About half the solder joints on the input sub-board are bad. A .25 and M&F XLR each ch with no obvious reason why, as all sockets are individually fixed to stout chassis metal . Even the never been used quarter inch sockets have bad solder joints. The solder looks good otherwise.
Probably the sockets were soldered onto the pcb without laying on a jig. So misaligned when fixed onto chassis. So inbuilt stress in board combined with the board being in the internal hot air flow to the fan
unbalanced "reference planes". insulated 1/4 in i/p sockets . Lipped insulator washer and star washer inside chassis but only the insulator washer packing lines up with XLR rear faces, just that 1/10 inch or less enough to stress the board/solder
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