You will need to remove either the top or bottom panel to get at the jacks. There is probably a bad solder joint that needs to be repaired. You might try tightening the screws on the XLR jacks that fasten them to the back panel first and the nuts that fasten the 1/4"jacks also. I really do not recommend you do this yourself ( accessing the interior) unless you have electronic servicing experience as the filter capacitors in the power supply store a dangerous charge and are soldered to the circuit board in fairly close vicinity to the output stage.
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You will need to remove either the top or bottom panel to get at the jacks. There is probably a bad solder joint that needs to be repaired. You might try tightening the screws on the XLR jacks that fasten them to the back panel first and the nuts that fasten the 1/4"jacks also. I really do not recommend you do this yourself ( accessing the interior) unless you have electronic servicing experience as the filter capacitors in the power supply store a dangerous charge and are soldered to the circuit board in fairly close vicinity to the output stage.