Got 2275 with strong humming noise, so strong I was sure that big filter caps were done. Upon replacing them noise was a bit lower but still there. Than tested pre and power amp sections, first connecting preamp output to 2238B - and it blew 2A fuse on 2238B`s PS board instantly! 2238B lights went off but rest was working and buzzing was there. In reversed scenario, 2238B preamp into 2275`s Main in, everything worked fine. Noise is there as soon as relay clicks and volume control does not change it until around 10`clock when it gets really nasty. Did not look into preamp board for obvious issues yet, what would be a good point to start the investigation?