Having a few odd problems...

[rydogg_sc2]

..and I was wondering if any of you have experienced anything similar or have some advice for a new Mark V owner. I will cut and paste my email that I sent off to Mesa this morning to show my problems.

I am having a few problems with my new Mark V head. I have one by one replaced all the preamp tubes with a known good to try and diagnose these problems with no success.

1. The reverb when on in channel 1 has a very noticable buzzing/hum sound.

2. Channel 2 when the EQ is not engaged has a loud persistent hum.

3. Anytime the EQ is engaged or disengaged, be it with the footswitch or front of the amp, there is a very loud thump sound that hits you in the chest.. This is not a small channel change type thump but a very loud one.

Any advice would be greatly appreciated!

 

[pivot]

Sounds like allot of problems I would call Mesa they are really good.

 

[Monsta-Tone]

I've seen failed coupling or tone caps cause odd behavior in old Mark IV's.
Do any of your tone pots (or EQ sliders) make very loud scratchy or static like sounds when you move them?

I would definitely call Mesa this morning. They have always been super helpful in the 10 years + that I have been calling them.

 

[rydogg_sc2]

After I got off the phone with Mesa, in a backwards way, I discovered myself something is messed up with the EQ section. If the EQ is turned off it is still changing the tone of all the channels. That goes for the preset or 5 band section depending on which one is selected. Something going on there must be causing the thump when turning it on and off and the it is also causing the hum in channel 2 because I run the eq off in that channel and the lowest slider in the 5 band eq is completely controlling the amount of hum present even when the eq is switched off.

Correct me if I am wrong but when the eq is switched off the presets or 5 band should have zero impact on the tone correct?

So it is a pretty odd problem and I will probably have to send in my amp to get it fixed. Booo :x I will call them back tomorrow and tell them my new findings as they were not able to pinpoint the problem on the phone with me today.

 

[bandit2013]

I would try two things.
1. if you can, disconnect the reverb connections next to the output transformer. One of the cables may be picking up noise that would influence the audio signal. You may want to relocate the amp to a completely different outlet, possible that something is operating off that circuit that causes the hum. I get a similar issue with my amp when the dishwasher is running (I can hear motor noise in the speaker and is influenced by the guitar pickups).

2. Disconnect the footswitch cable from the back of the amp. Check to make sure it is an 8 pin cable. Also try again without the footswitch connected to the amp and see if the EQ issue is resolved.

If the above basic tests do not help, consider Mesa Repair under warranty.
It is possible that something is not connected properly or a wire is crossed on one of the pots or circuit boards. Mesa used many ribbon cables with connectors, some parts are connected to link from the controlling device to the circuit board, etc... If there is something bent or shorted internal to the amp, that should be covered under warranty. Even some of the wires that are bound together if not routed properly will also result in the issues you are describing. That should be handled by Mesa.