Quad Preamp volume drop on Ch 2

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killertaco

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Just spent $150 with a "Mesa certified repair guy" only to have him clean the face and replace a few screws after having it for 3 weeks. Didn't help the problem at all. So, do you think I just need to replace the first "volume" pot on Ch 2? I have read a lot about the LDRs being bad and not sure what the symptoms of that are. Any input would be much appreciated.
https://www.youtube.com/watch?v=cE4I3b9Jd4s
 
Pretty sure my service guy cleaned them all. One thing I didn't show or mention is that it changed if you take bass and mid from 0 to 10 as well. Doesn't get rid of it but changes drastically. I have a pot coming and hope that does the trick. Thanks!
 
Back to the repair guy and thinks it is a coupling capacitor this time.....Hopefully back in action next week!!
 
If I gave someone $150 for nothing in return, there would be a problem regardless if the amp functioned or not!

I had a tech go through mine a while back and give it a complete cleaning after it started becoming inconsistent and weak sounding. I was afraid I was going to have to replace the ARMADA or tubes, but it just needed a bath! :mrgreen:
 
Its a bad LDR. It is a VERY common problem on these units. I had the LDRs changed out in mine by Mesa once when the unit was about 10 years old. About 10 years later had the exact same problem you are having with channel 2. I changed the LDR for that circuit which fixed the problem. I sold the Quad shortly thereafter. I didn't want to risk having to replace LDRs every 10 years. They are obsolete technology and are not getting any easier to source with time.

Have your tech look at the schematic for the Quad. He'll be able to identify the bad LDR. I'm surprised a "Mesa certified" tech didn't pick this first thing. It is the most common failure mode on these old units.

You could send it back to Mesa and they will fix it like new -probably cost about $300 or so. Its fiddly work.
 
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