Troubleshooting LG Plasma

[DanFen]

Re: Troubleshooting LG Plasma

Tested the Mosfets and the IGBTs that had short in circuit, and the Rectifiers as well.

Mosfets and IGBTs were tested in the same method, i.e. tested on and off state.
Rectifiers were tested like normal diodes, got 0.4 reading on the good ones.

Does this make sense? I also wonder if I should get the other 4 that are still on the board and test?

[DanFen]

Re: Troubleshooting LG Plasma

Why do I still have continuity on the IGBT / FETs / Rectifer connectors (holes) on the board even with the components out of the board (although not all of them have this)? I also noticed that 2 of the 3 holes of these components are covered in metal, the other is just a hole.

[DanFen]

Re: Troubleshooting LG Plasma

I've ordered this diode, although I am not sure what else I can check I haven't individually checked the rectifiers/fets I've removed though.

[DanFen]

Re: Troubleshooting LG Plasma

The problem is, the markings on it are so faint I can't read them.

EDIT: I think it says UF4007

[DanFen]

Re: Troubleshooting LG Plasma

I've actually removed it altogether.

Did you lift one leg of the one with the bad reading too?

[tvtimmy]

Re: Troubleshooting LG Plasma

Did you lift one leg of the one with the bad reading too?

[DanFen]

Re: Troubleshooting LG Plasma

You're correct, removed one of them and it measured correctly.

But the other didn't, there's continuity from negative to positive, and reading when set to to diode mode shows 0.002.

Now this is a funny one (or funny because I've never seen it), cause the Cathode side has a long leg which seems to be connected to some other component which I am not able to see (it's hidden under the heatsink). I'm attaching an image.

Unsolder 1 leg and test again. Capacitors can cause funky readings.

[tvtimmy]

Re: Troubleshooting LG Plasma

Unsolder 1 leg and test again. Capacitors can cause funky readings.

[DanFen]

Re: Troubleshooting LG Plasma

No the ones I've checked are 2 legged. I've pointed them out on the photos.

Do the diodes have 3 legs? If so, the outer ones are connected and they will beep or read short. Test them center to an outer then center to the other outer.

[tvtimmy]

Re: Troubleshooting LG Plasma

Do the diodes have 3 legs? If so, the outer ones are connected and they will beep or read short. Test them center to an outer then center to the other outer.

[DanFen]

Re: Troubleshooting LG Plasma

So following that, I've checked diodes for short (in diode more + beep), and found 2 that "are shorted". I'm attaching 3 photos showing these diodes (one of the photos is a full view of the board).

[DanFen]

Re: Troubleshooting LG Plasma

So I got all of those which I found were shorted out of the board. I must say that I never had such difficulty with desoldering components out like I had with these!

Some feet of these components have a round circle around them, what does it mean?

What is the best way to proceed from here?

[DanFen]

Re: Troubleshooting LG Plasma

Thanks Is the testing of Mosfets and Rectifiers the same? Cause as you can see from the drawn diagram there is only one IGBT that is shorted, and from what I could find, these work a little bit different to Mosfets and Rectifiers.

The testing method is correct, if the IGBT measured shorted in circuit but looks good when out of circuit this means there is another IGBT or some other failed component.
Look at the traces to see what else could be the reason for the short.

[zape]

Re: Troubleshooting LG Plasma

The testing method is correct, if the IGBT measured shorted in circuit but looks good when out of circuit this means there is another IGBT or some other failed component.
Look at the traces to see what else could be the reason for the short.

[DanFen]

Re: Troubleshooting LG Plasma

Thanks I'm attaching a diagram with those that are shorted (marked with a C). I couldn't successfully read the part numbers of some of them.

I've already removed the bad RJP63K2 and according to a previous post, it seems to be good. I did it like so:

Continuity between Drain & Source: no continuity (and I am guessing this is good?).

Then I've tested the On/Off state by charging the capacitor. I did this with the multi-meter by:

1. Holding the negative on the Source, and touching the Gate with the positive lead.
2. Then I moved the positive lead onto the Drain to test and got no connection.

Just want to make sure that the above testing method is correct for all the shorted components?

IGBTs might be connected in a parallel so you'd want to remove one by one and test out of circuit until you find that the board is no longer shorted.

[zape]

Re: Troubleshooting LG Plasma

IGBTs might be connected in a parallel so you'd want to remove one by one and test out of circuit until you find that the board is no longer shorted.

[DanFen]

Re: Troubleshooting LG Plasma

So I guess the next step is to remove all IGBTs/FETs that resulted as bad in the continuity test and test them individually?

[DanFen]

Re: Troubleshooting LG Plasma

OK, so at least I'm on the right track. But this doesn't necessarily mean that the IGBT/FET is damaged right? Am I right to say that other components might be causing the short to ground on it? And if the answer to this is positive, that means that the IGBT/FET testing out of circuit might have good results... meaning, the IGBT/FET can be good?

Yes, that's the right way.

[tvtimmy]

Re: Troubleshooting LG Plasma

Yes, that's the right way.

[DanFen]

Re: Troubleshooting LG Plasma

Can do that, for the sake of learning

What I'm not sure about is, if I was testing them correctly while in circuit. I was setting the meter to continuity mode (beep mode) and alternating between all 3 pins. So S with G, S with D, and D with G, and see if it beeps. If it beeps I was noting it as short. Is this the right way or am I messing it up?

Thanks.

Sometimes the igbt's don't all go bad. You will have to remove them one at a time, noting which ones go where, until the shorts all go away.