Mark III problems

Mark I's, II's, III's and the almight IV

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Brain Becker
Bottle Rocket
Posts: 8
Joined: Thu Nov 27, 2008 2:25 pm

Mark III problems

Post by Brain Becker » Fri Jan 16, 2009 8:24 pm

I have a red stripe Mark III that is "static-y" when I let chords ring out. I have replaced all of the tubes, cleaned the tube sockets, input jacks, and all of the pots and I'm still having the same problem. Does anybody have any suggestions as to what to do next?

acorkos
Mark II
Posts: 129
Joined: Wed Oct 01, 2008 3:52 pm
Location: 2 x MkIIB-4-Me

Re: Mark III problems

Post by acorkos » Sat Jan 17, 2009 8:58 am

make sure your guitar, guitar cable, speaker and speaker cable (and jacks, both amp and cab) are ok....substitute each with another and make sure the static is still there.

you might have a loose component on the board somewhere.

what i would do is pull the chassis, fire it up, plug an ipod into the main input jack, and then with a wooden (non-conductive) stick, carefully poke around, tapping on each component and solder joint...a loose connection will usually reveal itself when you push on it. remember to use care because the voltages inside the live amp are lethal.

while tapping pay attention to color of the resistors....you may have one burned open and the charring is pretty noticeable

do you have a digital multimeter? with the amp off, measure resistance on the power tube screen and grid resistors, and power supply voltage dropping resistors. look for drifted values, open and shorted resistors. with the amp live, measure voltages at pins 3, 4 and 5 of the power tubes, pins 1 and 6 of the preamp tubes and compare to the schematic.

this is a good resource:
http://www.geofex.com/ampdbug/ampdebug.htm

Brain Becker
Bottle Rocket
Posts: 8
Joined: Thu Nov 27, 2008 2:25 pm

Re: Mark III problems

Post by Brain Becker » Sat Jan 17, 2009 9:58 am

I don't have an Ipod, but I do have a meter. When I get some time, I'll poke around and post what I find out.

Brain Becker
Bottle Rocket
Posts: 8
Joined: Thu Nov 27, 2008 2:25 pm

Re: Mark III problems

Post by Brain Becker » Sat Jan 17, 2009 10:00 am

I'll add that I know it's not my guitar or cables because I don't have any of those problems with my other amp.

nor
Mark II
Posts: 117
Joined: Sat Oct 29, 2005 7:35 pm
Location: Phoenix, AZ

Re: Mark III problems

Post by nor » Sat Jan 17, 2009 11:02 am

Sounds like a dirty pot.

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