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've checked them all with a meter (in place) and one of them seems to be short circuited. I was considering desoldering it and then seeing if the board 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 here 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

In article ,
says...

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've checked them all with a meter (in place) and one of them seems to be short circuited. I was considering desoldering it and then seeing if the board 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 here 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

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

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

On Sunday, April 6, 2014 5:18:31 AM UTC+1, Phil Allison wrote:

** 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.


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...

** That is what overheated mosfets do.

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

** Worth a go, I'd say.

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

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

though.

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

On Saturday, April 5, 2014 11:36:11 PM UTC+1, Maynard A. Philbrook Jr. wrote:


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.

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?

On Saturday, April 5, 2014 12:34:12 PM UTC-7, wrote:
I have a faulty motherboard, it doesn't power up when the power switch is pressed. There are a number of faulty caps... I think it has taken out a MOSFET.

.... 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).

On 04/05/2014 12:34 PM, wrote:
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've checked them all with a meter (in place) and one of them seems to be short circuited. I was considering desoldering it and then seeing if the board 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 here 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


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

On 04/05/2014 12:34 PM, wrote:
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've checked them all with a meter (in place) and one of them seems to be short circuited. I was considering desoldering it and then seeing if the board 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 here 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

https://duckduckgo.com/?t=lm&q=P60N03LDG)

wrote:
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've checked them all with a meter (in place) and one of them seems to be short circuited. I was considering desoldering it and then seeing if the board 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 here 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

I don't have the patience for those horse**** 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.