Accuphase M-60 Love

[User211]

I'll check it out as per Claude's advice.

Essentially if this is the issue, and Claude has been telling me it isn't and it's my measurements until now, then it's pretty much the same failure I found in that 211 monoblock I fixed a while ago, Barry.

[Barry]

Any success with the diode measurements Justin?

[User211]

I haven't had the time, Barry, or enough will to make the time. I have pencilled in Friday for investigation.

[User211]

The diodes are fine, Barry.

I did go as far as isolating one but IMHO that was a complete waste of time. Each package appears to contain two diodes connected to a common pin. Each measure 500mV isolated one way and massive resistance the other.

Isolating is just a fools game despite AI insistence. Why? Because in-circuit you can see the diodes charging up caps one way round with the diode probes, but not the other.

We just need to see how one mono behaves differently to the other.

I could post a load of stuff showing Claude talking rubbish about this, but it is pointless. It came round to my way of seeing it eventually.

That said, I did learn a bit from doing this.

Still perplexed I haven't sussed this out yet. The poor old Accuphase is turning into an amateur's test bench.

I need to get that tranny back in and reinstate the diode network. Not looking forward to the tranny loads of wires to do.

[Barry]

Curiouser and Curiouser!

So the transformer is OK, and (both?) the diode packages are OK. That leaves the large reservoir capacitors and the four disc ceramic capacitors to check.

If they all check out OK, then the only thing left is to detach the amplifier supply rails from the capacitors to see if the capacitors retain their voltage.

[User211]

There isn't much I haven't checked, or at least think I have checked as being fine with an LCR and multimeter with no power applied.

I will put it back together and send Alan a PM when done.

[Phil M-W]

Justin, looking at the pictures I can see that the diode packs appear to be isolated from the chassis with mica washers and some thermal grease. It would be worth checking that the washers are not damaged (perhaps have pinholes in them or a piece of swarf punching a hole through them). Since the metal bodies will be connected to the DC rails, a short there will pull the transformer outputs down to a diode drop above the chassis potential, presumably ground. I don't know if this area has been disassembled previously but if the thermal grease has been replaced, somebody may have used silver loaded grease, typically silvery grey in colour, and popular for use with CPUs and heatsinks in computers, relatively cheap and very readily available. This grease is (highly) electrically conductive and if carelessly applied can bypass the insulating washers. The correct grease would be aluminium oxide loaded grease, which is white.

Just my 2 cents.
Phil

[User211]

Phil, I just got continuity to chassis for literally a second or two from the base of one of those diodes using the continuity tester on my multimeter, which admittedly is a cheap Maplin job that is probably 30 years old.

But then it just goes/disappears. Even after discharging the orange caps you can see in the pics.

I thought software was hard but I really am realising hardware can be an absolute bitch.

Sometimes, you just need to hire someone who has been in the field for a few decades and pay for what they know.

At least, that's the conclusion I am coming to for this case.

These things are worth saving because they quite literally are outstanding examples of their ilk for the time period.

Like the best classic cars.