First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

[johnboy1313]

I just want to post these pics to ID what's what inside this thing. I've read a bunch of posts. I suspect the Y-Sus or one or both of the buffers, but I'm not really sure about everything I'm looking at.

To start, power supply. Several bad caps. I'll replace them but I'm not expecting it to fix the problem.



Main board


Z-Sus and label



Y-Sus and label



Y-Driver?? and label



I don't know what this board is. I thought I got a pic of this board. It runs along the bottom of the panel.



I don't know what this little guy is peeking out from behind the right side of the main board. (last two pics should have been rotated 90 degrees)



I'm working out of the office tomorrow so I won't be around much to answer question. I probed six fuses in all. Two glass fuses on the Y-Sus, two glass fuses on the Z-Sus, one surface mount fuse on the Z-Sus, and one glass fuse on the power supply. They all test good. That's as far as I got. It's late and I'm going to bed. I'll get back to you tomorrow afternoon sometime.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

So it seems that the "one" long board on the bottom is actually two boards. Are those the upper and lower buffers?

[mattpd]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Your upper and lower buffer are on the far left side of the tv if you are facing the back (skinny vertical board). Looks to be one piece on this tv. You ysus board is the one with big heat sinks connected into the right side of the buffer. Your xsus (or zsus, I forget what lg calls it) looks similar to your ysus and is on the far right of the tv


I fixed almost the same tv with the same problem with a new ysus board. I think the IPM failed, but I didn't bother to check because a replacement board was cheap. Those caps might have something to do with the ysus. Maybe replacing them will provide proper voltage to ysus and bring the tv back the life. If not, time to check voltages

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Those caps go bad because they are Samwha. Since there are so many the TV only starts having problems a few months from now.

The long board along the bottom of the plasma panel is the X drive distribution board.

The board underneath the main board is the control board.

Check the Y-sus fuses.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Just getting ready to head out for the day. I've read that you can test the buffers by disconnecting one or the other to see if half of the screen lights up. It looks like that is not possible on this set. Am I correct?




Tom, I checked the fuses, they all seem to be OK.

[rayrod81]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

It is possible that IPM has failed open circuit and it will not blow the fuse. This IPM failure is by far the most common problem on these sets. It is possible that the caps are causing the no picture condition as they control the low voltages going the main board but if that does not fix it then it Y-sus IPM is probably the culprit. The IPM can be found for $20-$30 if you use the Sanyo STK795-820(or 821) or $40-$50 if you use the LG YPPD-xxxx module. You will need to know which chip is on the board now as the STK795-xxx chip may not be compatible with all versions.

Be aware that unless you have a very high temp soldering iron and take your time (it can take a good 30 minutes or more to remove the chip) then you will be very likely to damage the board. Also, even after the TV is fixed you may notice red, blue, and green sparkles that cannot be fixed without a special jig to update the firmware on the Logic Board.

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

The IPM failures, and the sparklies issue, are two reasons I stay away from these sets.

Note I have never heard of a bad Y-sustain killing an LG buffer board, though I wouldn't rule out the possibility.

[mattpd]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

What is the board number on your ysus? IPMs are expensive and a PAIN to delsolder so if you can find a replacement ysus for a reasonable price, i would buy it.

And yes, you wont be able to unhook one buffer at a time because they appear to be all on one board.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

The IPM failures, and the sparklies issue, are two reasons I stay away from these sets.

So,if I replace with a good board it may still have the sparklies issue?

Note I have never heard of a bad Y-sustain killing an LG buffer board, though I wouldn't rule out the possibility.

Are you saying it's probably a y-sus issue not a bad buffer?

What is the board number on your ysus? IPMs are expensive and a PAIN to delsolder so if you can find a replacement ysus for a reasonable price, i would buy it.

And yes, you wont be able to unhook one buffer at a time because they appear to be all on one board.

6871qyh063a is the board number. I've found it for $59 plus shipping without trying very hard.

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

So,if I replace with a good board it may still have the sparklies issue?

Yep... it's something to do with the plasma panel ageing. It's fixable, but requires new firmware.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Replaced the caps this afternoon. No luck.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Checked all of the voltages. They all look good. Both heat sinks on the YSUS board get warm to the touch when power on. The one heat sink on the ZSUS is also warm. There are no blown fuses that I can find. I'm not sure where to go from here.

Is there a way to positively confirm a good or bad Y-SUS short of swapping it out?

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

So, after sleeping on it for the night, I'm wondering if I have either

a) a bad panel

b) a bad Y buffer board

I think I remember seeing somewhere on here that you can test the YSUS with an O-scope. I can get my hands on one, but I'm a few years removed from actually using one.

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

I've never heard of an older gen LG with a bad panel. So I'd rule that out.

We DID have someone here with intact fuses, but no picture, good sound. Was the IPM.

The waveform is about +/-300V so make sure you have a scope which can handle that. Bandwidth of 20 MHz MINIMUM, recommended 100 MHz.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

I've never heard of an older gen LG with a bad panel. So I'd rule that out.

We DID have someone here with intact fuses, but no picture, good sound. Was the IPM.

So you'd rule out the Y-buffer too? Out of curiousity, what would a good Ysus and a bad Ybuffer do?

The waveform is about +/-300V so make sure you have a scope which can handle that. Bandwidth of 20 MHz MINIMUM, recommended 100 MHz.

OK, I'm heading over to take a look at the O-scope this afternoon.

[rayrod81]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

A 42" LG with a good Y-sus and bad buffer would give you a picture with random, colored vertical lines spread out across the screen.

[mattpd]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Checked all of the voltages. They all look good. Both heat sinks on the YSUS board get warm to the touch when power on. The one heat sink on the ZSUS is also warm. There are no blown fuses that I can find. I'm not sure where to go from here.

Is there a way to positively confirm a good or bad Y-SUS short of swapping it out?

The fact that the heat sinks are warm on ysus may mean it is ok. When mine failed, the heat sinks were cold. Yours could be different.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

Who knows, this one's got me scratching my head. Unless things take a turn for the better, I don't see a lot of plasma tvs in my future.

[tom66]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

I like plasma TVs more than LCDs.

The older ones are harder to fix, but the newer ones are pretty easy. Usually just a shorted fet or something. I've had better success fixing plasmas than LCDs, 8/10 successfully fixed (and that last one was because I broke the panel!) whereas LCDs I typically get 70~80% success ratio.

[johnboy1313]

Re: First plasma, LG 42PC5D. Sound but no picture. Help me make sense of this.

I got a scope today. Tektronix TDS 210. I need to download the manual and see what this thing can handle. I also need to know where to hook it up and what to look for. Thanks