On Tue, 15 Jan 2013 06:50:24 -0800 (PST), j
wrote:

I'm trying to troubleshoot a 1980'2 era Nak receiver that has pushbutton input switching via a microprocessor (can also be remote controlled). The button lights don't work, and I get no input connections at all. Strange, but the micro works, controlling the volume up and down. Also, the amp works via the pre-out and power-in jumpers. Apparently, some aspect of the switching (done via an analog switch IC) is screwed up. Anyone have ideas on how to troubleshoot this?


I would first check the electrolytic caps in the power supply. Noise
on the B+ lines will cause all matter of digital problems with this
model. Chuck