Hp Vs17

[Oklahoma Wolf]

Ok, I've about had enough of this one. The patient, an HP VS17 (PK657AA), was given to me by a friend and is determined to send me to the crazy house.

Initial symptoms were the thing would turn on for a couple minutes and then go dead like the power was cut. Power button would not turn it back on. I went through it and touched up every bad solder joint I found, and replaced several capacitors.

That got it to run for a couple hours instead of a couple minutes, but it would always go dead again. Pointing a fan at it made it stay on indefinitely, but then if you tried to turn it off with the button it would play dead again. It would not power up again unless you cut the power to it for a while.

Replaced the 47uF 50V capacitor near the FAN7601 PWM controller. That got the power button to work properly, so I figure I'm getting closer. Measured the voltage at the Vcc pin on the PWM... 61 volts. Seems a bit high - the chip is rated for 20V. That's gotta be part of the problem.

But, I'm now at a dead end - not sure what's causing the Vcc pin to get that much voltage. I have a part on a heatsink I can't ID - picture attached (it's the MOSFET dead center in the pic). 5V output reads 6.31V, 12V output is at 12.01V. 12V happens at the regulator at the very top of the board, next to the 5V and 25V output heatsink. 25V output reads just under 25V.

Anyone have any thoughts on where next to look? Any help is appreciated.