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Colour Classic dark and cold, salvage attempt, MB recap and boostrapping

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  • 68kMLA Supporter

from https://68kmla.org/forums/topic/62716-colour-classic-1993/


Hi all,


ok, I recapped the MB (I removed the ROMs for the cleaning process)

I was wondering how to bench test the MB

Why don't I just snap it in? Because I've not yet finished recapping the PSU/AB.


I was not able to find the pin out of the left connectors: from top-down: the first 5 pins are +5,+5,GND,GND, +12 (it should power up the MB), the second (hair comb style) is the HD , the second the FDD. Still I miss the video signals and speaker.

I feel clumsy with this machine, I feel more comfortable with LCs, Plus, SEs.

Can someone please redirect me where to find documentation?


Also, I read this Mac has an hybrid soft-power on, PSU switch + keyboard button. Can it be bootstrapped like the Mac II?




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  • 68kMLA Supporter

@bibilit ah! Thanks pal. this is interesting!! Now I need to know how to feed the MB with voltage: are the 5 pins on the top most connector (relative to my photo)?


more about the AB+PS:

I replaced all the capacitors recommended by Bruce.

During bench testing the voltage are unstable, shifting from +3.5 to +5, and from +8.5 to +12 on the HD pins, apparently the +5V and +12V are available without soft power.

The voltage are shifting also at the beginning of the low voltage section, just after the flyback transformer.

I tested the optocoupler (I identified a diode in on side and a transistor on the other, I can not do more then this), I replaced the regulator. no improvements.

I checked all the solder joints, they look just fine.

I'd go for replacing the MOSFET now but I'm going blind, I can not make better diagnose.


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