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More retro computer time!
Repair of a 1992 vintage Amstrad NC100 Notepad
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I’ll bet it’s the fuse. The power connector was strangly reverse polarity and a powersupply with center positive would blow the fuse.
That schematic of the usupply in the background looks very interesting. Can it be downloaded somewhere?
I wouldn’t have expected this thing to have such sophisticated power management. But I guess you can’t let the Z80 CPU running continuously on batteries.
Given the modest current requirement, it isn’t that hard to do. It could just be a simple boost regulator followed by a 5V LDO. The boost regulator would be set to just above 5V. When running off DC or with fresh batteries (ie, >5.25V say), the boost circuit is off and it’s effectively just an LDO with a schottky diode in series with it. As the battery voltage drops, the boost starts switching and keeping the input to the LDO high enough for it to remain in regulation.
That type of circuit can run with input voltages well below 3V but I guess they figured that by the time 4 x AA hits 3V, the cells have given up almost all their energy anyway.
BTW, the single most common generic integrated switchmode chip, the (MC)34063, has a minimum operating voltage of 3V. That computer stopped running once he reduced the supply voltage to about 3V. Hmm..
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