Replacing Voltage Regulator

[SOBEbev]

I have a motherboard with a fried voltage regulator. Specifically a power MOSFET transistor NEC 2SK3296. I admit ignorance with this type of work...I've never worked with integrated circuits. I want to try and get a replacement and try it out, but when I took all the specs on it to radio shack, I didn't know what to get and neither did they. They have 3 types of voltage regulators. A low voltage range one that I don't remember exactly, but if I was going to guess, I think I'd get this one. Then they had a 12v, and an adjustable, but I'm not sure how to adjust it. The voltage regulator says NEC K3296 14M. Would I risk damaging the processor or other components (I don't care about the motherboard) if I put on the wrong voltage regulator? I would think so, but I don't know anything about this...just thought I'd ask if anyone knew anything about it. Thanks for any advice. =)

David

 

[ScottMac]

Try DigiKey (www.digikey.com) or Mouser (www.mouser.com) and try a search on the NEC part number.

Rat Shack is no place to go if you need real hardware.

Good Luck

Scott

 

[Mark R]

You do not want a 'voltage regulator', and asking for one will yield confuse people and yield a whole string of inappropriate parts.

You need an exact replacement transistor. Unfortunately, switched mode regulators (like on your motherboard) are extremely fussy, and a similar part, may not work correctly - though if you get one with a better specification you will be very unlucky to have it not work.

Basically, you need a Logic level N-Channel Power MOSFET in a D2PAK package rated for at least 35A. Something like a IRF3704S should be satisfactory and readily available - Digikey should have one.

Good luck soldering. Surface mount is tough, and I've no idea how to get the old one off without destroying the board. My normal technique of using a blowtorch probably wouldn't be ideal.

 

[sciencewhiz]

warranty service?

 

[lenjack]

digikey is always the place to look. You can get their catalog online or ask for one at no charge.:beer:

 

[KalTorak]

This is doable, but it's tough.

Mark's right - replacing a transistor in a switching VR does require kinda careful part selection in order to get the exact same behavior as you had before. But I'm of the school of thought that says a couple mOhms difference in Rds_on or a few percent difference in gate capacitance isn't going to make a difference that you'll be able to notice.

Further, there's a chance that this transistor was the pass element in a linear VR, in which case damned near any FET of the same type (N-channel vs P-channel, enhancement vs depletion) will work. Was your dead part kinda near other FETs like it and near inductors and capacitors, or off amidst smaller components?

Anyway, to remove such a part (I just pulled a D2PAK off a board last week), ya really need a heat gun - it's kinda like a blowdryer, but hotter and more focused. It's gonna be really difficult to adequately heat the thing with a soldering iron, because the board's designed expressly to remove heat from that transistor (since it's gonna get hot in normal operation as part of the VR, it makes sense to design the board to act as a heatsink for the transistor, which is bad news if you're TRYING to heat it.)

Anyway, look up what Rds_on at various Vgs voltages is for your NEC transistor, and try to find a replacement with the same or lower Rds_on at those voltages. If ya can manage, try to find one with a gate capacitance no larger than the one you're replacing. Good luck!

 

[SOBEbev]

Thanks for all the great advice. The transistor had already loosened itself and came off without a fight. I already ordered another motherboard for 25 dollars so I could get my friend back up and running. I still want to attempt to revive the board for fun. I think I'll check out digikey or possibly just try to find someone who might have a dead motherboard with one of these on there. Yes the transistor was in a line of other transistors and surrounded by capacitors. Thanks again for all your expertise!

David