Sound but no picture...

[ozhawk]

Hi, I have an LCD TV, Sanyo DP19640, that has just started to loose the screen image after the warm up (2 mins max). (also if I unplug overnight the picture lasts from 12 to 30 mins. I am a dinosaur at this as I used to be able to troubleshoot issues, but things have changed so much. I saw what I thought was a discharge from one or two disc caps. that I am now finding out may be glue? This is a cheap tv and would be easily trashed and replaced, but I would rather learn/re-learn how to conserve these items and if they are being thrown away, maybe I can fix this one and learn from it and start to re-distribute the crap going into landfils...Just tired of being a dinosaur and a member of a disposable society.....

Here is the two caps that have this brown "glue?" on them-
R4369 R801R7222J RC 2.2K OHM 1/10W ! C518 C03VR0S14K CC 0.01 UF 250V DC R
Can't even read the second cap.
Here is the service manual- (C518)
http://www.toms-service-manuals.com...yo_DP19640_P19640-04_N8ZFE_[SM].pdf&mfg=Sanyo

Can You Help Me Make A Dent...Please?

P.S. Is there an area here where I can learn what you know. Not completely void of knowledge. Electrical wiring/residential/industrial, Kits (Radio Shack), Computer business programming (before laptops), computer builds (before compression of files), now a telecommuter teaching myself programming, electronics, and fishing..(got to have some outlet).
I hope that I don't sound too much like a dribbling fool...

Any Help Would be Greatly Appreciated
ozhawk

 

[tryppyr]

Have you looked closely at the screen after the image is lost to determine whether it is just the backlight going out (as opposed to the pixels no longer being set by the controller)?

 

[ozhawk]

New info. on this

Thanks for the response, I really appreciate it. I remembered that if it was a cap. issue if I reduced the power needed, it may give me an image longer. I turned down the brightness and the backlight settings and got a picture for 30-45 mins. Then I unplugged the tv for a few hours and had a picture at the same settings for over 3 hrs.

But I am still unsure if I should just replace the inverter board.

Thanks
ozhawk

 

[(*steve*)]

Does the screen have any colour cast -- especially does it look pinkish at any time?

I had a CCFL failure on a laptop which exhibited a significant colour cast before/while failing.

In my case the inverter was fine, I had to replace the CCFL tube.

In your case there may be more CCFL tubes, so if one is slightly dimmer and redder, you may not notice. However the failure mode *might* cause the inverter to shut down.

I can see several causes for the problem:

1) inverter failure/failing
2) CCFL failure/failing
3) Power supply problem
4) logic/controller/firmware issue

Those are probably in a rough order of probability, however:

(1) & (2) can be interrelated (each could cause the other).

(3) depends a lot on where the power comes from. Typically it's a separate mains power supply (the inverter operates from the incoming mains). However -- in laptops for example) they operate from a low voltage DC rail.

(4) encompasses a whole series of possible (and many potentially hard to track down) issues. Whilst a low probability, it's always worth checking the power supply capacitors for the main logic power supply. Excessive ripple on this (caused by failing capacitors) can lead to all sorts of weird behaiviour, although it normally presents itself sooner than after 2 hours. In any case it's often a quick and easy thing to look at/repair and is worth examining as a matter of course.

If the inverter board is cheap and easy to replace, then go for it. I've found this to be the most common cause. But also (maybe first, maybe while you wait for the inverter) take a look at the power supply board to make sure it's (and I mean its capacitors are) happy and healthy.

The next step would be to examine the CCFL tubes and consider replacement. Having done a CCFL replacement once, I'd suggest you only ever do it once...

 

[ozhawk]

Color cast ?

Originally before I screwed with the settings and before loosing the picture the image was perfect. I am thinking that it is a cap issue on the pw side because it works so much longer after leaving it unplugged...(are the caps. discharging slowly to the point where it takes a build up before loosing the picture?)..Not going to spend a lot of money on it, but ordered a new board for 24.00.
Just re-sparked my interest in electronics and what I should have kept up with...I really appreciate you guys helping with this and will update as soon as I receive and replace the board...

Thanks
ozhawk

 

[(*steve*)]

Doesn't sound awfully representative of cap failure, but symptoms can be so wide and varied that it's simply good practice to give them a once-over.

Good luck with the inverter board.