Worlds Best Socket 7 motherboard Repair , IC HOT

[Roli]

Hello , i have a FIC PA-2013 motherboard , i wanted to put in a new system, the board was working fine for 30 minutes , after that it started freezing and had to restart to make it work, and made a squeeking noise at the cpu capacitors ( the small SMD capacitors in the middle of the socket ) , suddenly the cpu fan stoped and turned on and did this a couple of times , after that the cpu fan socket ( 3 pin ) wasnt recieving 12V , so i had no more cpu fan spinning , after that the board just froze and died .
Now the motherboard wont post at all ...

So basically i identified a mostfet that is really hot, near the battery , its a 9435A -30V P-Channel Enhancement Mode MOSFET.
I uploaded 2 pictures where the hot mosfet is .

What i've done :

I replaced the 9435A also the 51031 ic and the diode
Recapped all main capacitors with new ones.
Checked for any short ( ive checked all small smd capacitors , none of them are in short )
Replaced 3 cpu-s
Tried with 2 power suplies
Tried with at least 10 memories
Cleaned the board
North bridge and South bridge look good because i cannot identify any short.
Checked the 2 VRM-S near the CPU , not in short .
Removed all main capacitors like 13 of them and started the board without them ( mosfet still getting hot )
And yes the jumper settings for the cpu are okay.
Checked for any dirt between ( Sdram slots , agp , pci )


Anybody can come up with some ideeas , because i have kinda ran out of them ��

Come lets ressurect this board , its the best motherboard in the world for the socket 7 platform, a holy grail ! , it would be a shame for it to die ��

[Dan81]

Re: Worlds Best Socket 7 motherboard Repair , IC HOT

Tried placing a SMD bead on CB62, as well as populating CT27?

[Roli]

Re: Worlds Best Socket 7 motherboard Repair , IC HOT

On CB62 there is a capacitor and its not in short , its okay , and CT27 there is nothing there by default construction of the motherboard .

[momaka]

Re: Worlds Best Socket 7 motherboard Repair , IC HOT

Well, you have a hot-running MOSFET, so I think that's a good hint where to start. In particular, measure the voltage on both sides of the round inductor L17 next to that MOSFET you indicated runs hot. Post what voltage you get here. It may also be a good idea to remove and check that diode connected to the coil - D3. Whatever you do, DO NOT power the motherboard without that diode or you will kill your RAM, CPU, or possibly even Northbridge. It's a single-ended buck regulator circuit, and those don't like to run without a free-wheeling device (in this case the diode.)

Removed all main capacitors like 13 of them and started the board without them

No offense, but that is a poor troubleshooting technique (and I'm only mentioning this so that people don't repeat it.) The capacitors are there for a reason - particularly on the buck-regulator circuits, like the CPU. If you remove them, you could kill your CPU. Granted these old CPUs are tough as nails. But try that on anything newer and it may not survive.

Anyways, do the voltage test mentioned above and post what you get. And check D3. When something is overheating, the best step is to see what part of the circuit that component belongs to, so then you may get an idea to hopefully narrow down where to troubleshoot. In this case, that MOSFET appears as part of the buck-regulator circuit for the Northbridge, given the proximity of L3 to the NB.