Mesa Mark IV lead mode drop out during warmup

[edge59]

HI there, I have a Mesa Mark IV that I have been trying to trouble shoot. When in the lead mode, every so often the gain fluctuates (looses gain and comes back) as you turn the knobs (not in the typical sense, haha, it acts like theres a short) wiggle wires whatever, but not all the time, its INTERMITTANT.... I hate it when that happens, and it only seems to do it for a while when its warming up and every so often when just playing or tweeking the knobs. When I unplug the guitar cable and replug, it seems to clear up. I thought it was a ground related issue, but everything seems tight. Maybe an LDR isuue? Its got me badafflefarted!

Its like theres dirt in the pots or a bad ground, but I have checked that and when its not doing that, I cant get it to do it.

Has anyone experienced this problem or know of any trouble shooting tactics I could try? I don't want to take it to Mesa, they take forever and charge a arm and a earlobe. Its a 91 IVB version. If anyone has any ideas or suggestions I would be very greatful.
thanks
Ed

[Don Moose]

Is there some _particular_ knob that does it, or some few and not others?
Do knobs NOT associated with the lead mode do it?

I'm wondering if one or more of the pull switches is going goofy and affecting one or more of the LDRs.

Hope this helps!

[edge59]

Its the Lead gain knob. I just swapped it with another and so far it seems to be holding. I also had to swap V2 it was getting noisey. I will take it to a jam tonight and see what happens. I have my old T-rusty Fender Deluxe Reverb as backup.
I bought this used and I think the previous owner dropped the head. One corner of the back chassis weld is broke and I see where one of the wood footswitch mounting blocks on the back is cracked..... I hate buying someone elses problems, he said nothing but his guitar fell against the gain knob and sheared it off. He sent one with the amp, and I changed it, but its a good thing I bought another 1meg pot for backup. So far so good, I will report back how it goes. Now I hope there are no other issues.
thanks
Ed

[edge59]

Its fixed, the lead drive pot was faulty. The new one works great!
Thanks'
Ed