LG Plasma 42PG6010

[ReeceyBurger123]

Re: LG Plasma 42PG6010

Zbias can run that low and the set still work. Test the Zsus Igbts for short circuit.

[ocf]

Re: LG Plasma 42PG6010

I started testing the IGBT's on the Zsus, first in circuit which gave me weird readings. I took one out of circuit and its still seems to be acting weird.

Chip is 30F122 according to datasheets -

Pin 1- Gate
Pin 2 - Collector
Pin 3 - Emitter

even with the IGBT I selected out of circuit when I put + from DMM on to gate I don't get any voltage drop between Pin 2 and 3.

I tried all other combinations and still get nothing resembling the readings I should be seeing. No complete shorts either.

Am I testing these wrong? Does my DMM have enough voltage to turn the gate on? I'm unsure where these values are in datasheet.

[vinceroger69]

Re: LG Plasma 42PG6010

this is a good video on how too test them
https://www.youtube.com/watch?v=_Ygmbfw-9XE

[ocf]

Re: LG Plasma 42PG6010

Watched it last night, great video.

I've removed 5 IGBT's from board so far.

First four were all from same heatsink, none test as they should.

Using DMM diode mode

1. Place COM Probe on emitter and +V on Collector - Open Circuit
2. Place +V Probe on gate for 2 seconds
3. Place COM back on emitter and +V on Collector again - DMM shows a momentary reading and then back to open, similar to when a small cap discharges too quick for the meter to get a reading.

Any advice welcome guys. I've Tested 5 IGBT's, 4 from one heat sink and one from separate one on the other side of the board. All showing this same test result.

[vinceroger69]

Re: LG Plasma 42PG6010

maybe try a diffrent multi meter see what readings you then get what meter are you using now?

[ocf]

Re: LG Plasma 42PG6010

[ocf]

Re: LG Plasma 42PG6010

Just tested the IGBT's with another meter using a brand new battery, No difference, not even seeing the momentary connection I was seeing with the other DMM

I used both DMM's to test each other and see how much voltage they put out in diode measurement mode. The UT33B I pictured puts out 2.97V and the second around 2.7v

[vinceroger69]

Re: LG Plasma 42PG6010

i wonder if that voltage is high enough to turn the igbt on? maybe budm will know/advise im sure i read they need about 3.3 volts but cant find where i read it now.

[ocf]

Re: LG Plasma 42PG6010

I was thinking something similar, I will check datasheet and report back

[ocf]

Re: LG Plasma 42PG6010

I've highlighted the IGBT I'm testing below. I don't see any reference to gate voltage, gate threshold voltage is supposed to be denoted by VGE which I cant find any reference to
https://postimg.org/image/cqh9w6o23/

[dick_barton]

Re: LG Plasma 42PG6010

I think you may find one of these useful. Diode, resistors, caps, transistors, mosfet tester. Tends to give slighly higher readings on ESR than my Dick Smith ESR meter but I find the unit very useful.

http://www.ebay.co.uk/itm/LCD-Transi...-/301672309369

[ocf]

Re: LG Plasma 42PG6010

Seems like the PDF I was looking through wasnt great, I found a proper datasheet for the IGBT.

Images below are stats for the IGBT, can anyone explain where the threshold gate voltage is below.

Seems like "gate emitter cut of voltage" is about right. Whats the Min/Typical/Max about?

[dick_barton]

Re: LG Plasma 42PG6010

The Gate Emitter cut off voltage is not fixed but can be anywhere between 3.0V to 5.0V although it is typically around 4.5V
That's the voltage at which the device switches off.

[vinceroger69]

Re: LG Plasma 42PG6010

so in regards to post 47
Just tested the IGBT's with another meter using a brand new battery, No difference, not even seeing the momentary connection I was seeing with the other DMM

I used both DMM's to test each other and see how much voltage they put out in diode measurement mode. The UT33B I pictured puts out 2.97V and the second around 2.7v

do you think the multi meters have a too low voltage to turn the igbts on too test them?

[dick_barton]

Re: LG Plasma 42PG6010

If your meter puts out 3.0V in diode mode then I suspect it is to low.


Edit
See post #25
https://www.badcaps.net/forum/showth...t=55047&page=2

[ocf]

Re: LG Plasma 42PG6010

I used a DC power supply to turn on the IGBT's they test ok so far.

I found three 51N25 N Channel mosfets that I also removed and tested datasheet below -

http://www.datasheetspdf.com/PDF/51N25/955427/1

One shows same test characteristics as the IGBT's I've tested so far, the other two still show a voltage drop drain to source after I bridge gate.

Am I testing the MOSFET correctly?

The remaining IGBT's are all on the center heatsink, very difficult to get them unscrewed from it. I might try taking the whole heatsink off.

Can I not narrow down which IGBT's deal with the ZBias?

[dick_barton]

Re: LG Plasma 42PG6010

I not sure how you are testing them but if you are fully switching on the 51N25 then with a 60 milli-Ohm "ON" resistance there should be no noticable voltage between Drain and Source. Basically it should look like a short circuit.

[ocf]

Re: LG Plasma 42PG6010

I have a DC power supply built in to the hot air rework station, 0-30v 6amp

1. Check continuity between drain + Source COM lead on Source +V on Drain - Open circuit

2. I put 4.2v DC on the gate pin of the FET

3. Check continuity between drain + Source COM lead on Source +V on Drain - DMM Showing a reading of 700-800

I believe this DMM shows no decimal place on the MV scale so I just see 3 digits.

Two of the FETS were showing 1200-1400 using same test.

[ocf]

Re: LG Plasma 42PG6010

I'm going to buy the Transistor Tester you suggested, help get these damn things checked out quicker. Still good to learn the manual way and I appreciate the help Dick Barton

[ReeceyBurger123]

Re: LG Plasma 42PG6010

Lg have a habit of blowing 51n25 transistors open oddly.