HP 67: charging of battery pack

[BobVA]

(04-26-2017 10:12 PM)PANAMATIK Wrote:  My conclusion: The only safe way is to run it without batteries and without charger.

Bernhard

But only when switched off! :-)

Certainly no apologies necessary! That circuit arrangement is a bit counter-intuitive and was a surprise to me as well. Thanks for your logical questions that helped me learn something!

I guess I can understand the design decision to re-use the existing AC adapter and consequently use the battery as a "jump starter" for the card reader but, as with speculation about the Woodstocks, it seems odd they didn't at least put some kind of clamping circuit across the card reader, as a bad/missing battery is a likely event.

Is it possible this wasn't much of a problem 40 years ago? Did the ACT get more fragile as it aged? I recall more than one episode of accidentally powering on my trusty HP-25 in college with a bad battery contact while on AC power and living to tell the tale. It seems they are a lot less forgiving of that today, but perhaps that's just my imagination.