Samsung PS50a410

[nickdablack]

Re: Samsung PS50a410

Where is DP802 on the PSU? Seems like that FET took out a few other things with it.

Its right next to the fet. Short across the fet as well so it might be the fet not the rectifier. Will look tonight.

[nickdablack]

Re: Samsung PS50a410

Pulling out components 1 at a time but there is still a short on the board somewhere. Oddly enough no short across the bridge rectifier. I'll find it eventually.

[tom66]

Re: Samsung PS50a410

Pulling out components 1 at a time but there is still a short on the board somewhere. Oddly enough no short across the bridge rectifier. I'll find it eventually.

If you can get hold of a computer power supply, you can smoke out the fault with 20 amps of 12V.

[nickdablack]

Re: Samsung PS50a410

Bah, kids sick. Haven't had time to get back to it. Hopefully will get a chance in a day or 2.

[nickdablack]

Re: Samsung PS50a410

Back finally. Let see:
Pulled out QS801 and QS802. Both of them have shorted across all pins. However there is still a short across pins 1-3 even with the components removed.
Bit worried if I try to smoke out the short I'll fry something thats currently fine. Is it really safe?

[tom66]

Re: Samsung PS50a410

Back finally. Let see:
Pulled out QS801 and QS802. Both of them have shorted across all pins. However there is still a short across pins 1-3 even with the components removed.
Bit worried if I try to smoke out the short I'll fry something thats currently fine. Is it really safe?

Can you post a pic under where pins 1 and 3 are?

[nickdablack]

Re: Samsung PS50a410

Here you go. It's doing my head in a bit. But I'll keep on trying. (as time permits)

[tom66]

Re: Samsung PS50a410

This short between 1 and 3 indicates a short between source and gate.

However looking closely at the arrangement it looks like Samsung use a small pulse transformer to drive the upper MOSFET - this is fairly common and will read as a short circuit. One thing to check is the small SMD diode near the gate - if there were a gate-drain short this poor little diode will have taken the brunt of it and is probably shorted - this might be why your new FET went bang as this diode is intended to prevent gate ringing (which wastes power in the FET... makes it get hot quickly.)

This pulse transformer is good news in a way because it limits the damaging surge which can go into the controller IC. So the IC may be okay.

Do you have a way of wiring in a 100W incandescent light bulb in series with your TV? This will stop the TV from blowing up more components if there's still a fault.

[nickdablack]

Re: Samsung PS50a410

One thing to check is the small SMD diode near the gate - if there were a gate-drain short this poor little diode will have taken the brunt of it and is probably shorted

DS804 is measuring .019v both ways. Yes i would say an ISS355 diode should not be measuring like that. However it doesnt look damaged and is paralel to a resistor. Iv'e taken an image up close.

[budm]

Re: Samsung PS50a410

I would suggest to take out the MOSFET, check and see if Gate to Source is shorted, since the resistor is in parallel with the Diode, then either take out the Diode or the resistor out and take the reading and see what is shorted out. It is always more accurate to check the parts out off the board.

[nickdablack]

Re: Samsung PS50a410

I got the tv going. I wish I could say I found the short and replaced the component. But I took the easy option and sourced a cheap replacement board. On the plus side I have a very happy wife so I am going to take that as a win. Now to move on to the other 2 dead plasma's in my garage.

Many thanks to all the advice everyone gave me. If anything it's brushed up my rusty electronics knowledge.