LG 42PC1RR-ZL y sus problem

[luiznunes]

Hi,
I have a LG 42PC1RR-ZL. It has a problem with the picture. When I turn it on, the image is flickering and the pixels are shifting colors.
I notice that on the Y sus board the Vy has 250V instead of 200V, the Vsc is ok, with 120V and the VS has 189V.
After more or less 5 minutes the Vy drops to 200V and the image becames ok.

During the last weeks the time to stabilize the image had becoming from 1 minute to 5 minutes.

Any idea of what component is causing this?

The Y sus is 6871QYH053B. Attached is the sticker with the voltages.

Thanks

[tom66]

Re: LG 42PC1RR-ZL y sus problem

Could be bad capacitors. Providing a clear picture of the power supply and other boards will be helpful.

[luiznunes]

Re: LG 42PC1RR-ZL y sus problem

here are the photos od the Ysus and the power board. I think that is a cap too. but how to discover it? I don't know what causes or what is the path to follow that causes this slow stabilization of the Vy voltage..

[tom66]

Re: LG 42PC1RR-ZL y sus problem

here are the photos od the Ysus and the power board. I think that is a cap too. but how to discover it? I don't know what causes or what is the path to follow that causes this slow stabilization of the Vy voltage..

Feel each cap. Even if slightly domed (bulged), they need to be replaced. It looks like the three caps near the gap between the two heatsinks on the left are bulged.

[luiznunes]

Re: LG 42PC1RR-ZL y sus problem

in which board are you seeing this?

[Th3_uN1Qu3]

Re: LG 42PC1RR-ZL y sus problem

On the power board, left side.

[luiznunes]

Re: LG 42PC1RR-ZL y sus problem

no.. it seems ok..

[luiznunes]

Re: LG 42PC1RR-ZL y sus problem

I took it to the LG repair center, and the technician told me that he replaced the Y sus board and the TV was ok. that's why I am searching on the Y sus..

[tom66]

Re: LG 42PC1RR-ZL y sus problem

The problem is thermal; as the set warms up the voltage normalises.

Some component has become thermally sensitive, either a capacitor, an adjustment or another component on the power supply.

You can try adjusting the Vy control and seeing if that changes the results, but it's likely to be only a temporary fix.

[luiznunes]

Re: LG 42PC1RR-ZL y sus problem

so, there is no fix for this?

by adjusting the Vy control, I will lower the Vy voltage, right? so when it stabilizes, it will bem lower the the 200V necessary, or am I wrong?

[PlainBill]

Re: LG 42PC1RR-ZL y sus problem

so, there is no fix for this?

by adjusting the Vy control, I will lower the Vy voltage, right? so when it stabilizes, it will bem lower the the 200V necessary, or am I wrong?

You are right, and I would take a different approach.

One problem with these is it's hard to find a schematic of the power supply for a plasma TV. I've seen a few, but they are rare.

I'd suggest this approach. With the TV set cold, disconnect the sustains from the power supply. Turn it on and measure the Vy voltage. If it reads 250V, the problem is the power supply, and skip the next paragraph.

If it reads 200V, turn the TV off, reconnect the Z-sustain, turn it on and measure Vy. Turn TV off, disconnect the Z-sustain, reconnect the y-sustain, turn TV on, and again measure Vy. If the problem occurs only when the Y-sustain is connected you have a choice - you can try to locate the problem, or you can buy a replacement Y-sustain. You can use some of the suggestions below for localizing the problem.

The first suggestion would be to try preheating areas of the suspect board with a hair dryer to see if you can eliminate the problem. Pay attention to diodes. Trace the Vy voltage back to the regulator in the power supply.

PlainBill

[luiznunes]

Re: LG 42PC1RR-ZL y sus problem

But the Vy is not generated the Ysus?
I think the power supply only deliveries the Vs. Or am I wrong?

[PlainBill]

Re: LG 42PC1RR-ZL y sus problem

But the Vy is not generated the Ysus?
I think the power supply only deliveries the Vs. Or am I wrong?

No, you are correct, I was wrong. It is generated on the Y-sustain by PS101. That makes it easy - do you want to figure out what is wrong with PS101 or just replace the entire Y-sustain?

PlainBill

[luiznunes]

Re: LG 42PC1RR-ZL y sus problem

Yes, I want to know what is wrong with PS101. It is more fun to repair.
Thank you.

[PlainBill]

Re: LG 42PC1RR-ZL y sus problem

Yes, I want to know what is wrong with PS101. It is more fun to repair.
Thank you.

That should be easy to do. I have a dead Z-sustain which contains a similar supply and just took a close look at it. It is a 4 terminal board which contains a complete DC-DC converter. Troubleshooting is non-trivial, but should not be very difficult. I would look for problems in the feedback loop, either a thermally sensitive component of a bad solder joint.

PlainBill

[luiznunes]

Re: LG 42PC1RR-ZL y sus problem

the PS101 is welded to the board or it comes out from the board from the connector?

[PlainBill]

Re: LG 42PC1RR-ZL y sus problem

the PS101 is welded to the board or it comes out from the board from the connector?

It is soldered in place.

PlainBill

[luiznunes]

Re: LG 42PC1RR-ZL y sus problem

do you know any schematics of the PS101?

I found this one :

http://images3.hiboox.com/images/390...fa988718f8.bmp

[tom66]

Re: LG 42PC1RR-ZL y sus problem

I would check C51, C52 and C54 on that board; they look to be the most stressed components, followed by the solder joints of VR6, R58, R62 and R64. C48 could also cause trouble, but that would be less likely.

[PlainBill]

Re: LG 42PC1RR-ZL y sus problem

do you know any schematics of the PS101?

I found this one :

http://images3.hiboox.com/images/390...fa988718f8.bmp

That is similar to the one you have, but there may be significant differences, particularly in the value of resistors. I would pay particular attention to IC11 - the TL431 and the variable resistor.

PlainBill