[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.
• Make sure that resistors R1, R3 do not touch the transformer daughterboard pins.
• Make sure that capacitor C12 do not touch the transformer daughterboard pins. It is very close and if the pins can pierce the insulation the circuit will oscillate.

Voltages checks: +/-20%

Initial conditions:
IN pot @ max
OUT pot @ min
REC pot @ max
Bypass toggle @IN
All Push buttons @UP
Input signal: Sinus 1kHz, 1VAC
Jumper JMP1: removed

Results:
TP1 = TP2 = 30VDC (black probe on 0V)
TP1 = TP2 = 1.25VAC
TP3 = TP4 = 1.8VAC
Output: 3.5VAC (between XLR pins 2&3)

Changed conditions:
Jumper JMP1: on 1-2
Input signal: Sinus 1kHz, 0.3VAC
OUT pot @ max

Results:
TP3: 0.26VAC (black probe on 0V)
TP4: 3.1VAC
TP5: 2.9VAC
TP6: -3.5VDC
Output: 6.1VAC (between XLR pins 2&3)
Meter: -6dB

In case you need to remove the input transformer follow these steps

• Remove the 4 screws on the transformer (2 in front and 2 in the back).
• Remove solder on the 7 pads connecting the front daughter board to the main PCB. Use a desoldering pump.
• Pull the transformer and front daughter board together.
• Remove solder on the 9 pads connecting the transformer in/outs to the front daughter board and remove it.  Be careful when removing the front daughter board not to pull the transformer front plate with it because it is not attached anymore.