Replacing burnt MOSFET

[Fatfool]

Hi Guys,

Really need someone to point me in the direction here. So I've got this PSU board with a burnt MOSFET which is presumably stopping it from working. How do I replace this MOSFET? Preferably an uprated MOSFET as this same MOSFET has already burnt out once.

I can usually DIY things myself and am an Engineer.... just not an electrical one. Hence, I don't know how to do this nor do I understand the principles behind MOSFETs

 

[Morugana]

google for surface mount soldering.

another thing is the burnt surface might affect the original wiring on the PCB board.
there should be some kind of pin hole for you to check the connection on the board using a multi-meter.

MOSFET is just an ic chip. follow the specs align the feets.

TLDR: what kind of PSU? with so much hassle. why not just buy a new one

 

[bunnypangsai]

idk where you can get the chip. But if you find it, use a heat gun with small mouthpiece. Alternatively you can use a soldering iron.

 

[wwenze]

http://sg.element14.com/on-semiconductor/ntd25p03lt4g/p-channel-mosfet-30v-25a-d-pak/dp/1736465

You can replace it with the same one. The one you have is likely fake if the board is from China. The part is rated for 25A so burning out in a board like this that doesn't have any cooling is just bullshyt.

 

[Fatfool]

google for surface mount soldering.

another thing is the burnt surface might affect the original wiring on the PCB board.
there should be some kind of pin hole for you to check the connection on the board using a multi-meter.

MOSFET is just an ic chip. follow the specs align the feets.

TLDR: what kind of PSU? with so much hassle. why not just buy a new one

This is a custom size board like PSU. 150W with no housing. Hmm I don't have a multimeter too. This PCB doesn't look like a breadboard.... what does the pinhole look like?

 

[Fatfool]

http://sg.element14.com/on-semiconductor/ntd25p03lt4g/p-channel-mosfet-30v-25a-d-pak/dp/1736465

You can replace it with the same one. The one you have is likely fake if the board is from China. The part is rated for 25A so burning out in a board like this that doesn't have any cooling is just bullshyt.

Hmm the board came as part of a case. I think the adapter that plugs into it might have caused a short (adapter tip is broken)

Um... not confident of replacing myself. anywhere to go to get it fixed or tested?

 

[||||||||||]

I tried to desolder surface mount components before, it's a bitch to remove with one solder gun.

Only manage to remove using 2 solder to melt both sides

 

[commach]

What's the value of the capacitor on the upper left corner?

Using a capacitor way higher than what's is required can lead to premature failure. If you DIY to replace this failed P channel mosfet, be sure you solder it as much contact to the board as possible, else you risk premature failure due to poor heat dissipation.

 

[yau_chee]

Maybe next time add a small heatsink on it.

 

[bunnypangsai]

What's the value of the capacitor on the upper left corner?

Using a capacitor way higher than what's is required can lead to premature failure. If you DIY to replace this failed P channel mosfet, be sure you solder it as much contact to the board as possible, else you risk premature failure due to poor heat dissipation.

spam flux ah!

 

[Fatfool]

What's the value of the capacitor on the upper left corner?

Using a capacitor way higher than what's is required can lead to premature failure. If you DIY to replace this failed P channel mosfet, be sure you solder it as much contact to the board as possible, else you risk premature failure due to poor heat dissipation.

It's 470 μF wah I'm blur already! what in the world is a P channel MOSFET!!! Is it possible that a short ended up burning that MOSFET? cos I have 2 boards with this MOSFET burnt.

 

[Fatfool]

Maybe next time add a small heatsink on it.

Don't think it's overheating? perhaps a short? cos they didn't burn after running for a long time. They burnt soon after turning the machine on. I have run one of them for a period of time without incident but the next time I plugged the adapter into it and turned it on, there was smoke.

 

[commach]

It's 470 μF wah I'm blur already! what in the world is a P channel MOSFET!!! Is it possible that a short ended up burning that MOSFET? cos I have 2 boards with this MOSFET burnt.

I'm not entirely sure what's the best fit capacitance for your power supply board due to lack of actually power requirement.

I've seen a couple of time the filter capacitors are too "big" for the circuit which result in a abnormally high inrush current.

It will be TL;DW to explain it, please read this explanation for why the filter capacitor is too big in same cases.

I'm currently working (took over) on a prototype previous designed by a so called "master class" electronic expert. It is a pair of circuit board designed to drive 2 unit of 1ampere stepper motor on Arduino platform, driven by a pair of Pololu A4899 1/16 stepstick. He set the vref to 0.5v which in paper, match the stepper motors flawlessly. But the tester/trial user complained about abnormally low torque and irritating humming noises. Unable to find a solution, this joker simply abandon the project and never come back to fix the problem.

I suay suay took over this sh!t and start troubleshooting, didn't take long to find out the actual problem. Vref 0.5v is way too low because the pair of stepper motor are running in fullstep mode. Pololu A4988 output under full step mode is 71% which meant at vref 0.5 (no heat sink required), the actual output is only 0.355v and not 0.5v, adjust the pot to 0.7v solved the problem once and for all.

 

[commach]

In general, mosfet are either P or N channel (there are exception), those mosfet on the computer motherboard are usually N channel mosfet and those on PSU's board are usually P channel.

 

[lalalalalala]

P mos and n mos operate on different principles, I.e how the gates/current pass thru it.

Anyway your board is just badly designed or the capacitor is not doing its job.

This type of surface mount is the hardest to solder

Sent from OnePlus A0001 using GAGT

 

[quekky]

I tried to desolder surface mount components before, it's a bitch to remove with one solder gun.

Only manage to remove using 2 solder to melt both sides

u need solder sucker

 

[bunnypangsai]

u need solder sucker

or wick. prefer wick tho.

 

[devilwahaha]

Since its already dead cant you just snip off the two small legs and desolder the fat pad instead

 

[wwenze]

Don't think it's overheating? perhaps a short? cos they didn't burn after running for a long time. They burnt soon after turning the machine on. I have run one of them for a period of time without incident but the next time I plugged the adapter into it and turned it on, there was smoke.

Then it can be the adapter. You haven't mentioned what adapter it is.

I don't see any form of output protection for that mosfet so a short on the load can kill that mosfet easily. Though I wonder why the external power supply doesn't go into overcurrent protection first.

 

[Fatfool]

I'm not entirely sure what's the best fit capacitance for your power supply board due to lack of actually power requirement.

I've seen a couple of time the filter capacitors are too "big" for the circuit which result in a abnormally high inrush current.

It will be TL;DW to explain it, please read this explanation for why the filter capacitor is too big in same cases.

I'm currently working (took over) on a prototype previous designed by a so called "master class" electronic expert. It is a pair of circuit board designed to drive 2 unit of 1ampere stepper motor on Arduino platform, driven by a pair of Pololu A4899 1/16 stepstick. He set the vref to 0.5v which in paper, match the stepper motors flawlessly. But the tester/trial user complained about abnormally low torque and irritating humming noises. Unable to find a solution, this joker simply abandon the project and never come back to fix the problem.

I suay suay took over this sh!t and start troubleshooting, didn't take long to find out the actual problem. Vref 0.5v is way too low because the pair of stepper motor are running in fullstep mode. Pololu A4988 output under full step mode is 71% which meant at vref 0.5 (no heat sink required), the actual output is only 0.355v and not 0.5v, adjust the pot to 0.7v solved the problem once and for all.

hmm so you reckon sticking to the same rating is better? Otherwise it stores way more energy than needed (and can't release till a few cycles?) I had a brief run through it and I see that a cap is meant to store energy from a rippling AC (oxymoronic to make that statement I know)

So, anywhere to find a less than master class electronics expert to figure out what capacitance is needed and to solder a MOSFET on?