Mark IV combo fuse issues, need your help!

[malexyss]

Hi everyone.

I own a european Mark IV combo, and I have fuse issues (220V) :
The fuse blow sometimes when I start the amp, and more surprisingly, when I switch it off. I can't understand why and I find nothing on the web. The amp is in the hand of my tech, who didn't figure it out by now. All the tubes are okay, the fuse is the correct one (2A Slow Blow). It only blows when switching on or off, but when the amp is on, I don't have any problem, it works brilliantly.

I really need your help, I can't play it for a month now, and I need it to record a EP.

Thank you very much.
Bye

 

[stokes]

"The fuse blow sometimes when I start the amp, and more surprisingly, when I switch it off."
Do you mean the main power switch or the standby switch?When a fuse blows,something is shorted.If it is happening when you turn the main power on with the stanby switch "in standby",the only thing drawing current is the PT and rectifiers.Just looked at the schem,the first or main filter cap(s) are also "in circuit".I would suspect one of those 3 components.PT,rect.,or main filter.

 

[malexyss]

Hi Stokes. Thanks a lot for your answer.

Yes it happens with the power switch, not the standby one. Once the amp is on, I have not problem at all. I'm sorry I'm a french guy and I don't unterstant what a "PT" is ?
The Mark IV has no rectifier tube so the problem can't be this one. I take not of the main filter.

Thank you very much.

 

[stokes]

The PT is the power transformer.It doesnt have a rectifier tube,but it does have a rectifier.When you turn the main power switch on,the mains voltage connects to the PT,which in turn delivers voltage to the rectifier and charges the main filters.The standby switch disconnects the dc voltage from reaching anything else in the amp.Maybe time to find a different tech.

 

[malexyss]

So I got news ! I contacted Mesa Boogie via Facebook, and amazingly a guys answer to me. He told me to try my 220V Mark IV with a 2,5 slo boo, instead of 2. And it worked.

So my problem is solved. Thats explains why the tech didn't find anything wrong with the amp.

Cheers !