Appreciate the suggestion. I reinstalled the A3 and tried cycling all the PSU connectors, including the motherboard one. I also brushed a tiny dab of Deoxit D100 on each male pin and cycled the connectors a few times.
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Unfortunately, no changes.?
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I also checked all of the power supply test points that are made accessible. All of the voltages seemed present and at a reasonable level:
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One thing I observed on the back of the A3 board are the presence of red LED. These seem to be connected to different power rails on the back of the board.
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I noticed that 1 LED was very dim and the other was not lit. These are visible with the outer cover off, through the chassis air holes where the A3 is slotted.
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The 2 LEDs in question are the bottom most ones, which are connected to the 2 TO-220 voltage regulators U18 and U19.
Not sure what the "normal" condition should be; are both normally lit when no issues are present?
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U19 is an ON semi CS5208-1. Datasheet is as follows:
Compare to U18 which is an LT1085:
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The CS5208-1 is not available anymore, but the LT1085/1084 are. As far as I can tell, these are nearly identical regulators?
The CS5208 is rated to higher currents (6V, 9A) while the LT1085/4 is tolerant of higher voltages (30V, 3/5A). However, the pinout and output divider adjustment equations are identical?
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I can get the LT1084 on Digikey. Maybe its worth swapping both U18 and U19 out with new LT1084 and seeing if anything changes?
Kevin A.