I look for? Should I do the same with the LCD controller? Should I take out the board that has the power/volume button control? Should I take out the board that has the IR receiver/Status LEDs? Perhaps this is a connector that works when hot. Perhaps the florescent light doesn't work when cold?

[marls]

Re: Sony KDL46SL140 - Works when hot, doesn't work when cold

Attaching picture of back of set. The two boards that seem to be ok when hot or cold is the orange one in the center and the blue one on the bottom right.

[tom66]

Re: Sony KDL46SL140 - Works when hot, doesn't work when cold

Can you remove the orange board (PSU) and try resoldering any joints that look dodgy... like this: http://homepage.ntlworld.com/michael...Solder%201.jpg

If that's OK, then the problem is possibly on the main board (blue one.)

[marls]

Re: Sony KDL46SL140 - Works when hot, doesn't work when cold

Tom66, sorry for being a dork but, I feel like I've proved that the PSU and main board don't have a problem because they work both hot or cold. Looking for dodgy joints on those doesn't make sense to me. Can you explain?

[tom66]

Re: Sony KDL46SL140 - Works when hot, doesn't work when cold

Completely my mistake, I misread your post. So, are you saying when you heat up that board the main board connects to, at the top of the LCD panel, the TV works? That is the T-con board.

[marls]

Re: Sony KDL46SL140 - Works when hot, doesn't work when cold

I believe I have found the problem! The board on the far left which I think is the florescent bulb driver board is definitely the problem. When the entire TV is cool but that board is hot, the TV works.

Upon examining this board I see some melted plastic pieces. I believe this is where the problem is but I don't know how to fix it yet. The plastic doesn't come off very easily to see what is under it. Attached are photos. Suggestions would be great at this point on how to fix the melted area!

[tom66]

Re: Sony KDL46SL140 - Works when hot, doesn't work when cold

Yes, that is the ballast board. This PSU is similar to Samsung and LG, but different from most other TVs, in that it generates one high voltage (approx 3000V) which is distributed to all the bulbs individually. Normally one voltage is generated for each. The black things (transformers) balance the current between each bulb and detect faulty bulbs. I suggest all you have is an intermittent contact, the arcing 3000V has burnt the connector. Use a scourer to clean off the surface and make sure the contact is properly cleaned. Reseating it too, as well as tightening the screws on the ballast board, could help.

[budm]

Re: Sony KDL46SL140 - Works when hot, doesn't work when cold

SONY calls this Balancer board, it works as TOM said. I can see at least 3~4 more in pix #3 that the black plastic pieces are deforming. You should remove the board and clean the copper pads on the board real well with an eraser and then clean them with Alcohol. Clean off any carbon tracks that you can see also.

[ben7]

Re: Sony KDL46SL140 - Works when hot, doesn't work when cold

WOW that is a big fire hazard!

[marls]

Re: Sony KDL46SL140 - Works when hot, doesn't work when cold

TV works great now. I cleaned the contacts just as suggested and now there is no buzzing or arcing. Thanks guys!

[tom66]

Re: Sony KDL46SL140 - Works when hot, doesn't work when cold

Glad to hear you fixed it! A very strange one indeed. Bud have you seen this before?