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I tested my optocouplers with a multimeter set to diode mode (so you can get the forward voltage). You can also use a multi-tester or simply desolder and wire up to a test circuit. It was the transistor side of my opto that failed and a cheap multi-tester picked that up whilst it was in-circuit...

I'd be surprised if you get mains ground continuity on the PSU->Logic board connector. The secondary PSU board is a DC-DC converter, so it should be isolated. If you have a PSU issue its worth first checking for the 12V supply on the PSU connected to the logic board. From memory the black...

Thanks Traq, that's some good illumination. I was planning on overclocking a 475 and 575 anyway, so that seems like a simpler solution than trying to work a new chip into the mix. I'd still be interested if anyone has pictures of the later Daystar 68040/601 version of this card I've snagged.

Sorry to resurrect this thread. I have just acquired and 'repaired' a 475 that had the Apple 601 upgrade card installed and was interested to know if any comparisons to the Daystar + Clock/PLL circuitry have been made?

I use https://gitlab.com/DavidGriffith/minipro installed via homebrew. Works well but it is command line only.

That's interesting that your Q630 had a speaker stamped with 16Ω - the one in my LC630 is stamped with 8Ω. You can get a rough measurement of the impedance with a multimeter set to resistance on these smaller speakers.

FYI: For the speaker, I've put together a STL of the speaker case and it seems you can find 70x30mm 8Ohm speakers from a few sources. The STL is linked to this 68kmla thread - and I can change its parameters reasonably easily if anyone needs/wants different variants. Interestingly the speaker...