Samsung 50" Plasma, No Picture or sound

[RCFLYER]

Re: Samsung 50" Plasma, No Picture or sound

The Mosfets on the first heatsink from left in picture measures .2 ohms between the 2nd and 3rd pins. On the 2nd heatsink from left the second Mosfet has a measurement of .2 ohms between the 1st and third pin. None of the Mosfet were OL

[tom66]

Re: Samsung 50" Plasma, No Picture or sound

So they are all shorted?

This is going to be tricky, but you're going to have to desolder every single MOSFET and test it out of circuit, because there's probably just one on there which has failed.

[RCFLYER]

Re: Samsung 50" Plasma, No Picture or sound

The Mosfets on the first heatsink from left in picture measures .2 ohms between the 2nd and 3rd pins. On the 2nd heatsink from left the second Mosfet has a measurement of .2 ohms between the 1st and third pin. None of the Mosfet were OL

I tested the quoted section measuring ohms. I believe I was suposed to test in diode mode.
The 1st set of mosfet caused the meter (FLUKE 87V) to beep in any combination of pins. Same happens in the 3rd heatsinked mosfets.
I do get OL only in the 2nd set of mosfet when the leads are revearsed.

[RCFLYER]

Re: Samsung 50" Plasma, No Picture or sound

I'll probably order the Y-main board, and tinker with this one, parts might take longer to find. The # on the board I have is 50" U1 Drive YM PCB NO: LJ41-05905A Rev. NO: R1.15 . Does the board have to be the same Rev # or can a board of higher revision work?

[tom66]

Re: Samsung 50" Plasma, No Picture or sound

There is a failed MOSFET in the first or third section then. If you want to repair it, you'll just have to locate which one. If you have an 87V, you'll be able to switch it to a high resolution mode on ohms so you get .01 ohm resolution. If you then cancel the leads out (using rel), the reading with the lowest resistance is closest to the failed device.

[RCFLYER]

Re: Samsung 50" Plasma, No Picture or sound

I removed the 4 Mosfets from the first section. What should a normal reading be between certain pins. What reading between certain pins is considered bad. I don't read .3 ohms between ground and fuse anymore. It's about 562 Ohms.

[tom66]

Re: Samsung 50" Plasma, No Picture or sound

Anything lower than 30 ohms is definitely shorted. To make sure, connect all the leads together with a wire jumper, to discharge the gate, then check all pins: it should measure greater than 1 meg-ohm in all directions under ohms test. In diode mode, you should see a diode drop between two combinations of pins either way, but only if the first test is inconclusive do you need to perform the diode test.

[RCFLYER]

Re: Samsung 50" Plasma, No Picture or sound

Ist Mosfet reads OL any combination except when leads are reversed on pin 2 and 3m reading is 295k ohms.
2nd reads .7 ohms between 1&2,1&3, 02 ohms between 2&3.
3rd reads 72 ohms between 1&2,1&3, .3 ohms between 2&3
4th reads 136 ohms between 1&2,1&3 .2ohms between2&3
Board does not read .3 ohms between fuse and screwhole anymore.

[tom66]

Re: Samsung 50" Plasma, No Picture or sound

Did you short the pins as I instructed you to when testing these devices? Try and short the pins out just before you make the measurement, as the gate pin is extremely sensitive to any charge accumulating on it.

What's the part number on #2? Most likely this is failed. #3 and #4 might also be failed - it's possible one failure killed the others. (Best bet would be to replace them all, they aren't too expensive.)

[RCFLYER]

Re: Samsung 50" Plasma, No Picture or sound

I shorted all three pins before every measurement. Is it safe to say 3 of the four are bad.

[tom66]

Re: Samsung 50" Plasma, No Picture or sound

I shorted all three pins before every measurement. Is it safe to say 3 of the four are bad.

Quite likely. I'd replace them with those readings. What are the part #s? I'll try and find you the parts on Digikey - or equivalent replacements.

[RCFLYER]

Re: Samsung 50" Plasma, No Picture or sound

quite likely. I'd replace them with those readings. What are the part #s? I'll try and find you the parts on digikey - or equivalent replacements.

2 pcs, irfp4332 r844p 9y
2 pcs, rjh3044 8doe

[tom66]

Re: Samsung 50" Plasma, No Picture or sound

Well, the first ones are easy to get: http://search.digikey.com/scripts/Dk...Words=irfp4332

$4.29 each ouch, but they are very high performance devices...

The second ones are custom parts. The best place I could find them was here: http://hkkoson.member.seekic.com/pro...r/RJH3044.html but that's in China; this is also an option: http://www.utsource.net/ic-datasheet...4-1581384.html

I've heard this is compatible... http://www.fairchildsemi.com/pf/FG/FGPF50N33BT.html ... but wouldn't bet on it.

I had the same difficulty finding an RJH3044 for a Z-sustain board in a Samsung. I ended up replacing the Z-sustain because it was only £18. No luck here, though...

[RCFLYER]

Re: Samsung 50" Plasma, No Picture or sound

Thankyou very much TOM66 I will order the parts, and post how I did.

[RCFLYER]

Re: Samsung 50" Plasma, No Picture or sound

I removed and tested the 2 Mosfets (FBPF50N33) left on the third Heatsink, they were also shorted.

[tom66]

Re: Samsung 50" Plasma, No Picture or sound

I removed and tested the 2 Mosfets (FBPF50N33) left on the third Heatsink, they were also shorted.

Looks like a fairly catastrophic failure. There is also the possibility the buffer chips are shorted. If this is the case, it's very difficult to repair. But usually when these chips fry, they make nice holes in themselves and smoke everything up.

Check the continuity between red and black should measure higher than 500 ohms.

[RCFLYER]

Re: Samsung 50" Plasma, No Picture or sound

Looks like a fairly catastrophic failure. There is also the possibility the buffer chips are shorted. If this is the case, it's very difficult to repair. But usually when these chips fry, they make nice holes in themselves and smoke everything up.

Check the continuity between red and black should measure higher than 500 ohms.

It measures OL.

[tom66]

Re: Samsung 50" Plasma, No Picture or sound

It measures OL.

That's good then, the buffer ICs are most likely okay.

Seems like one MOSFET shorted out, and took the other three with it.

[RCFLYER]

Re: Samsung 50" Plasma, No Picture or sound

I received the new MOSFET's today. I'm ready to solder them in but I have a question. There was a rubber gasket between 2 of the MOSFET's and the heatsink. Should I leave it out and apply heatsink compound, or reuse the gasket. There was no heatsink compound with gasket.
Also can someone give any pointers on soldering them in. Should I screw them to the heatsink then solder?

[PlainBill]

Re: Samsung 50" Plasma, No Picture or sound

I received the new MOSFET's today. I'm ready to solder them in but I have a question. There was a rubber gasket between 2 of the MOSFET's and the heatsink. Should I leave it out and apply heatsink compound, or reuse the gasket. There was no heatsink compound with gasket.
Also can someone give any pointers on soldering them in. Should I screw them to the heatsink then solder?

Use the silicone heat transfer pad. Mount the transistors to the heat sink, then solder.

PlainBill