Marshall SL100 Bass Knob Not working

[thelaughing]

I have a marshall super lead 100 head that seems toe be lacking some low end. I noticed that while the middle and treble tone knobs alter the sound significantly, the bass knob seems to be useless. For some reason its not working, no matter which way I turn it, the sound doesnt change at all.
I will likely take this in for repair, but I have it opened up and would love to see if this is something possibly easy to fix. I am considering bypassing the bass knob altogether hoping that might bring some bottom end. Anyone have any thoughts on this? Is the problem possibly not in the actual knob circuitry at all?

[pontiacpete]

Be careful with the amp open ! , be sure to unplug and discharge. High voltage in that amp can kill you.
Once you've done that, changing the pot could be something you can learn to do.

[thelaughing]

safety first indeed!

yeah, im trying to avoid death and paralysis first and foremost. I want to start learning to perform modifications and repairs, partially because I play out a lot, and every amp repair guy in my town spends weeks with the amp at a time. Is it safe to assume though, that a bad pot is the culprit?

[pontiacpete]

Get the schematic here.
Marshall Amp Heaven Schematics - JTM-45 JCM-50 JCM-600 JCM-900 JCM-2000 JTM-100 JMP IBS Jubilee Valvestate Bluesbreaker

You can check the pot with an ohm meter. Put probes on the lugs and see if it's changing in resistance... is one thing you can do,