Samsung S42SD-YD04 No picture, sound OK

[Karnak]

Took the set apart and the four large capacitors looked swollen on the power board. Replaced all four, thought this would solve the problem, still no picture, Started spot checking surrounding boards all seem to have some power. One board has has a small green led. When set is turned on it is blinking. Have pictures of the power board.

[tom66]

Re: Samsung S42SD-YD04 No picture, sound OK

Can we see a picture of the whole chassis of the TV?

[Karnak]

Re: Samsung S42SD-YD04 No picture, sound OK

The tv is at my nephews will get a picture soon and post it.

[Karnak]

Re: Samsung S42SD-YD04 No picture, sound OK

Was able to get a service manual downloaded. Got over to nephews and got some pictures. First when plunging in the set you get a solid red led light. Press on button, relay engages on power board, red led flashes 5 times and goes out. I check voltages coming off power board all seem good. AS per reading in the manual I check the switch on the logic board. Position 1 on, 2 on, 3 off, & 4on.

AS per the manual I set the switch Position 1 on, 2 off, 3 on, & 4 off.

Quote from manual:

Switch the power on and see if the screen is lit. If the screen can give a normal and
completely white field signal, then the problem lies in our main board or video frequency
processing board, which will be dealt with separately.
d. If the screen is not lit, then first replace the power supply board to see if the problem is
solved.
e. If the problem remains after the power supply board is replaced, then the problem lies in the
screen. Replace the entire screen for treatment.

Screen completely black.

Stumped at this point

[tom66]

Re: Samsung S42SD-YD04 No picture, sound OK

Wow, that's quite an old module. Can you read off the voltages on the sticker where it says "Va 79V" etc just above the PDP Module sticker?

Do you have a digital multimeter (DMM)?

[Karnak]

Re: Samsung S42SD-YD04 No picture, sound OK

Yes I have a DMM. Which board are you referring to and at what point?

[tom66]

Re: Samsung S42SD-YD04 No picture, sound OK

At the top of this picture:
https://www.badcaps.net/forum/attach...2&d=1361665489

you can see a Va: 79V, but I can't see the other voltages. What are they?

[Karnak]

Re: Samsung S42SD-YD04 No picture, sound OK

I will check the board closer. All I was reading were the lower voltages 12, 3.3, 5. I don't see an references to the higher voltages in the schematic block diagram in the service manual.

[tom66]

Re: Samsung S42SD-YD04 No picture, sound OK

Not on the board. On the plasma panel itself.

[Karnak]

Re: Samsung S42SD-YD04 No picture, sound OK

OK will check, may take a day or two.

[Karnak]

Re: Samsung S42SD-YD04 No picture, sound OK

Ok Checked the label: listed the following: VA 79 , VSC 78 , VS 87 , VE 107 , Vset 93. Following values were measured: VA 75 dc , VSC 75 dc - 160 ac , VS 21dc , VE 0 ac or dc , Vset 0 ac or dc. At this point I assume it is the power board. These were test points identified on the power board.

[tom66]

Re: Samsung S42SD-YD04 No picture, sound OK

Vs 87V or 187V?

[Karnak]

Re: Samsung S42SD-YD04 No picture, sound OK

Vs 87 on sticker

[tom66]

Re: Samsung S42SD-YD04 No picture, sound OK

That is extremely low for a plasma panel. I am wondering if this is TERES design like Hitachi used (Y-main/X-main form voltage doubler.) It's a pretty old panel, looks like one of Samsung's earliest modules.

Regardless, since the voltages are low, you should first try unplugging the Y-main and X-main, and seeing then if the voltages rise.

[Karnak]

Re: Samsung S42SD-YD04 No picture, sound OK

I will give that a try. Also a question, should you see ac voltages anywhere, coming off the power board??

[tom66]

Re: Samsung S42SD-YD04 No picture, sound OK

They should all be DC. However, many cheaper multimeters can erroneously interpret some DC levels as AC.

[Karnak]

Re: Samsung S42SD-YD04 No picture, sound OK

Thanks for the response, will get back with info on boards disconnected.

[Karnak]

Re: Samsung S42SD-YD04 No picture, sound OK

Disconnected the Y driver board and the X driver board. All voltages where were they should be. Connected the Y driver board the Ve voltage 0 Vs voltage 19.8 all other voltages ok. Disconnected Y driver board, connected X driver board, Ve voltage moving back forth 31-107 volts, Vs voltage moving 17-36, all others normal. Both boards connected-- Ve 0, Vs 22, all others normal. Seems strange that both X and Y boards bad together.

[tom66]

Re: Samsung S42SD-YD04 No picture, sound OK

It could be a power supply that's struggling under load.

[Karnak]

Re: Samsung S42SD-YD04 No picture, sound OK

Thanks very much for the input, think it is time to retire this set due to the age.