| Author | Message | ||
| Mike Griffin (mgriffin155) Username: mgriffin155 Registered: 02-2014 |
I have a 1981 MM112-RD-65. Lately I hear a loud pop when switching from Standby to Lo or Hi. It's usually louder when switching to Lo. Could the Standby Switch be going bad? | ||
| Mike Kaus (mm210) Username: mm210 Registered: 05-2006 |
Yup. Very possible. | ||
| Mike Griffin (mgriffin155) Username: mgriffin155 Registered: 02-2014 |
Hi Mike, Thanks for the quick response. Have you ever had this problem on an MM Amp you've worked on? I saw one of Ed Goforth's posts that mentioned a similar pop with the Standby/Off/On switch on a RD-50. He had an interesting fix but I'd rather not have 700+ volts on a panel switch. Here's a little history: A couple of months ago, I started bringing this amp back to life. It had spent several years in a state of neglect inside a friends leaky storage shed. I convinced him to let me give it a new home. When I first powered it up, the lights came on but no one was home. I quickly determined the MM speaker was fried. Scratchy voice coil and infinite ohms. After I replaced the speaker (Celestion Creamback), I found the reverb circuit not working. The tank and driver IC were replaced and the reverb started working but the amp didn't sound so good. About that time I found this site and proceeded with changing all the electrolytics and cleaning all the pots and jacks. Mouser is a great source for parts. Thanks. Next issue was a loud pop (similar to the Standby Switch pop) when engaging the Distortion channel. That was caused by a loose .1uF cap in the Channel selector CMOS switch driver circuit (bad solder joint to ground). Most likely I caused the cap to come loose when I was replacing the electrlytics and some resistors. Whoops. There are 2 .1uF caps close to the dirty channel dual gain pot that get pushed a bit when the PCBoard is lifted. So when the Standby Switch started giving the pop, I assumed there was some other cap or part I'd accidentally knocked loose. Further inspection of the PCB didn't reveal any loose parts so I figured it was time to get advice from folks with more experience. Back to the STBY switch: Funny thing is sometimes there is no pop when switched to Hi or Lo. It also seems to behave better when I slowly toggle it while pulling on the baton. I'll order a new switch and hope for the best. I'll report back after I change it out. Live and learn. Now if I could learn to play guitar........ Thanks, -Mike |
Tue, 03/25/2014 - 09:55
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