D) Unit Powers Up, But Does Not Unmute (Pass Signal) - Meyer Sound MP-4 Service Manual

D. Unit powers up but does not unmute (pass signal):
1. If the amplifier is in the speaker cabinet, remove the eight (8) large head screws that attach
the amplifier to the cabinet. As you slowly remove the amplifier from the cabinet, look at the
green speaker connector(s) on the top of the amp chassis. Make sure that the connector(s)
is fully seated. If it is not fully seated, seat the connector and push the amplifier back in the
cabinet. Apply power and signal. If the unit still does not pass signal, unplug the unit and
remove it from the cabinet.
2. Make sure to check the drivers in the cabinet for shorts or opens. Refer to Low Driver
Inspection and Evaluation Procedure for Self Powered Series Products (# 17.010.120.01) and
to High Driver Inspection and Evaluation Procedure for Self Powered Series Products (#
17.010.120.02) If the drivers are fine proceed to troubleshoot the amplifier.
Note: High drivers will have a capacitor in series making resistance measurements inaccurate. High
drivers can best be reached by removing the closest handlecup on the cabinet.
3. With the amplifier sitting on a firm surface, remove the eight (8) small head screws from
the user panel.
4. While slowly removing the user panel, disconnect the audio signal cable from the input
board on the user panel by disengaging the gray connector. Also disconnect the AC input
connector (4 wire green connector) on the AC mains board.
5. Check the sense cable (gray ribbon on AC mains board) connection. Make sure that it is
connected properly.
6. Replace the user panel and attach a load to the amplifier. If you are using a resistor as a
load, attach a voltmeter to the output as means to monitor the output. If you are using the
cabinet, simply connect the speakers. Apply power to the unit and input a signal.
7. If the unit still does not un-mute, the muting relay circuit on the control board or the
muting control circuit on the Power Supply module could be damaged.
8. Replace the control board with a known good board (make sure that it is the same type).
Refer to Meyer Sound Self Powered Series TruPower Limiting Upgrade Procedure (#
17.033.042.01 for MP-2 and # 17.033.042.02 for MP-4 ). If the unit still does not un-mute, the
Power Supply module is probably damaged. As Power Supply module failures are rare, it
is recommended that you return the unit to the nearest authorized service center for further
evaluation.
Self-Powered Concert Series
Service Manual
MP-2/4 Amplifier
© 1998 Meyer Sound Laboratories, Inc. All rights reserved.
Doc #: 05.033.040.01
Rev.: A
Date: 08/31/98
Page: 21 of 26