Carver TFM-15 Question

I created a basement system from all my "spare parts". Anyway, the amp was working fine but just recntly the right channel was not working when I would first turn it on. By clicking the speaker selector and/or tapping on the top of the unit the sound would come back for the duration. Any thoughts? Does this sound like a smple adjustment or do I need to take it to the shop?

Thanks!