replacing 71b batteries without losing data

[rprosperi]

(07-14-2023 02:46 PM)KimH Wrote:  Glad that I coincidently was able to help - looking forward to your posting on the tube.

Maybe I was simply lucky, Bob is pretty much always spot on with his responses!

Very gracious of you, but sadly not really accurate...

I am quite surprised by your comment that you can remove batteries for several minutes without losing MAIN RAM (though IRAM/Port RAM indeed is rarely lost) as this is not my experience, certainly for the last 20 years or so; my memory of such details in the 80s are a lot less clear, but I do recall learning the lesson back then to always connect power first.

But a comment you made in your reply notes an important distinction I should have made. My comments about hardly ever succeeding in not getting an ML when changing batteries w/o adapter power refer to units when they will no longer turn on, or when the BAT annunciator has been on for a while. There seems to be a short period when the unit won't power-on, yet RAM is maintained; it is essential to have power connected when in this state.

When replacing still-good batteries, it is possible to replace them quickly, one-at-time, and not get ML, probably about one time in 4-5.

Regarding EPROM modules, contact me off-list, I'd be happy to burn one for you.

@Garth - Have you tried this recently? Next time you have to change batteries, please give it a try and report back here. I suspect 71B units have reduced their capacity to maintain RAM over the decades, and it's far less likely to be preserved today.

As for the 41C, that's an entirely different situation, indeed they will sometimes last many, many hours w/o a battery pack installed, though they will often lose the time. But if you change battery packs quickly enough, you can swap w/o losing time. I keep a stack of 41C battery packs loaded with new batteries so I can swap one within a few seconds. With nearly 20 41C/CV/CX machines it seems at least once a week one of them needs batteries. It also took me a long time to learn that when swapping batteries with a 41CL, you must [XEQ] "MMUEN" after powering back up to restore the MMU configuration.