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.
Check the DC voltages:Next, without any input signal, connect the voltmeter black probe to 0V (TP4 for EQ573) and note the DC voltages you get at the points shown on the picture below. Compare with the expected results (more or less 10%).
EQ573-II:
EQ573:
Try to follow the signalSend a good constant sine signal on input, like 100Hz - 2VAC measured between pins 2&3 of the input XLR.
All controls on OFF, source switch on XLR.
Connect the voltmeter black probe to TP4 and trace the signal on:
- TP1: 0.53VAC
- TP2: 0.46VAC
- TP3: 0.30 VAC
The reading should follow the input signal level.
The place where the signal drops will give you hints on where to look for.
