Mesa Boogie MK IV

Too many controls on a Boogie’s front panel for me to be a fan but people seem to love them.

This one below was cursed with a strange fault of bias instability which would lead to humming as the bias drifted off and ultimately to red plating after 30 mins or so.

The cause of the fault was some sort of PCB contamination. I initially thought that this was some sort of chemical residue on the PCB but after much cleaning it didn’t really improve.

In some conditions the amp would actually spark as voltage jumps between worn out circuit pcb paths as in the case of the bias supply or worse when adjacent parts of the pcb are a little too close. Then unrelated HT would jump to say a channel switching circuit. Take a look at the videos for examples of this.

The solution in this case was to remove affected parts from the PCB and mount them off the board following point to point construction methods. The challenge here is the space. Boogies are famous for cramming a lot in so it is a very cramped working environment.

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