I have a new/old ASRock K7VT6 motherboard that I have never used. It will not start the power supply by shorting out the start pins, no action at all. I have tried several different power supplies from 300 to 550 watts, no ram, no video card and the PS's work on other boards. Obviously there is no initial power to the start pin, what voltage should the pin show, second pin is ground. I have inspected the board on both front and back and no bad solder joints.
Because it is a brand new board I feel it was never shorted or burned? If I had a diagram, maybe I could find the problem.
Repairing MBs is a chore even with proper equipment. I believe all you're doing when you short the two pins is to ground a logic pin so I wouldn't be surprised if there was no voltage on it. Are you sure you are connecting the proper pins? Could the silkscreen be wrong? Are there any LEDs on the board to indicate the PSU is supplying power? Is there a power switch on the PSU?
I've been doing this for 35 years on thousands of systems. First time I've ever seen a new MB that there is no activity when shorting the pins on the MB with several diff. PSU's. I can't find a wiring diagram to determine the path or voltage of the "start" pins on the MB.