[JPK]

1. 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.

2. Check the DC voltages:
First check the supply voltages as described in the setup guide.
Check you get no DC volts on TP1. Any DC above a few millivolts here shows that there is an issue.

3. Try to follow the signal

Send a good constant sine signal on input, like 1VAC measured between pins 2&3 of the input XLR. PEAK at 0.
Connect the voltmeter black probe to 0V and trace the signal on:
- R2 right pin: Should be at 0.7VACand follow the input voltage.
- REV1.3: R5 low pin should be at 0.5V when GAIN is on 100.
- REV1.4: R5 right pin should be at 0.5V.
- TP1: should go above 10V when GAIN is at 100.

Check the input transformer coils resistance

1    3    5
o  .  o  .  o

              BOTTOM VIEW

o  .  .  o  o
10      7  6

1-5  ? 2 kohms
6-10  ? 2 kohms

Check the output transformer coils resistance

1    3  5  5  6    8
o  .  o  o  o  o  .  o  PRIMARY

      BOTTOM VIEW

o  o  .  o  o  .  o  o  SECONDARY
16 15    13 12    10 9

1-3  ? 10 ohms (5 ohms if in circuit)
6-8  ? 10 ohms (5 ohms if in circuit)
9-12 ? 12 ohms
13-16 ? 12 ohms