Author Topic: Restoration glory of Keithley 2001 DMM  (Read 221265 times)

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Offline openloop

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Re: Restoration glory of Keithley 2001 DMM
« Reply #750 on: April 15, 2019, 10:23:44 pm »
Looking at the schematics, it appears that the main CPU gets its line readings straight from main power transformer taps. Digital board's U628 (page 2 of addendum part 2) is a comparator which detects zero crossings and feeds them straight into the CPU (pin 56)   
 
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