Finding a replacement MOSFET

I have a faulty motherboard, it doesn't power up when the power switch is p ressed. There are a number of faulty caps that I'm in the process of replac ing but the only time I successfully powered the board on there was a audib le 'crack'. I thought this was a cap venting but I think it has taken out a MOSFET.

I've checked them all with a meter (in place) and one of them seems to be s hort circuited. I was considering desoldering it and then seeing if the boa rd powers up (even partially). If that's successful I was going to try and track down a new MOSFET. I don't seem to be able to find the exact part her e in the UK (NIKO P60N03LDG) but I've found the datasheet. What properties do I need to match to get a substitute?

Am I likely to be able to get the board working again or should I just junk it?

Thanks,

Simon

Reply to
simonrowe60
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Junk it. Because if you smoked that part, there is a good reason for it.

maybe you put a cap in backwards.. Any way, if do plan on replacing the MOSFET, it's a logic level type which means the gate voltage Vgs(thr) is low. Also it's a

60 Amp continuous part with 12 mohms. So you need that or less.

Jamie

Reply to
Maynard A. Philbrook Jr.

I have a faulty motherboard, it doesn't power up when the power switch is pressed. There are a number of faulty caps that I'm in the process of replacing but the only time I successfully powered the board on there was a audible 'crack'. I thought this was a cap venting but I think it has taken out a MOSFET.

** I found then when some 1200uF 6V electros when bad on the MOBO in my previous PC, a mosfet associated with one of them got VERY hot. New electros fixed that completely.

I've checked them all with a meter (in place) and one of them seems to be short circuited.

** That is what overheated mosfets do.

Am I likely to be able to get the board working again or should I just junk it?

** Worth a go, I'd say.

Fitting the new SMD mosfet to the PCB is gonna take some skill and care though.

Changing electros is tricky enough.

.... Phil

Reply to
Phil Allison

These were 1000uF 6.3v caps. I was hoping the board was salvageable, I'd just fired it up to check that I had a working baseline when it went pop...

Is this short likely to have caused other parts to fail?

Is removing the dead MOSFET and trying to power up the board a safe thing to do?

Yeah, I've only got a 40W iron, the caps came out reasonably easily using a heat gun to pre-warm the board. I was hoping to do the same with the MOSFET.

Simon

Reply to
simonrowe60

I've a couple of scrap boards, one has P0903BDG and P75N02LDG MOSFETs. I'm assuming the P090's are no good as they're rated at 50A. The P75's have a higher Vgs(th): 1/1.5/3V. Does that rule them out too?

Reply to
simonrowe60

... one of them seems to be short circuited.

When the MOSFET is replaced, you'll know whether the drive circuit to that MOSFET was also burned up; usually there's a gate resistor (maybe 10 ohms) and an IC with a high-current driver transistor, either or both of those can go out when a MOSFET blows. If it's on a motherboard, the drive circuit is likely to have survived (has low voltage input), but in an AC supply, such drivers will often see high DC voltages in a short, and fry. Trace the gate from that MOSFET, and look for a resistor (with a microscope, probably).

Reply to
whit3rd

If it's just being used as a switch it should be easy to substitute. MOSFETS take out their neighbors when they fault shorted.

Reply to
dave

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Reply to
dave

I don't have the patience for those horseshit 900 clicks and a popup datasheet sites, but if you can use a couple 13n03 mosfets from a dell systemboard I can cut some out of a board and mail them from the US.

Reply to
Cydrome Leader

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