new member, old amp, need help

[xris]

I have an old Kustom solid state head that I got from a Bandmate a few years ago.  The problem is when i power on the amp, the volume is very low.  My bandmate used to remedy this by hitting the top of the the amp, which would gradually bring the volume (and tone) up to where it should be.  However, this no longer works.  Any help would be much appreciated as I gig quite heavily but cannot afford a new amp at this time.

[Enzo]

If the amp has either FX loop jacks, pr jacks marked send and return, OR if it has preamp out and power amp in jacks, try plugging a spare cord from send to return, or from preamp out to power amp in.  ANy help?