Sharp LC-42D43U - sound but no video

[ahickman]

I pulled another set today from the dump. Its a Sharp LC-42D43U. Powered it up but no video. Used a VGA input. I've got sound, but no video. Below are some other details:

1. Backlights do come on when powered. Although, the seem to dim after about 10 seconds.

2. Besides the blue hue from the backlights, I don't see any images.

3. OPC and Power LED are on. They are steady and not blinking.

4. TV responds to the input, PWR, Channel and Volume buttons as expected.

Searched the forum and other sites for similar symptoms on this set. Found a number of threads related and tried a "factory reset using the VOL-, INPUT and PWR buttons. No change. Found the SM here:

http://www.toms-service-manuals.com/....pdf&mfg=Sharp

As much as I could, I sorted through the schematics and found the expected voltages on ribbon cables from the power supply to the main board. All were in specifications.

I suspect the LCD controller / t-con card is defective. Can anyone make a suggestion? I don't see any details about the t-con in the SM. Pictures of the t-con are below.

Thanks.

[tom66]

Re: Sharp LC-42D43U - sound but no video

Fuse F1 is OK?

[ahickman]

Re: Sharp LC-42D43U - sound but no video

Certainly is!

[tom66]

Re: Sharp LC-42D43U - sound but no video

Not many test points there - hoping for somewhere to check VGH or VGL voltage, can you see one?

[ahickman]

Re: Sharp LC-42D43U - sound but no video

Nothing that I see so far.

[tom66]

Re: Sharp LC-42D43U - sound but no video

Around that main SHARP chip there are lots of smaller capacitors, brown colour surface mount. You can see the thick tracks going into them. I'd check the voltage across each. You're likely to see 3.3V, 2.7V, 2.5V, 1.8V, 1.5V and 1.2V.

[ahickman]

Re: Sharp LC-42D43U - sound but no video

Tom66, I checked voltages around all SMD caps and found 3.3V, etc. I then looked at the larger SMD caps (orange color) in the bottom left corner which filter the bank of transistors. I found no voltages across any. Then went looking at the two SMD chips directly above them. Only found voltages on one or two pins. Picture of the area is below.

[tom66]

Re: Sharp LC-42D43U - sound but no video

I think that might be a set of voltage references... (positive and negative possibly?) not sure though what voltage to expect at those points.

[ahickman]

Re: Sharp LC-42D43U - sound but no video

D1758's are NPN transistors. They should show a voltage across the emitter/collector, correct? The B1182's are PNP from a quick search.

[tom66]

Re: Sharp LC-42D43U - sound but no video

It depends on how the transistors are driven and their set up, you cannot say definitively.

[ahickman]

Re: Sharp LC-42D43U - sound but no video

I've searched and searched for any schematics or info on this or related boards. Almost thought about buying a replacement board, but am too stubborn to quit. Anyone have any suggestions on what to look at on this board? The two IC's (Sharp LZ9FB27 and TB728A5) are scarce in terms of info.....Help!!!

[budm]

Re: Sharp LC-42D43U - sound but no video

Those 6 transistors, are the Collector (BIG TAB) of the NPN connected to the B+ fuse that feed to T-CON board? And the Collector of the PNP connected to Ground? In each pair the Base of NPN also tied together to the PNP, the Emitter of both transistors are also tied together and seems to be the output connection. It looks like Totem pole output, when the Base is HI, the NPN will turn on, when Base is LO, the PNP will turn on.