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mole42uk · 26th Sep 2018, 6:38 am

The meter passes it’s own self-test and allows the various test functions to happen so I’m fairly confident that the processor and memory works.

Checking the power supply reveals an oddity. The 5V is spot on, but the negative rail around U117 is pulsing at about 2 c/s and doesn’t seem to produce the required -7V. There’s an inverter at U101 which has no output although the +5V supply is good, it’s negative rail is tied to the -7V which might be stopping the inverter. I suspect there is something dragging the -7V into overload so that the regulator is shutting down.

Further checks will reveal more, I’m sure.

26th Sep 2018, 6:38 am	#5
mole42uk Nonode Join Date: Aug 2010 Location: Resolven, Wales; and Bristol, England Posts: 2,608	Re: I've injured my Keithley 175 DMM The meter passes it’s own self-test and allows the various test functions to happen so I’m fairly confident that the processor and memory works. Checking the power supply reveals an oddity. The 5V is spot on, but the negative rail around U117 is pulsing at about 2 c/s and doesn’t seem to produce the required -7V. There’s an inverter at U101 which has no output although the +5V supply is good, it’s negative rail is tied to the -7V which might be stopping the inverter. I suspect there is something dragging the -7V into overload so that the regulator is shutting down. Further checks will reveal more, I’m sure. __________________ Richard Index: recursive loop: see recursive loop Last edited by mole42uk; 26th Sep 2018 at 7:07 am.