LG 42pt85 plasma TV turns on but has no picture

[Dannyx]

Re: LG 42pt85 plasma TV turns on but has no picture

Yeah, I remember those. Those are what I watched when I had that first dead IPM I mentioned - transistors are too expensive to justify the effort/risk though, at least locally, since they would probably be relatively inexpensive online somewhere. I wouldn't do this for a client - only if it were my TV and had the time to waste. I think it's getting a new Y sus or going in the bin. I believe the guy said he didn't have bad fuses either, so it could be similar to my case.

[R_J]

Re: LG 42pt85 plasma TV turns on but has no picture

Well, type IPM Repair into google I have never done this https://www.youtube.com/watch?v=CARdm0o0FyM
https://www.youtube.com/watch?v=UfMOFi7aQN8

[Dannyx]

Re: LG 42pt85 plasma TV turns on but has no picture

I guess there's no point in removing it - there's no "repairing" an IPM from what I gather.

[freakaftr8]

Re: LG 42pt85 plasma TV turns on but has no picture

The 18v is never 18v in these LGs.. always 15v what I've always encountered. Sounds like your IPM is wasted

[Dannyx]

Re: LG 42pt85 plasma TV turns on but has no picture

Those resistors checked ok.

I also get 15v out of these regulators pictured, despite the silk screen on the bottom saying 18v. This happens when I supply 5v to the 5v pin on the main connector. The regulators ARE 15v regulators, so they operate fine.
IPM looks more and more dead at this point.

Also found where -Vy should go (resistor checks OK), but haven't measured it yet.

[freakaftr8]

Re: LG 42pt85 plasma TV turns on but has no picture

passive 8 pin resistors that carry control board ribbon signals in to the ysus. On the ysus inline with the ribbon input

[Dannyx]

Re: LG 42pt85 plasma TV turns on but has no picture

Also check RA1 to RA8 for resistance. These are passive. Ive had those go open too. But usually that would not shut the VS down..

What are RA1-8 ? Sorry, don't have the board in front of me right now and my photographic memory's not all that great

[freakaftr8]

Re: LG 42pt85 plasma TV turns on but has no picture

Also check RA1 to RA8 for resistance. These are passive. Ive had those go open too. But usually that would not shut the VS down..

[Dannyx]

Re: LG 42pt85 plasma TV turns on but has no picture

Just to recap, you have check all the diodes on the board? Resistors too? Those flat I believe 100 or 200 style resistors like to open.. Usually they are paired

Diodes yes, resistors no, at least not extensively. I did check some of the larger SMD ones, since it was easier to do, but haven't gone all out to check every last bloody one on there

[freakaftr8]

Re: LG 42pt85 plasma TV turns on but has no picture

Just to recap, you have check all the diodes on the board? Resistors too? Those flat I believe 100 or 200 style resistors like to open.. Usually they are paired

[Dannyx]

Re: LG 42pt85 plasma TV turns on but has no picture

Removing the IPM module alone makes me sick. Combine that with the fact that it's cast in gel and with the probability it's not the issue and it makes me hesitant to even struggle to pull that IPM out...probably easier to go with a replacement Y-sus, though that's also a gamble since the issue could also be somewhere else. I'm leaning towards a faulty Y-sus myself TBH. Fixing it would be awesome tho I HAVE fixed some before, but there were obvious shorts and dead components.

[Dannyx]

Re: LG 42pt85 plasma TV turns on but has no picture

The meter doesn't have time to refresh fast enough to capture it - I tried it The only way I can try it is to remove the ribbon like I said, which makes it stay on...this is what's actually puzzling the hell out of me. There's probably an error signal or something that's sent by the Y-sus via that flex cable that causes it to shut down.

[freakaftr8]

Re: LG 42pt85 plasma TV turns on but has no picture

I did have that fault in a different TV (think it was called Platinum or something like that....anyway), that had a dead IPM but at least was very obvious: fuse was blown on Y-sus and the Vs pins of the IPM were shorted to GND. Not this one though: fuse is ok and there are no shorts, unless IPM somehow failed OPEN or something's messing up inside....

Its happened to me before.. Not quite as common, however it happens.. Ive had DC regulator issues within an IPM module fail as well causing this with no blown fuse.

[tom66]

Re: LG 42pt85 plasma TV turns on but has no picture

You can try checking it before it shuts down

[Dannyx]

Re: LG 42pt85 plasma TV turns on but has no picture

You may have a short on the IPM module.. Very common.

I did have that fault in a different TV (think it was called Platinum or something like that....anyway), that had a dead IPM but at least was very obvious: fuse was blown on Y-sus and the Vs pins of the IPM were shorted to GND. Not this one though: fuse is ok and there are no shorts, unless IPM somehow failed OPEN or something's messing up inside....

[freakaftr8]

Re: LG 42pt85 plasma TV turns on but has no picture

You may have a short on the IPM module.. Very common.

[Dannyx]

Re: LG 42pt85 plasma TV turns on but has no picture

I think I recall seeing Vy across a large resistor on the Y-sus, but like I said, I can't convince the TV to stay on, except by disconnecting that ribbon between the control board (which I mistakenly call a T-con) and the Y-sus.

[tom66]

Re: LG 42pt85 plasma TV turns on but has no picture

Vsc, -Vy are marked on the Y- and Vzbias on the Z-sustain
You should be able to see them

[Dannyx]

Re: LG 42pt85 plasma TV turns on but has no picture

Very good material here, albeit for a different model. I'm mostly interested in learning as much "plasma lingo" as possible so you guys don't have to struggle and waste time explaining it to me. VSC and VY are both somewhere on the Y sustain apparently. Given that Vs shuts off, even with the Y sus in place, I doubt I'll get either of those.

[Dannyx]

Re: LG 42pt85 plasma TV turns on but has no picture

Oh, is VSC like the "t-con" ? If yes, then I believe that's OK: there's a couple of regulators like 5v, 3.3v and 1.8v on it and they all checked fine. Even tried powering it with an external 5v adapter (disconnected from the TV of course) and it turned on, generated those voltages and began flashing the green LED in the bottom corner of the board, so I BELIEVE it's fine. One thing I noticed is that there's a row of 4 LEDs slightly off-center and only 3 of those come on. Without a manual to tell me what they represent, it's hard to tell if that's an error or it's normal. Can't believe the most crucial information is not in that manual I got....
UPDATE: ok, no VSC is not that.....but at least now I checked another thing off the list FAAAAAIL !