about 71B's CMT 64K RAM modules

about 71B's CMT 64K RAM modules - Printable Version

+- HP Forums (https://www.hpmuseum.org/forum)
+-- Forum: HP Calculators (and very old HP Computers) (/forum-3.html)
+--- Forum: General Forum (/forum-4.html)
+--- Thread: about 71B's CMT 64K RAM modules (/thread-2391.html)

about 71B's CMT 64K RAM modules - patrice - 11-04-2014 10:52 PM

Hi all,
I am loocking for the references of the CMT 64k RAM battery.

[Image: 64K-RAMx.jpg]

images posted by Mike: http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv014.cgi?read=49425

RE: about 71B's CMT 64K RAM modules - Sylvain Cote - 11-04-2014 11:49 PM

(11-04-2014 10:52 PM)patrice Wrote: I am loocking for the references of the CMT 64k RAM battery.

Bonjour Patrice,
J'ai le même module et comme toi je cherche une batterie de remplacement.
Si tu trouves l'information s-t-p indique-le sur ce site.
Je fais la même chose si je trouve l'info en premier.
Cordialement,
Sylvain

For our english speaking friends ...

I have the same module and also searching for the battery model.
If you find it, please report back the information on this site.
I will do the same if I am the first to find it.

RE: about 71B's CMT 64K RAM modules - Garth Wilson - 11-05-2014 03:17 AM

I believe I took the battery in mine out a few years ago and just left it out. It was 20+ years old and still good because it never got used since the 71's own batteries keep the memory alive as long as you don't unplug it, and I wondered if it would leak before the next time I check (which might be in another 20 years). As long as you never need to unplug the module, I think you can just go without its thin battery.

RE: about 71B's CMT 64K RAM modules - Geoff Quickfall - 11-05-2014 04:40 AM

With the 71b off; plug in the wall wart (adapter) and then swap the four AAs. This keeps the internal ram loaded and should keep the CMT ram loaded while you change the AAs.

I think the internal CMT battery was for memory retention in case the AAs died and to give time to change the AAs.

RE: about 71B's CMT 64K RAM modules - rprosperi - 11-05-2014 05:04 AM

(11-04-2014 10:52 PM)patrice Wrote: Hi all,
I am loocking for the references of the CMT 64k RAM battery.

I have a copy of the "Instructions" that came with the CMT RAM modules (7 not really useful pages) which describes the battery; it shows insertion (should be 'hump' side up) and polarity (the 'hump' is plus (+)) but does not specify voltage, model # or any specs. It also clarifies that the battery is only used to retain RAM in the 64K modules while outside the 71B; while inserted, all power comes from the 71B.

Sorry it's not very helpful.

RE: about 71B's CMT 64K RAM modules - Garth Wilson - 11-05-2014 08:23 AM

(11-05-2014 04:40 AM)Geoff Quickfall Wrote: With the 71b off; plug in the wall wart (adapter) and then swap the four AAs. This keeps the internal ram loaded and should keep the CMT ram loaded while you change the AAs.

I think the internal CMT battery was for memory retention in case the AAs died and to give time to change the AAs.

I expect the same internal capacitor keeps the module RAM going as what keeps the internal memory alive when you change the batteries without plugging in the wall adapter. Someone else might know more about it to confirm; but I have never had the wall adapter in when changing batteries, and have never lost memory when doing it. I change one at a time to minimize the time that it's disconnected from the battery power, something you can do with the 71 but not the 41, since the 41's holder requires removing all batteries at once.