Toshiba Picture Fades To Black But Audio Continues

[hairyturtle]

Toshiba 42HL167 . Picture fades to black after a few seconds. It use to be after a few hours, then after a few minutes but now after seconds. I bought and replaced PS board, then Input board, then Low B board. The only board left is the 'Seine/Input' board. I guess I'll try that one too but am very frustrated and don't think this will work either. Here's a short video I uploaded that shows the problem:

http://www.youtube.com/watch?v=q06jYJ2nbXs&feature=plcp

Any ideas would be welcome. I'm no expert on electronics (internal combustion engines are my game)!

[Hobby 1]

Re: Toshiba Picture Fades To Black But Audio Continues

I can't tell from the video if the backlight is still on. Is it? If it is, then I would suspect the tcon board. Looks like somthing overheats quickly and kills the video.

[tom66]

Re: Toshiba Picture Fades To Black But Audio Continues

It's hard to tell but it looks like the video freezes and then it fades out in bars - this points to T-con as Hobby 1 suggested, or possibly panel...

[hairyturtle]

Re: Toshiba Picture Fades To Black But Audio Continues

Thank you for your inputs. Two followup questions:

Where is this Tcon Board located. I don't see that on the rear side of the tv. Is it behind the panel/screen?

Also, when you inquire about whether the screen remains 'backlighted', what do you mean by this? Are you asking if the picture screen reverts to its black 'off' condition vs. backlighted which would show some sign of a grayish, lighted screen?

[tom66]

Re: Toshiba Picture Fades To Black But Audio Continues

T-con is at the top of the screen (sometimes at the bottom on newer sets) and connects to the LCD panel itself and the main board. It's not the power supply, which connects to the mains power, or the main board, which has video inputs on it.

[Hobby 1]

Re: Toshiba Picture Fades To Black But Audio Continues

Backlighted means the lamps are on and you can see bright lights in the back of the screen through the little holes. If the lamps are on and all you see on the screen is a grayish lighted screen, it is a bad tcon board. Get the part number off your board and start looking on ebay. Get the exact same one. Match the ebay pic with yours. The same model set can have several screens used during production.

[RON_CET]

Re: Toshiba Picture Fades To Black But Audio Continues

Here's some things might help with your troubleshooting, hope this helps

[tibimakai]

Re: Toshiba Picture Fades To Black But Audio Continues

Did you managed to get to the bottom of this issue?
I have the same TV with a very similar issue. I can't see those vertical lines on mine though and the black spreads from the center outwards (as if you would pour a black fluid on the center of the screen and it spreads outwards).
The TV runs for good while until this issue comes up.
I know that I should check the T-con, that is why I'm asking before I take the whole TV apart, I don't even see where the T-con is located.

[Techstar]

Re: Toshiba Picture Fades To Black But Audio Continues

You will probably need to take all of the boards out and do a lot of dismantling to get access to it. Be carefull when unplugging it's connector
it's easy to bust these connectors to the tcon board , when fitting or handling the
new one use anti static wrist band. I have not done one on this particular
tv so i don't know the finer details of how to get to it.

[tom66]

Re: Toshiba Picture Fades To Black But Audio Continues

You can try heating t-con with a hairdryer to see if issue occurs immediately. When something gets hot in this TV, it malfunctions.

[tibimakai]

Re: Toshiba Picture Fades To Black But Audio Continues

I have taken this TV apart and did some measurements.
Most of the voltages are fine, but two of them are much higher compared to there markings.
There is a voltage of 40V marked and I'm measuring over 48V and the second voltage is marked 18V and it's alnost 21V.
One of the double diodes (D870) in the secondary installed on a heatsink with other two double diodes it's getting pretty hot, 66 C. If I have read the schematics correctly, that is the inverer 24V power supply.
The inverter seems OK even after the back screen shows up. Backlight stays on, sound is still on.
Capacitors are Nichicon, none of them seems bad, but I will check them anyway.
Any input would be appreciated.

[tom66]

Re: Toshiba Picture Fades To Black But Audio Continues

I've worked on the 32WLT66 and saw a high 48V on 40V, but my 18V was dead 18.2V. Still, the 18V only powers standby regulators, and it's regulated down to lots of different voltages across the boards.

If it exhibits the same symptom, you can clearly see the backlights are on, so it is not a backlight issue, it is t-con, or power to the t-con, or panel.

[tibimakai]

Re: Toshiba Picture Fades To Black But Audio Continues

These are the voltages that I'm getting:
Inverter connectors are getting exactly 24V
main PS connector:
18V= 20.89V
40V= 48.05V
Aud Vcc= 30.32V
Pow Sig= 3.28V
5V1= 4.9V
secondary small PS connector:
24V inv=24.2V
6V= 6.39V
12V= 11.80V
CV61 connector from main board to T-con:
4.87V
3.09V
3.39V
0V
If I pull this CN61 plug or the LVDS cable from the mainboard the backlight goes off too, that is normal?

[tom66]

Re: Toshiba Picture Fades To Black But Audio Continues

Can be normal on some sets if t-con controls backlights - for dynamic dimming. I'd try freeze spraying t-con to see if you can wake it up again.

[tibimakai]

Re: Toshiba Picture Fades To Black But Audio Continues

I don't have a freeze spray. Can I use a air spray upside down? The problem is that some fluid comes out and I'm afraid to spray that to live boards.
I have sprayed to the panel, but nothing has changed.

[randtek]

Re: Toshiba Picture Fades To Black But Audio Continues

That liquid is electronically inert. You can safely use it on live electronics. I do it often. Even using it until the board frosts up is fine.

[tom66]

Re: Toshiba Picture Fades To Black But Audio Continues

That liquid is electronically inert. You can safely use it on live electronics. I do it often. Even using it until the board frosts up is fine.

I thought that. And indeed, it is -- up to a certain point. I was spraying a power MOSFET in a PFC section with the stuff when BANG... everything tripped. Luckily, the PSU survived with no damage, it just tripped the breaker. So I don't know if I was using cheap stuff or was just unlucky.

[randtek]

Re: Toshiba Picture Fades To Black But Audio Continues

I thought that. And indeed, it is -- up to a certain point. I was spraying a power MOSFET in a PFC section with the stuff when BANG... everything tripped. Luckily, the PSU survived with no damage, it just tripped the breaker. So I don't know if I was using cheap stuff or was just unlucky.

Good to know. Use with some care in high voltage areas. Thanks Tom.

[randtek]

Re: Toshiba Picture Fades To Black But Audio Continues

OT - I once saw a guy spray "Flux-Off" on the HV anode of a CRT set. It resulted in about a 1 1/2 foot (1/2 meter) fireball flash right in front of his face. Didn't hurt him, can't say the same for his underwear!

[tom66]

Re: Toshiba Picture Fades To Black But Audio Continues

Also OT: I built a little breadboard project using the flyback transformer from a plasma ball. I was able to generate up to 30kV arcs from 20V in, quite impressive, though they only tingled. I accidentally spilt some water on the oscillator, so immediately grabbed my compressed air can to clean the board. I'm sure you can understand that propellant around an arc is not, in general, a very good idea. Nice fireball! but amazingly, no damage to the circuit, or to my eyebrows that day.