LG 50PQ20 Plasma no pic/no sound

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

I was mistaken. When I took the back back off, the same two resistors on the Z-sus were getting fried. I just didn't see any smoke :-( So it has something to do with the two sus boards are connected to each other

[tom66]

Re: LG 50PQ20 Plasma no pic/no sound

Can we see a pic under near those resistors?

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

I'm fairly certain that the problem is with the Y-sus board due to the fact that I replaced the Z-sus board and this only happens once the Z & Y are connected to each other and it's powered on

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

OK I'm fairly certain I found the culprit. After doing a little youtube, I present for your opinion, the burned buffer.
Seen as how I've been told by my s/o that "I am not allowed to spend any more $ on this until I can prove it works" I'm thinking I'll either find those two chips on another plasma project I have or, can I just remove that half of the buffer and half the screen should work?

[tom66]

Re: LG 50PQ20 Plasma no pic/no sound

Pretty toasty! I had a quick look at the pictures but got sidetracked... It looks like they're part of the combined ERC, and a failure on the Y-sus could damage them. I guess it's possible for a buffer to do the same but it seems far-fetched to me. Is the failure isolated to just those two resistors? You should be able to run the TV with one buffer removed though the picture may not work depending on the design.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

So I tried it with that half of the buffer removed and I didn't get any pic (which doesn't surprise me due to the state of the Z-sus board), but I also didn't have any problem with the resistors heating up. I need to find some resistors to replace the fried ones and then we'll see what happens. I'll update you when I do
Yes the failure is isolated to those two resistors on the Z-sus. IDK if it matter, but they are located fairly close to where the Y-sus connects

[tom66]

Re: LG 50PQ20 Plasma no pic/no sound

I would suspect a shorted buffer IC myself, see if you can trace where those resistors connect.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

The fried resistors on the Z-sus trace to pins labeled ER_COM

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

One other question. I can't see the 3rd band on the resistors that I need to replace, but I can faintly make out it's either yellow or gold. Do it think they are 100 kohm or 1 ohm?

[tom66]

Re: LG 50PQ20 Plasma no pic/no sound

I'm going to say 1 ohm by where they are located.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

I looked at a google image and it appears that the line I can't see is actually black, which would make it 10Ω. Does that sound correct & what about wattage? Also, what were you referring to as "ERC?"

[tom66]

Re: LG 50PQ20 Plasma no pic/no sound

ERC is energy recovery. The panel is a large capacitor, so it is resonated with an inductor, to recover the energy lost during the sustaining process. This newer design we are seeing in some plasma TVs combines both boards' ERC into a single circuit; older designs used separate ERC for each board. 10 ohm to me, that sounds a little too large, I'm not sure what to make of that.

[tw2005]

Re: LG 50PQ20 Plasma no pic/no sound

I think you'll find they're 10ohm but in parallel expecting 5ohms across them. Broad guess but maybe 1-3W and wirewound?

Are they completely burnt out or have you measured them?

looks like the PQ20 & PQ30 SUS boards could be closely related, at least that section of the boards looks the same. The training for the PQ30 shows how to power up with just the zsus if you want to prove it's good.

I've got a ZSUS from a later PJ350 and it has 3 x 20ohm in parallel giving 6.7ohms in a similar part of the cct.

I had a similar situation with similar low ohm resisitors(SMD) burning on an old PX5D thinking it was a bad Z but was a bad Y causing it. Most frustrating.

EDIT: I've added a spec sheet just as an example. The diameter is the only clue but what brand?? 3.5-6.5mm 1/2W - 3W with a 1mm tolerance.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

I think you'll find they're 10ohm but in parallel expecting 5ohms across them. Broad guess but maybe 1-3W and wirewound?

Are they completely burnt out or have you measured them?

looks like the PQ20 & PQ30 SUS boards could be closely related, at least that section of the boards looks the same. The training for the PQ30 shows how to power up with just the zsus if you want to prove it's good.

I've got a ZSUS from a later PJ350 and it has 3 x 20ohm in parallel giving 6.7ohms in a similar part of the cct.

I had a similar situation with similar low ohm resisitors(SMD) burning on an old PX5D thinking it was a bad Z but was a bad Y causing it. Most frustrating.

EDIT: I've added a spec sheet just as an example. The diameter is the only clue but what brand?? 3.5-6.5mm 1/2W - 3W with a 1mm tolerance.

I was looking at the LG man about checking Z-sus board but I know the resistors are fried (the dig meter climbs to almost an ohm then reads like there's nothing)
I'm fairly certain it's the Y-sus and buffer board. I'm gonna grab an old plasma I can cannibalize to see if there are any parts I can use, then I'll report back

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

I don't think I'm going to be able to fix the Z-sus board, but I did make a lil bit of progress. With the Z installed but no power from the y and the one bag buffer removed, I almost had a heart attack when suddenly I had sound So what say you wise men, if I get another Z and the buffer boards, do you think it'll work?

[tom66]

Re: LG 50PQ20 Plasma no pic/no sound

There is a good chance. You should be able to run it without the Z-sus. You'll get a really poor picture (purple tinted usually), but this'll then help because you know you just need a new Z-sus and that there are no further problems.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

W/O the Z-sus and minus 1/2 the y buffer I'll still get a picture?

[tom66]

Re: LG 50PQ20 Plasma no pic/no sound

Depends on the design. I don't think that'll work on this set unfortunately, you do need both buffers installed, but I'm not 100% on that.

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

I hope not, as I didn't get any picture. I'm ecstatic about getting sound though. That should indicate I've isolated the problem, correct?

[pk7tanner]

Re: LG 50PQ20 Plasma no pic/no sound

Can anyone tell me what the process is for checking my ysus (before I put in my new buffer board and repaired zsus)? What are the voltages ect.