LG 42PC3D Bad Z-Sus IPM ?

[mmartell]

What confuses me is there are no blown fuses and all the voltages are there and in spec. The ipm heatsink is cold. There is a short registering between Sus_Out and ER_Up_Out/ER_Dn_Out but I've read these are shorted on the board anyhow.

When the zsus is removed the pic remains the same except there is no random sparkly noise and strobing as there is when the zsus is in.

Is this classic ipm failure or should I be looking at logic signals from the control board ?

[mmartell]

Re: LG 42PC3D Bad Z-Sus IPM ?

Gentle nudge.

[tom66]

Re: LG 42PC3D Bad Z-Sus IPM ?

There is a short registering between Sus_Out and ER_Up_Out/ER_Dn_Out but I've read these are shorted on the board anyhow.

They aren't supposed to be shorted...

[mmartell]

Re: LG 42PC3D Bad Z-Sus IPM ?

This is where i read it. It's for the stk795-518 but I can't imagine it would be any different. He doesn't explain it any further though.

http://blog.coppelltvrepair.com/2011...m-for.html?m=1

[tom66]

Re: LG 42PC3D Bad Z-Sus IPM ?

There should be a diode drop (0.7V) in REVERSE across ER_UP_OUT to SUS_OUT, but no short.
Check on your Y-sustain to confirm, if you like.

[mmartell]

Re: LG 42PC3D Bad Z-Sus IPM ?

Thanks tom will look for ipm replacement.

[tom66]

Re: LG 42PC3D Bad Z-Sus IPM ?

I think the confusion comes from SUS and ER. ER is different to ER_UP_OUT/ER_DN_OUT.

[mmartell]

Re: LG 42PC3D Bad Z-Sus IPM ?

Ok I had a closer look. I missed VER which is probably the ER I was looking for. I have no shorts and all voltages are present. There is a slight ticking from the IPM about once a second with other beats tossed in occasionally. I measured the test points from the control board and all had voltages except one labelled "OE" but since I don't know what that is I can't say it's significant.

Not sure how common it is for the IPM to fail in this way but with everything else checking out I guess that's what it is.

[tom66]

Re: LG 42PC3D Bad Z-Sus IPM ?

It's pretty common for the IPMs on these to "tick" when bad.

[mmartell]

Re: LG 42PC3D Bad Z-Sus IPM ?

I looked for a replacement and they mostly appear to be pulls so I found a used board which is *supposed* to be working.

So now I thought lets get this ic off the old board anyway, but even with a paint gun I couldn't seem to get enough heat to lift it. Can't take off the heatsink because of the way it's mounted.

Or can you ?

Measured out where the screws were and drilled some 1/4" holes and removed the screws and the heatsing then lifted the ic with alot less heat. Don't think I drilled through any arteries but can't test without installing a new ic.

[mmartell]

Re: LG 42PC3D Bad Z-Sus IPM ?

Had a look at the ipm itself. These things look fairly simple, why don't people undertake repairing them - those that don't blow up I mean, mine still looks like new.

[tom66]

Re: LG 42PC3D Bad Z-Sus IPM ?

The magic in the IPM happens in the hybrid module bonded to the back of that PCB. You can see the bond wires. They go to high-power IGBTs. Those are what fails on these IPMs.

[aaronwt6]

Re: LG 42PC3D Bad Z-Sus IPM ?

I looked for a replacement and they mostly appear to be pulls so I found a used board which is *supposed* to be working.

So now I thought lets get this ic off the old board anyway, but even with a paint gun I couldn't seem to get enough heat to lift it. Can't take off the heatsink because of the way it's mounted.

Or can you ?

Measured out where the screws were and drilled some 1/4" holes and removed the screws and the heatsing then lifted the ic with alot less heat. Don't think I drilled through any arteries but can't test without installing a new ic.

I've often wondered why they didn't put some holes in the board where the screws are or thread the IPM and have the screws go in from the top. It's nearly impossible to get those off without making somewhat of a mess of the board. I'd consider myself quite good at parts removal. I have all the right tools for the job and it's still difficult.

[Ltank]

Re: LG 42PC3D Bad Z-Sus IPM ?

What is the numbers on the tag on side of IPM? I have a new one that I tried to use I could send for free. PM me

[tom66]

Re: LG 42PC3D Bad Z-Sus IPM ?

I've often wondered why they didn't put some holes in the board where the screws are or thread the IPM and have the screws go in from the top. It's nearly impossible to get those off without making somewhat of a mess of the board. I'd consider myself quite good at parts removal. I have all the right tools for the job and it's still difficult.

Originally LG intended the boards to be non serviceable. You'd return the board to LG as a core.

The move to IPMs was intended to improve their reliability - indeed it worked well for the 42V4/V5 panels and I can't remember many 42X1 or 42X4A panels with IPM failure. However it appears that there was a manufacturing defect with the IPMs leading to their frequent failure on 42V6/V7 and 42X2/X3 (and the 50X1/X2/X3)

[vinceroger69]

Re: LG 42PC3D Bad Z-Sus IPM ?

didnt one member repair his own ipm? i cant find the post something about info he found on a polish forum?

edit found it!
https://www.badcaps.net/forum/showthread.php?t=34766

[mmartell]

Re: LG 42PC3D Bad Z-Sus IPM ?

That's a cool thread, thanks vince! My understanding of the electronics is just a little thin but I'm going to try and make sense of it..

tom thanks for that clarification. I'd come to believe those wires were there to wick the heat from the pcb directly to the heatsink lol. Btw, this panel is a v8.

[mmartell]

Re: LG 42PC3D Bad Z-Sus IPM ?

Replacement board is in and the picture is.. better, but... I can tell it's still not right. Less of a distinction between left and right sides of the panel but still over/under diffusion on the left side and the right is suffering from solarization and the pic is not sharp in any way.

The heatsink is stone cold. By contrast the heatsinks on the ysus are noticeably warm bordering on hot. I guess the IPM is defective ? Should the zbias control have an effect on the picture if the ipm is not active because it does..

[mmartell]

Re: LG 42PC3D Bad Z-Sus IPM ?

Contacted Payless and they have sent out another board. Will update when that gets here but I have my doubts - seems the zsus is such a common failure on the sets it's in that probably a high percentage of them on the used board market have defective ipm's.

This board was identical to mine in that the fuses were good and no shorts were detected between Gnd/Vs/ER/SUS but nevertheless it was not functioning.

[mmartell]

Re: LG 42PC3D Bad Z-Sus IPM ?

Update: replacement board is no good. I'm officially in the market for an IPM.