Sony XBR-43x800e TV had sudden loss of picture

[beenthere7]

Sony XBR-43x800e TV had sudden loss of picture. Screen is dark except for backlight. Sound is present. Main and T-con boards have been replaced (T-con twice from sets with reportedly cracked screens) with no improvement. When one side of the cable between T-con board and display panel is disconnected (call it the “bad” side), the corresponding half of the panel is white and the other half black. When the other cable from the T-con board to the panel is disconnected (with the “bad” side cable reconnected), the whole screen remains black except for the backlight. I've tried blocking several groups of pins on the bad side ribbon connector without improvement (although I have not tried all combinations).

Capacitors were tested on the display panel boards with both cables to the T-con board disconnected. Seven capacitors displayed evidence of shorts on the “bad” side, none on the other (“good”) side. (With both cables reconnected between the panel and T-con board, two capacitors on the “good” side appeared to be shorted, but that resolved when the cable on the bad side was disconnected.)

So it appears there are one or more capacitors on one side of the display panel board that are shorted. I realize that some capacitors on the panel board may be in parallel, but is it possible that 7 could be in parallel across the length of the board? Is it possible to determine which capacitor(s) is/are shorted without de-soldering one at a time? (All look OK.) Can these types of capacitors be replaced, how important is it to replace a removed shorted capacitor, and how can one get a replacement? Has anyone on the forum had experience replacing them?

Thanks!

[alfatv]

Re: Sony XBR-43x800e TV had sudden loss of picture

Yes, most likely they are in parallel, this is normal.
If you can get 6-digit meter that goes down go milliohms, you can find short location by minimum resistance.
It may work OK without capacitor in terms of image quality.
But, this may cause EMI/radio interference and FCC may be after you LOL.

[beenthere7]

Re: Sony XBR-43x800e TV had sudden loss of picture

Thanks, alfatv.
After reading your post, I went back and re-measured resistance across the capacitors with my multimeter, which has a resolution of only tenths of ohms. It's difficult to make sure one has good contact with these tiny capacitors, so there may be some residual resistance with the probe contacts. However, I did notice that there was a progression of resistance across the “shorted” capacitors from one end of the board (1.2 ohms) to the other end (0.8 ohms on 2 capacitors). So maybe it's one of the 0.8 ohm capacitors that I should start with. But after carefully re-measuring the resistance, I'm also wondering why a “shorted” capacitor doesn't have 0 ohms (at least to a tenth of an ohm resolution), and whether there may be something else shorted.

[Davi.p]

Re: Sony XBR-43x800e TV had sudden loss of picture

Don't ask yourself why, shorted caps in this area is very common so start to dissassemble one by one from the lower resistance to gnd, keeo in mind smd components usually must be scratched to test them cause them has a transparend film of insulating rosin, so scratch them all and retest ohms
I have bought a soft metal brush to do this iob..

[alfatv]

Re: Sony XBR-43x800e TV had sudden loss of picture

Thanks, alfatv.
After reading your post, I went back and re-measured resistance across the capacitors with my multimeter, which has a resolution of only tenths of ohms.

This is not milliohm meter, you got what's expected with your meter

[RDC55]

Re: Sony XBR-43x800e TV had sudden loss of picture

I just did one on a Samsung 60 inch and tried the low resistance method, which I have had good success with before. Unfortunately this time no luck.

I then took a variable power supply and connected it across the shorted caps and adjusted the voltage until the current meter read 250 mA. If I then had a FLIR camera it would have easily found the shorted cap, but I was able to use my pinky finger (most sensitive) and feel the warmth in the one that was shorted after about 1 min.

The drawback is that too much current might risk etch damage, so proceed wtih caution. Or maybe others will just say this is a bad idea.

These groups of caps on the Samsung happened to be 1 uF, but they seemed to vary a lot as I had some other scrap panel boards and could not find one that matched and had to order replacements. I identified the value by removing the adjacent cap on that line and measuring it with a cap meter. As for voltage it was a 17V line so I selected a 50V cap.

Oh, and yes the TV operated normally with the shorted cap removed and the spot blank, but being on the paranoid side I imagined how the missing cap would allow some EMI spike to find its way into the source driver chip that this cap is protecting and render the TV useless.

And since there is always hind sight I didn't even try feeling the caps with the TCON drive signal providing current to that line. I might have been able to feel the warmth if the TCON supply was in a steady state current limit condition, so I should have done that.

[beenthere7]

Re: Sony XBR-43x800e TV had sudden loss of picture

I went ahead and desoldered one of the capacitors that read 0.8 ohms. (It measured around 2x1x1 mm, but many on the board were even smaller.) It turned out that was the bad one, as after it was desoldered, there was no longer evidence of “shorts” on the other capacitors. The picture is back on and looks fine! While I have had some experience repairing electronic devices, this was definitely challenging. I appreciate the information on the posts.

[Davi.p]

Re: Sony XBR-43x800e TV had sudden loss of picture

RDC55 the current limiting method is ok, It is possible to set output of 15v (good for all lcd) and start increasing current from zero, with short the voltage self adapt from low, very slowly until you feel warm on a cap, no need for thermo cam, for the cap replacement i always take one random from a cracked panel board, with at least same period, same size, i don't think them are for EMI, i think them are leveling tank put near the loads for esr reducing reasons, so it is good to replace them , in fact on the tcons there are few capacities usually because there are on panel's boards.

[alfatv]

Re: Sony XBR-43x800e TV had sudden loss of picture

i don't think them are for EMI, .

Decoupling caps are there for multiple reasons, but EMC is what will fails first even if device is functioning "properly".
RF interference is not necessary affecting device itself, it could be anything else like cellphone, wifi, gps.
So, for compatibility FCC, CISPR and other bodies defined RF emission limits. These are tested by manufacturers to ensure compliance and many times these are tough to meet, so they take extra measures like redesigns or band-aid fixes.
Go ahead, remove capacitors, conductive tapes and so on. If anyone here says it's OK, take it to EMC lab and see if it will pass the test.