[time-nuts] PM6681 and Timelab (was: PM6680 or 53131A for TimePod)
holrum at hotmail.com
Wed Nov 18 19:41:59 EST 2015
I once got in around 20 Tek DM5?? GPIB DVM modules for the TM5000 series mainframes. They have a rechargeable nicad pack soldered to the circuit board. All the meters still had good cal data but the cells were on their way out. The meters are a pain to re-calibrate...
I used a DIP clip to provide voltage to the SRAM chip while changing the battery. Only lost cal dataon one meter. I replaced the nicads with a CR123 lithium cell with a series diode to block the charging current. On each meter I checked the standby current to the SRAM first. A couple had rather high values that would drain the CR123 after a year or so, so I kept nicads in those. After 5+ years the meters are still working on the CR123 cells.
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