Pass Labs XP30 problem

I recently bought a Pass xp30 pre amp from someone. I hooked it all up and one chassis (left channel) seems to produce sound, but not the other (right channel).  I know the problem isn’t the amp and the xlr interconnect to the amp—if I switch the inputs to the amp I get sound from my right speakers. 
It was working fine for him just before I bought. I’ve checked the gain jumpers inside and they’re set to 10dB. 
Anyone who has an xp 30 have any ideas?  Thanks.