Troubleshooting a Marantz AV9000

[Eric S]

Hi Everyone,

I've been a member here for a long time, but have been absent lately as the pace of work has increased.

I have a Marantz AV9000 that keeps blowing fuses in the power supply. It has worked for years, and then one day the fuses on the power supply board with the transformer blew. I replaced them and the new fuses lasted for 3 weeks before they blew again. I replaced the fuses a second time and they lasted only 3 days.

Figuring I was facing an uphill battle with just fuses alone, I replaced all of the electrolytic caps (26 of them!) on the regulated power supply board (some of them were truly dead), put in new fuses and put it all back together. This time, it lasted for 3 hours before it died again.

Anyone have any suggestions of what to try next?

Thanks!

[ThomasW]

Could be a bad trace (thermal intermittent) on the PCB. Only way to diagnose for sure is to put it on a scope and see what happens just before the fuses blow.

If you don't have a scope I don't know what to suggest.

[Eric S]

Thanks for the suggestion, Thomas. I don't have a scope (though from time to time an occasional use does arise). I have the full service manual (schematics and parts list), so I was thinking that the next step is simply replacing the transistors from the regulated power supply. I figured I'd start with the ones that are attached to the biggest heat sinks first assuming that they have suffered the most from heat-related stress over the past decade.

Its a shame, its a nice sounding pre-amp. While it worked after I re-capped the power supply, the noise floor was much reduced.

[Eric S]

So much for random shots in the dark - replacing the caps and all of the heat sinked transistors (mostly voltage regulators) in the power supply produced the same results. It worked for a few hours then died again. The same fuse is always blown...

[Azeke]

I would give their tech support a call, perhaps they can provide some insight.

Just a shot in the dark, have you changed to a lower ohm speaker configuration?

Peace and blessings,

Azeke