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Today's experiment: supplying Alice's Vbb from an external source. I wanted to test the behaviour of this 1200 without the +/-12 V supplies (only +5 V), so I wired up a connector and hooked it to my bench power supply. Since I have a second output on this supply, I set it for 3 V below the ground for the 5 V supply, and connected it to one end of C2X (which I'd also replaced with a 10 uF electrolytic cap with a 100 nF ceramic in parallel).Results:Running without +/-12 V makes no difference to the glitch, the health of Vbb or the CCKQ clock signals. Running with the extra capacitance also did not help noticeably. But supplying a negative voltage to Vbb seems to keep the CCKQ signal good and allows the system to keep running! If Vbb rises above about -0.8 V the CCKQ signal goes bad, but if Vbb is lowered again below -1.5 V, it comes right again. Alice doesn't draw any appreciable current on Vbb.Overall power consumption was about 1.57 A @ 5 V (7.85 W), and interestingly, improving the Vbb strength (lowering the voltage from -1 V to -3 V) makes Alice run cooler and with lower current draw from the 5 V supply.I'll need to test a bit more and figure out how to make this a permanent fix, but it's looking hopeful that I now have a working 1200. I've tested it today with internal and external floppy drives, a mouse, but no keyboard, and so far no demos or games I've tried have shown any unexpected issues.
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Topic: A1200 post electrolyte damage: Alice overheating? (Read 10801 times)
