This sounds like a problem I had in an instrumentation recorder years
ago. Turned out to be a manufacturing quality control slip up. The
fault took up to an hour to appear. Finally, while troubleshooting some
other circuit in the area of what turned out to be the fault cause, I
saw the fault appear just because we were mechanically working near it.
It was a heat induced fault on an unsoldered wire to lug connection.
(A poorly soldered connection could do the same.) Heating made the
connection move apart from the lug and go open circuit.
Use a high power light and magnifier to examine all the soldered
connections. Touch up any that look less than pristine shiny joints
with good wetting.
You might try to induce the fault by putting pressure sidewise on
connections near the suspect solder joint. Since it evidences itself as
low power, look first at all the power busses and regulators. Since you
have symptoms on the receive side, go back and start tracing from the DC
power supplies.
GL!
Stuart Rohre
K5KVH
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