Mark III Strange Behavior

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ManCas

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Oct 16, 2009
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Hello guys, I've been lurking for a while around the forum, but recently I'm having some issues with my "new" Mark III.

I received my amp in great condition about 2 months ago and have been gigging with it ever since (using it almost every day). A couple of days ago, after a gig, I switched to the R2 channel and there was very little volume and drive, I cranked the R2 volume pot (mod) and got a little more volume but nothing even close to "normal" levels.

Naturally I swapped all preamp tubes but the problem persists (I noticed that V1 glows less than the rest of the tubes, they are the same brand and model, this continues even after changing the tube).

After a while I noticed this: If I turn the BASS (3-4+) knob up, the volume decreases, it does the same if I turn VOLUME up (7-8+) while in R2 or Lead channels.

Do you have any opinions or guesses? Thanks a lot in advance and Happy New Year!

PS: I can get a setting where all 3 channels work fine, if I set Vol at 7 and Bass at 2 or 3, but I normally use the Vol knob almost cranked. EQ works just fine.
 
sounds like it needs professional help. These things are close to 25 year old now. My guess is that there are some capacitors that need replacing.
 
Hi man, thanks for the reply. The amp actually had a cap job about 2 years ago, at Mesa. Tonight, I'll get some WD-40 to check if it is a bad contact on some preamp tube (V1 or 2, most likely). Cheers!
 
Holy crap...DON,T USE THAT STUFF!!! i,ve seen more amps f**^ed up with that stuff than i care to mention.You need electrical contact cleaner such as servisol!!!
 
lol, I decided to check the thread before doing anything!..I'm glad I did..thanks for the heads up man!
 
No problem, i,ve got an old mark 2a with graphic eq that,s f***ed because someone must,ve sprayed the old dreaded wd-40 on it,your not alone many people think that stuff is a cure all for everything.However a can of contact cleaner is worth it,s weight in gold with older boogies, the fx loop in particular is prone to trouble which can cause the amp to cut out, spray with some cleaner and viola...glad i helped.
 
Although any contact cleaner works, I find that this stuff works the best.

http://www.stewmac.com/shop/Tools/Special_tools_for:_Electronics/DeoxIT_Pot_and_Switch_Cleaner.html?actn=100101&xst=3&xsr=2716
 
Thanks for the replies guys, but it didn't work. Took it over to my tech, he says it's must be the switching system, but I don't think so. I just emailed Mesa to see if the can opint me in the right direction.

Im in South America, so shipping the amp to the States is kidn of my last resort. I'll keep you posted!
 
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