FW: [TekScopes] Tek 2712 Battery circuit


Larry McDavid
 

What's this all about?LarrySent via the Samsung Galaxy S20

-------- Original message --------From: Howard Hoyt <Elecraft.KX@gmail.com> Date: 1/23/22 10:28 PM (GMT-08:00) To: TekScopes@groups.io Subject: [TekScopes] Tek 2712 Battery circuit Hi all,I have a Tek 2712 SA made in 1993.  In 2020 I replaced two original failed backup BT600, 3V, 0.17 AH @ 0.85 mA button cells (Tek p/n 146-0044-00) which had lasted 27 years!  As I had trouble locating the original part and they were described as 3 V LiMno2 cells, I replaced them with a much bigger BR3032 which is a 3.0 V 0.50 AH backup battery of LiCFx chemistry which is supposed to have exceedingly low self-discharge, indeed they are specified for pacemakers...but I only got shy of two years before they failed...and surprisingly were discolored and had leaked (!) but caused no PCB damage.Regarding the circuits they are in: the cell on the GPIB board is isolated from RAM by the Dallas DS1210 and a diode in parallel with the DS1210's internal power path.  The identical cell on the Display Storage board is merely diode OR'ed with the +% rail.  Given they are isoated in two different fashions, it is unlikely the short life and discoloration on the replacement cells indicates the 5 V rails were somehow being applied to the cells, destroying them.  I have tested the diodes and they are good.  In an abundance of caution I have ordered a DS1210 as well.I have a few questions:1) Has anyone seen a similar situation with these DS1210s and battery damage?2) Has anyone else see the LiCFx cells leak and discolor?2) The original cells are 3 V, would there be a problem using the well-regarded Tadiran TL-5903/0P 3.6 V Lithium cell instead?I appreciate sharing any and all experience with this kind of situation.Cheers,Howard Hoyt