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If you tap the the bottom side of the board in CPU section at times the fan will spin and boot properly according to bench power supply but only for a few seconds to a couple minutes then turns off again.
Does this sound like a internal problem with the new behavior?
During testing noticed L7560 voltage was fluctuating. A couple times the fan even spun during the test. Replaced Q7560 but no change. Should U7501 be replaced?
Check for pulse at pins 7 & 3 of U1950.
Inspect all SPI Bus Termination resistors and their traces.
PLT_RESET_L pulses too?
Any pulse detected at CPU coils?