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

[johnboy1313]

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

Can't see the pictures but you're usually looking for a test point marked "Waveform". Can you use Manage Attachments to upload higher res images in case it is named something else?

I'll have to look into the higher res images. Right now I can't even load pictures to the site. I've had to resort to using photobucket.

[johnboy1313]

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

I would take a DMM real quick and probe around the y and z board looking for shorts. I've had 3 of these IPM failures and they all failed short to gnd.

You can also remove the y and z boards, the IPM pins stick through the back and should be labeled. If you measure a short from one of the voltages to ground you know its bad.

I wouldn't recommend trying to change the IPM unless you have a good heat gun, just replace the whole board

Wouldn't there be blown fuses if something was shorted to ground? Both y and z sus boards get warm to the touch when the unit is powered on.

[Cosmo66]

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

I would take a DMM real quick and probe around the y and z board looking for shorts. I've had 3 of these IPM failures and they all failed short to gnd.

You can also remove the y and z boards, the IPM pins stick through the back and should be labeled. If you measure a short from one of the voltages to ground you know its bad.

I wouldn't recommend trying to change the IPM unless you have a good heat gun, just replace the whole board

[tom66]

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

Can't see the pictures but you're usually looking for a test point marked "Waveform". Can you use Manage Attachments to upload higher res images in case it is named something else?

[johnboy1313]

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

Where am I actually connecting the leads of this scope? What am I looking for? What am I setting the scope to?

[tom66]

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

Using a 10X probe with a 400V rating makes the signal only 40V at the scope, so you can use the oscilloscope with it. My Rigol is 300V rated but can survive a 1000V transient, so brief overvoltage is usually fine. Just either use a 10X fixed probe or be very careful not to move the switch from 10X to 1X.

[johnboy1313]

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

I borrowed it from a friend at work. Unfortunately it is only rated for 300V max. I found an older (early 90s) meter/scope on Craigslist that I might buy for $100. According to the manual I found online its capable of inputs up to 400V and 1Ghz

[tom66]

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

That is actually a pretty nice scope! Only limitation is its memory is I think 2.5k samples, but that's only useful if you want to look at several subframes. With most plasmas, all you need to see is if a particular waveform is there. Just make sure you use a 400V rated (or more) 10X probe with it. You do not want to blow up the input amplifier/attenuator section! Turn a dual channel scope into a single channel one . How much did you pay for it, if you don't mind me asking?

[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

[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.

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.

[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.

[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.

[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.

[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.

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.

[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.

Replaced the caps this afternoon. No luck.

[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.

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.