Accuphase M-60 Love

Back on the job. Just trying some cross comparison unpowered checks between working and busted units. Now using Claude to try and suss it as Grok said it was best at electronics.

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Spent 3-4 hours cross checking these driver boards. There are some discrepancies in values between about 4 components I have duly noted.

I don't reckon they are massive enough to be the issue.

Logic is pointing to the transformer primary and indeed Claude thinks that's it. But my in-circuit super basic cross comparison tests say no.

The working mono still has the 2.2 Ohm 20W resistor from 1976 near that power switch, the one that keeps blowing in the non-working mono that had already been dogdily replaced before I started looking at the issue. That means this problem has happened before in all likelihood. Without replacing the transformer, or so it seems.

Gonna get the tranny covers off and have a look to see if one looks different to the other. I have another idea. Will the working mono work with the busted mono's protection and driver boards?

This is proving to be a really likeable problem:) I just love it when I haven't got a fucking clue what is going on;)https://uploads.tapatalk-cdn.com/202...2cc89e39c2.jpghttps://uploads.tapatalk-cdn.com/202...170d3501d7.jpg

Great work Justin, been a while since I checked into this thread. I really hope that you managed to get these sorted. :thumbsup:

Not great work yet.

Claude is effectively very good at admitting it isn't sure about much. It's not the AI for this problem, despite what Grok said. And its analysis of circuit board pics is below average and it knows it.

Copilot has just come up with a great transformer primary test. I think it is onto something. It agrees with me that indeed it is not a primary winding short issue.

I'd explain it but it's a ball ache post that most would not understand or read but there is a notable difference between the two monos that is significant I believe.

Replacing a transformer is not a job I want to do. But I probably am mad enough to get some bespoke ones made if needs be. The issue isn't the money, more the hassle factor.

ATM it is not looking like it is needed thank god.

The red wires in the pic are secondary transformer outputs that should have 64.5V on them to feed a couple of diodes in the rectifier circuit. These should sum to give 129V across the diode terminals. In the working amp they do, in the busted one they don't - it's 0V.

Which implies the secondary is open circuit in the busted amp.

Fingers keep pointing at the tranny. https://uploads.tapatalk-cdn.com/202...c21d3b8365.jpghttps://uploads.tapatalk-cdn.com/202...ad802540b4.jpg

That's a bit of bad luck with a faulty tranny, but at least you have found a fault.

How many other secondary windings does the transformer have, and what are their voltages? You might be able to find a replacement, or at least have one made.

Quote:

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Originally Posted by Firebottle

That's a bit of bad luck with a faulty tranny, but at least you have found a fault.

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Yeah. I think it went from short to open circuit as it was blowing that resistor I was on about. But it isn't anymore.

The blue and brown wires are two more secondary outputs that seem fine, Barry.

I will take the tranny cover off tomorrow and prey it's an interface fault between the tranny and the red wires but I highly doubt that even if AI thinks it is likely.

Whilst the M-60s can dump a shed load of power into the Apogees, it really does get extremely hot doing so. It's probably been killed by repetitive heat/cool cycles. Or a transistor took it out, maybe. I will probably never know.

There was an 'event' yesterday when measuring the other working amp's diodes. Massive flash and burning plus soot left to prove it. Thought I had fried the amp, but the speaker protection switch fired open and it the amp seems OK.

Gotta be careful with those probes, LOL. I'll post a pic and you will see it must have been fairly extreme. It was;)

And yes, Barry, I'll get it rewired.

Diode fire mess. Check out the leads connected to the left hand diode and the burn on the base. Wish I had it on video it was impressive!

Also transformer cover picture. It is a UK voltage unit but it can also be set to run at 120V or 100V.
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One extracted tranny. Gonna try and get a quote from trans-amp tomoz.

It's full of potting compound. Makes it a bit more challenging I would guess.

I really didn't wanna do this, but I am confident I can get it back in once fixed.https://uploads.tapatalk-cdn.com/202...3614cdf662.jpghttps://uploads.tapatalk-cdn.com/202...382f5d5fbb.jpg