| Author | Message | ||
     Brian W. Beebe |
Greetings, I am a newcomer to the board and the proud owner of my first Music Man amp, a 112 65 made in 1979. The amp is in nice shape but doesn't make any sound. The tubes are new and working and the speaker is hooked up. Is there any other obvious thing I can troubleshoot? Thanks, Brian | ||
| Steve Kennedy (admin) Username: admin Registered: 03-2002 |
No sound could be caused by a number of things: 1. Standby switch is in the Standby position or has failed and is stuck there. 2. High Voltage plate DC supply has failed (not shorted). 3. Speaker cable is shorted or open. 4. Speaker voice coil is shorted or open. 5. Speaker cable is plugged into wrong jack (along with a defective jack switch). 6. Shorted or open output transformer. 7. Failed/missing/incorrect 12AX7 Phase-splitter (if used) 8. Open/missing/incorrect output tubes. Does the amp make ANY noise with all the gain controls full up (don't give it any input signal). If it is dead quiet, then the points above describe the most likely scenarios. If you can get hiss or hum but no output when a guitar is plugged in, then a preamp component failure or a power supply failure is likely. Since the speaker is an external component, check it's operation with a battery or ohmmeter and check the speaker cable as well. To get any deeper will require actual circuit troubleshooting. Make sure that the power supplies are checked first. If all the power supplies are working then verify the input and output jacks are working, clean (not corroded) and not shorted. Verify that the jack switches are working properly (switching contacts on the jacks that short, open or switch the signal when a jack is plugged in). Steve | ||
| Brian W. Beebe |
Thanks for the reply Steve. The amp is dead quiet when turned up, so I sent it to my amp tech as it's probably beyond my capability. I hope it's something simple, and inexpensive to fix. Thanks, Brian | ||
| Brian W. Beebe |
Steve, I found out today that the only problem with my amp was a 50 cent resistor in the pre-amp section. I was advised by my amp tech to do an upgrade to the op amp and replace filter caps but Skipp Isaham advised against it. Thanks for your help. Brian | ||
| Steve Kennedy (admin) Username: admin Registered: 03-2002 |
I'm glad you got it sorted out with only a resistor replacement! Sometimes you get lucky. It could have been an output transformer! Thanks for the post-mortem report. Steve | ||
| Brian W. Beebe |
Steve, Post script: My amp tech had to replace the aux. AC socket on the rear of the chassis. He used a newer, square receptacle requiring him to make the original opening larger; OUCH. I would have preferred if he had left it original but it's too late now. For future reference, are there NOS or OEM sockets as well as other MM parts available? Thanks, Brian |