Mark IV troubleshooting, popping, volume fluctuating

Hi all,

I was hoping for some troubleshooting help with a Mark IV.

An array of symptoms: crackling, popping, sudden jumps in volume. Sometimes the amp will remain quiet and volume level like it should be, then other times it will do what it wants to do. Affects all channels. I can twist the master volume while it's doing its noisey thing but that does not alleviate the symptoms. Tapping the front of the amp (firmly) can sometimes bring the amp back to normal.

What I've tried: replaced power and pre amp tubes independently, tested in simulclass and class A, jiggled and tapped preamp tubes. No changes, same symptoms.

Any ideas?

This is a IV B, if that helps.

Thank you. :?:

Lots of things can cause the symptoms that you describe. Take it to a good tech to find which one is causing the problem.

With my Mark IV, the push-pull pots had worn out (although they did not make scratchy noises when they were used). Once the first one was found, I had all of them double checked and the faulty ones replaced with new ones from Mesa. If I recall correctly, 3 or 4 of the gain/drive pots were replaced. I guess they had the most use from previous owners.

There are less expensive pots available, but most of the cost was the technician's time. So I insisted on Mesa parts to avoid return visits. And I kept the paperwork so the amp would retain its resale value.

Took the amp to a tech as recommended above, turned out the tube sockets needed some tightening up as they weren't making good contact. Just thought I'd post this in case someone runs into the same issue.

Hey, thanks for posting the results. This makes the Boogie Board so much more valuable. It's rough reading a thread about a symptom your amp may have - only to find out the OP never responded with the results.

Thanks for taking the time to update us!

Any update? My Mesa Mark IVb combo is also experiencing random volume jumps. It'll last for 15 seconds or so then drop back down to normal. The tone changes to a bassy/hallow sound during the spike.