Fender SPL 9000 , 1997 slave amp
 

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.

Fender SPL 9000 , 1997 slave amp
 

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

Fender SPL 9000 , 1997 slave amp
 

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