[JPK]

Check the usual suspects:

• Forgotten solder joint,
• Bad solder joint (reflow suspicious joints),
• Reversed components (electrolytics, diodes, transistors, IC's). In case of IC's, probably destroyed, better replace,
• Flipped IC's or transistors,
• Trim all the component leads and test pins as short as possible. Nothing must touch the chassis plate.

Try to follow the signal
Send a good constant sine signal on input, like 100Hz - 1VAC measured between pins 2&3 of the input XLR.
All controls on OFF, EQ is IN.
Connect the voltmeter black probe to the 0V pin and trace the signal on (values +/-10%):
TP1: 0.57VAC
TP2: 0.54VAC  /  89VDC
TP3: 0.53VAC
TP4: 0.5VAC  /  89VDC
TP5: 0.5VAC
TP6: 0.5VAC