Cheers mate that explains why I couldn't find it. You mis-typed PQ49 not PQ59
That isn't good is it, for anything that was on the 1.2V rail. A drain-source short on PQ59 is going to connect Vin directly to the 1.2V rail so 19V is likely to go to where it shouldn't. Until of course the PSU trips out or whatever.
This is also a good example why you shouldn't power the 19V with your bench supply to see what gets hot on the lower voltage rails. You should power the short circuit rail directly with the inductor removed and your bench supply set for the maximum voltage of that rail. Which was my original posts suggestion. Having said that you already had a low resistance on this rail before you started powering with the bench supply so any damage done was already done.
So even before you change the s/c FET PQ59 you need to find out why you have a 5.1 ohm low resistance on the load side of PL12 other wise you will quite likely just blow the replacement FET anyway. If you still have 5.1ohm on PL12 that is. I assume you still do?
I would connect a lab supply to the load side of PL12 set to 1.2V maximum and with current limit on. Then wind up the current and see what gets hot - but from various observations so far it is going to be the GPU. The schematic says this 1.2V 7A rail is the VGA supply.
Alternatively you could try my trick of warming and cooling the GPU and at the same time measure resistance PL12 load side to ground. If you have a sensitive DMM and can read 0.01ohm or 0.1ohm increments and the resistance changes when you warm the GPU that is another good indicator you have located the underlying problem.
What part number is the GPU anyway? Is it a BGA package, or something more easily workable?
Rich