Janus 100w Suitcase amp keeps blowing power amp module fuses.

[blueberryjam]

Hey everybody. Bought a new suitcase Rhodes (Janus 100w) in may. After a few days the right speaker stopped working and I noticed that the fuse was blown so I replaced it. From the day I received the Rhodes there was a quite loud hum in the right speaker so I then took the amp to a tech. He couldn't find the issue so he swapped the power amp module with a newer one he had and that fixed the hum. But a couple months later and today the same fuse has just blown again.  so it blew with two different power amp modules connected to it.

Any idea what could cause this ?