Possibly shorted FETS GA-MA770T-ES3

[lbwlow]

Hi all, I got a Gigabyte GA-MA770T-ES3 AM3 board that I suspect has 2 shorted FETS as it become super hot to touch as soon as the PSU is switched on. I was unable to switch on the board, I am guessing the board has detected a short and don't allow me to turn on. But I was able to measure voltage on both of the suspected shorted MOSFETS:
1) Highlighted in red, I was getting 4.9V (K3918)
2) Highlighted in yellow, I was getting 0.4V (Nikos L1085DG)

There was a Nichicon HM(M) 6.3V 1000uf next to the MOSFETS, highlighted in orange. When I was doing troubleshooting, I got no resistant on the leads of the caps, therefore I suspected it was the caps that had gone shorted, then I removed the caps for further testing. The cap was totally gone, although when testing out of circuit, there was resistant, but when I test it again using capacitance function, I am getting OL. After removing the cap, the MOSFETS still heatup as before.

What your opinion guys ? Should I replace those MOSFETS ?
Thanks in advance

[lbwlow]

Re: Possibly shorted FETS GA-MA770T-ES3

Alright I figured out what wrong with the board, therefore prob is fixed.

The LAN chip been shorted before the board was passed to me, as always I will touch the LAN chip whenever I sees a board that don't turn on / POST, this is because in my country there are still many people using phone line DSL internet, and always thunderstorm would fry the LAN chip. I did touch the LAN chip, but it is just a very very faint warm, therefore I tought it was normal. Until I replace the suspected shorted Nikos FETs with another Nikos N channel FETs. Now when connect the board to the PSU, now the LAN chip heat up real fast, I can't touch it for more than 1 sec. Immediately shut off the PSU and disolder the shorted LAN chip.

So the conclusion was, the shorted LAN chip took the Nikos FETs and the Nichicon cap with it. Now I am able to turn on the board and passed memtest.

[momaka]

Re: Possibly shorted FETS GA-MA770T-ES3

Good save!
Would not have thought the LAN chip could burn those rather large MOSFETs. I guess we learn something new every day. Thanks for your post.

[lti]

Re: Possibly shorted FETS GA-MA770T-ES3

The L1085DG is actually a voltage regulator.



Where did you measure voltage?

[momaka]

Re: Possibly shorted FETS GA-MA770T-ES3

The L1085DG is actually a voltage regulator.

You're right!
Anything with 1085 or 1086 in the part number is more than likely a voltage regulator.