I have a Nakamichi AV10, and it's been good. But when I use it for a while, at fairly high output, the volume starts to fluctuate or "pulse" up and down. Almost like a sine wave, loud, softer, loud, softer.....
There's also the issue of zero output from the A set of speakers, the left channel. I've just switched to the B outputs to get around that. Still, nice to solve that one, so I might start with contact cleaner in the speaker output switches.
I've started to look for a repair depot in my city, and will likely go that route. But I'd also like to have some decent idea what the problem could be, before I even approach a repair guy, and at least 2 friends feel it's the power supply, possibly the capacitors getting weaker with age. I think the amp is 25+ years old, so is this possible? Do large electrolytic caps weaken with age?
Other possible issues that come to mind, cold solder joints that could use re-flowing, intermittent broken PCB track, output transistors. That's about all I can guess at.
I'll open the casing tonight and do a few long overdue items, like clean dust out of the heat sinks. And look for obvious burn marks, or iffy solder joints. I also see that many of the identical power transistors are still available on Ebay, as are the large caps that might be losing their mojo. The best Nak AV10 maintenance website I've found in my searches, is by Peter Vis of the UK, and he doesn't get too detailed, but his 10 page look at the components is a pretty decent start. www.petervis.com/Amplifiers/nakamichi-av-10/nakamichi-av-10.html
He really stresses cleaning out the cooling fins reasonably often, and at a glance, this makes sense. Dirty heat sinks, really caked with dust, could cause overheating.
Anyone have any other guesses about the cause of the problem, based on this minimal description? I know this is an exact science.
Thank you, Tom.