The first thing I recommend that you do is to look at all the PSU cables in the PSU area including the big multiwire one that loops back to the motherboard.
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As a first attempt, try partially removing each connector from its header and walk it up and down a few times on its header pins to try and remove any oxidation. Do this for all the connectors in this area including the big multi-way connector that loops back the CPU area. I think this one has lots of brown wires. Wiggle and walk them all in their pins and retry the unit. It could be that you have excess voltage drop in the connections to the A3DSP board.
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