LG Plasma 50PC1DR- Y-SUS Issues

[cheebster]

Ok, i got 3 defective plasmas here i've bought for a few bucks to play with. I'm an IT tech, but i love electronics.. trying to push the limits of what i can fix.

I think i did my homework of reading pages and pages and trying to figure out what's wrong on there, but so far i'm still stuck.

! Plasma 1 : LG 50PC1DR. This one has sound, but the screen flickers (tries to fire up). I can hear the y-sustain board clicking.

Plasma 2 : LG 50PC3. This one powers on but image is pinkish with snow on it, it really doesn't look good. I see a no signal logo floating around that leaves some marks of it when it changes position. Here is a picture of what it looks like, see image attached. Only thing ive seen on the y-sus are the 2 resistors also shown on attached image, replaced them from another board. No change !

Plasma 3 : LG 50PC3. This one has sound, with no screen. It tries to fire up also. I can hear the y-sustain board clicking.

What i've tried so far.. swapping the y-sus boards between the different units to see if the behavior changed. That didn't lead to much..

After, i've figured out after reading that the IPM(s) were at fault, maybe. So i managed to pull out some of these YPPD-J015, YPPDJ016 without damage. However, doing some meter testing, i don't see any shorts. Does that mean they're good ? I seriously don't know !!

I'm really looking for advice here, i don't know where i'm going. Thanks !!!!

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

The second one is either Z-sustain or more likely someone who has tweaked around too much with the adjustments on the Y-sustain and messed it up! It should be fixable with a multimeter.

The other two are likely Y-sus faults. The IPMs can be replaced at approx $40 each. No, they do not always go short when they fail - someone on here before (can't find the post right now) had the same problem, and replacing the IPM solved it.

Adjustment procedure for TV #2:
- Test Vs voltage. It will be indicated on the panel sticker - around 190V. Check it is within 0.5V of this. If it is not, adjust it until it is.
- Test Va voltage. Use the same procedure, around 65V. Adjust it until it is within +/-0.5V.
- Test Vsc voltage. This is usually across a resistor on the Y-sus; post a larger image of the Y-sus and I'll point it out. Typically 190V. Adjust to within +/-1V.
- Test -Vy voltage. Similar to Vsc but negative, around -190V. Adjust to within +/-1V.

If all of these are in spec, suspect Z-sustain.

If not - Now you will likely have an acceptable picture but with some sparklies (flickering picture) or image retention - here is where it gets tricky. Basically, the get rid of sparklies, turn SET_UP clockwise until they either reduce or get much more significant. If they get more significant go the other way. Then, try tweaking SET_DN if you still can't get a perfect picture.

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Hi tom66. Thanks for the reply, first !!!

I was wondering, since there's 2 IPM.. when ppl here say, replace 'the' ipm.. They're talking about the YPPD-J015, which is the SUS IPM ?

Is that one more prone to failure than the other one, the J016 ER IPM ?

Here is a better picture attached ! I adjusted a little bit the VS and VA, but it was within spec.

Do you have a clue what caused those 2 resistors to burn on the YSUS ?

Thanks !!!

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Um.. Quick reply here. I really need to know how to properly test VSC and -YV. I see 4 tests points on the board, 2 called VSC TP and 2 called -YV TP. Do i need to test between the 2 of them ? I get 143V between the 2 VSC and nothing between the 2 -YV..

Not sure im testing stuff properly though

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Generally the "SUS" IPM fails more often, but you may have to replace both, which is difficult/expensive... I don't have enough experience with LG plasmas to say whether both need replacing or just one. A better option may be to find someone selling used Y-sustain boards, or someone rebuilding them.

Can't see any burnt components on your Y-sus. Can you highlight them?

On older LG plasmas, the -Vy was tested across a resistor. Let me check if I can get the service manual which explains where to check.

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

This is another y-sus board i have here from 1 of the 3 tv's on which i removed the IPM's.

The 2 burned resistors on tv #2 are just left of the big heatsink, marked 100, R75 and R79.

I have no problem replacing the IPM's ! I can remove one in 15 minutes now.

What i did, is i used a small vacuum called 'shark' from canadian tire i had no use for, just attached that instead of the small red balloon on the 45w desoldering irons. I put the iron on the pin, heat it up a bit more with a small torch and vacuum the solder. Takes a few seconds per pin, but does a perfect job

Kind of homemade desoldering gun.. will keep that thing assembled ! I've looked for a hakko gun, but 200$ isn't justified for the few desoldering jobs im doing.

here is the service manual; http://uploaded.net/file/6ok0h3oo

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Okay, i've left this #2 going with the weird screen while i was searching... it popped, and shutted down. Now it won't fire up, it just goes black when i try to start the tv.

I'm gonna pull back YSUS and see if anything popped !

Well, i don't see anything that burned. Don't see any shorts on the IPM's.. Where to look now

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Check the fuse on the board. Looks like you will be looking for three Y-sustains if you can't find the IPM or find it costs too much...

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Ok, found that one. One of the fets, the one on the right black heatsink, is shorted ! Prolly the cause of the 2 burned smd resistors. So far, one ES1G smd diode and 1 102 smd resistor open in that area. I hope not too much is burned, but the FET was def. shorted and caused a little damage there.

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

I see the burnt resistors you talk about. Those control SET UP which manages the initialisation of the PDP. If that goes wrong those symptoms (lots of misfiring pixels) fit well.

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Swapped 2 resistors, 1 fet, 2 diodes from donor board. Wondering if i should try it now :/ Checking to see if i missed anything..

Well, after putting it back in the unit, the 2 100 big resistors near the silver heatsink burned again. It seems they're acting like a fuse with my issue, they're the first to go...

I've seen the magic smoke, and those 2 resistors burned again. Is there something else shorted that i'm missing to get them to burn ? I was also wondering if it could be an mis adjustment of one of the pots there, RAMP_UP, VSET_DN, -yv, VSC ?

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Are there any other FETs connected to those resistors? Check from the end of the resistors to ground (metal frame of TV) and see if there appears to be a short.

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

I see no shorts to gnd on either side of the resistors, but from one side of the resistors it goes to the middle pin of the 59N25's (the ones on the smaller heatsink).

I was wondering, those 2 fets on the black heatsink, do they need to be a matched pair ? I've replaced a w9nk70z by a k2673 from another board, same location. Is that ok ?

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

As long as the current rating is GREATER or EQUAL, the voltage breakdown is GREATER or EQUAL, the RdsON is LESS or EQUAL and the gate charge (Qg) is LESS or EQUAL, then the FET should be OK.

Check the FET is not shorted on any pins - check for resistance between each pair of the 3 pins, e.g. 1-2 1-3 2-1. Should be greater than 20 ohms for each.

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

I don't see any shorts on the 2 fets on the black sinks.

The fuse FS3 was open, and so the resistors, i just finished removing the J016 IPM, no joy. All seems fine there... :/

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

But it's still burning those resistors?

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Yes

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

I'm really wondering why those IPM modules goes bad at the first place.. heat ?

Looking at some of them, nothing seems wrong doing DMM test, well nothing obvious..

If they are considered items that wear over time, what is getting older on these, those small little plates with bonding wires on them ?

I have a few covered with rubber, i'm wondering how to uncover the rubber, heat maybe ?

I've tried scraping, but i don't wanna break components, since i don't even know which of the ipm's are good and which are not !

Ah, tv repair, not that easy !!!!

[tom66]

Re: LG Plasma 50PC1DR- Y-SUS Issues

I'm really wondering why those IPM modules goes bad at the first place.. heat ?

Looking at some of them, nothing seems wrong doing DMM test, well nothing obvious..

If they are considered items that wear over time, what is getting older on these, those small little plates with bonding wires on them ?

I have a few covered with rubber, i'm wondering how to uncover the rubber, heat maybe ?

I've tried scraping, but i don't wanna break components, since i don't even know which of the ipm's are good and which are not !

Ah, tv repair, not that easy !!!!

They were poorly designed by LG, and they began failing after a few years. VERY common issue to have an LG plasma with no picture but OK sound. They shouldn't need replacing if they were well sized, but they weren't.

The potting compound (rubber) is very difficult to remove. Maybe you could install a suspect good IPM in a board with a suspect bad IPM? If that one ticks away, then maybe it's not the IPM, but something else...

TV repair can be tricky but it's really rewarding to take something from the dump and bring it back to life. Trust me - done it 30+ times!

[cheebster]

Re: LG Plasma 50PC1DR- Y-SUS Issues

Okay. Now what is likely to cause those resistors to burn on the y-sus ? I seriously don't know what else to check on that board. I guess i missed something, but can't find out!!