I recently had this Yamaha B-2X through the shop. It’s a massive beast of a power amplifier from the late ’80s, delivering up to 170W per channel with 0.002% THD. Being somewhat more recent, this one just needed a quick tune-up as one channel’s DC offset had started to drift up to about 50 mV and needed to be tweaked back down.
Bias in both channels, and DC offset in the other channel, were all in spec. As components age and drift, small variations like these are normal and expected – that’s what the trimmers are for – and if it comes back into adjustment and stays there after some usage there’s no underlying issue. (If the DC offset returns, though, that could indicate trouble!)
Yamaha put the trimmers for both channels in a great, easily-accessible location so this was a quick job, and the amp is back in service in no time.