On Tue, 2 Jan 2018 00:49:06 -0500, Bill wrote:

Before I found my "fix" I was producing
"spurious results" by pressing down at various placed on the MB. You
might try that after you check out your power supply. Good luck!

Yeppers. Variously "fixing" a few tubed amps with that method.
Breadboard the chassis and use a rubber tube (ink eraser) for
carefully pressure-testing audio dropouts. Hit-&-miss, or less than
ideal factoring for "re-flowing" solder joints. Amps and Fx pedal
boards, although usual and common fixes, being for not much other
choice;...Least to mention cheap, being on my time.

I've noted others use refrigeration (spray cans) for quick freezing
areas with suspect "cold" solder joints in a similar fashion.

Ribbons and PC data cables are another frequent area now for cutting
amp costs, additions to a list of amp features that may oxidize into
turning up suspect. Some pull them and redo the connections as a
point-to-point safeguard.

With a computer there's no re-flowing, and QC issues involving
physical continuity at a core componentry level becomes altogether
unacceptable.