400+ Graphic EQ Problem

LiquidMidnight · #1 05-25-2011, 12:09 PM

I arrived at a gig two weeks ago, and upon firing up my Mesa 400+, could not get any sound out of the amp, even after trying various cables, basses, etc. I just plugged in my backup amp and played the gig.

Upon getting the amp home, I tried a few things. I first ran an outboard preamp through the FX loops and found that the power section was still alright. I tried all different preamp tubes in front. Eventually, I found out the problem has something to do with the graphic EQ. When defeating the graphic EQ, the amp performs great. When engaging the graphic EQ, the amp produces a lot of hum and has hardly any gain in the front end.

So would anyone have any idea what would be causing this problem?

Also, since I'll probably have to take this to a tech, will I have to take this to an authorize Mesa tech? I ask because I have a great tech who I know won't charge me through the nose for labor. The problem could be as simple as a bad solder joint. However, if the amp needs a proprietary part, would Mesa send it to my tech if he orders it?

Thanks!

RickenBoogie · #2 05-25-2011, 12:14 PM

Your tech should be just fine, not to worry. Just take it to the guy you trust.

LiquidMidnight · #3 05-25-2011, 02:00 PM

Thanks, Rick! I know that Mesa is pretty uptight about who sells their amps, so I didn't know if they are the same about who works on their amps. This is one of the early 400+s (it has the hard-wired power chord), so obviously it's long out of warranty. I just wanted to make sure in case my tech needed to replace something like the chipboard for the EQ and Mesa wouldn't hook him up because he's not an authorized Mesa technician.

Calaverasgrande · #4 05-25-2011, 02:24 PM

It could be that at some point something bumped the eq pcb.

It is hanging out right there in a somewhat open area that can be bumped into when you are fiddling with tubes and whatnot. The transistors or caps that are sticking up could be broken off, shorted etc.
There is also that it may need a re-cap on that part of the amp.
Personally, I like the sound of the amp better with the graphic off. It isn't that it is a bad eq. I would actually like to have one of those as a separate unit! I just think the amp has a better tone when you eq it less.
Also, give Mesa a call. While they do charge a lot for repairs they do, chances are they may have an authorized tech in your area that isnt too bad.

LiquidMidnight · #5 05-25-2011, 06:59 PM

Thanks for the info, Cala. I do know of two authorized Mesa techs I could take my amp to. Like I said, it really comes down to not having an immediate $75 (or whatever it is nowadays) labor fee just for cracking open the case. The tech I normally use is considered one of the best in the area. He's just not an authorized Mesa tech.

I actually usually use the graphic. I find it helps with more difficult rooms, and I often use it to coax a little more gain out of the amp. At the end of the day, it is a Mesa, though, which means you sometimes have to tweak it a bit to get a good sound. I know a lot of guys who have bought Mark Vs and immediately sold them because they are so complicated to set up. And some of these are guys who have used MIDI-programmable rack gear for years! Since I haven't had a chance to take the amp to a tech this week, I'm going to be using it on a gig this Friday with the graphic off, of course (and a backup just in case).