Does a battery have to be installed to use the 67 and/or 97 on the AC Adapter? Someone told me that they could not test a calculator because they only had an adapter and did not have the battery.

How useable are either of these models with only an AC Adapter and no battery?

> Does a battery have to be installed to use the 67 and/or > 97 on the AC Adapter? Someone
> told me that they could not test a calculator because they > only had an adapter and did not
> have the battery.
>
> How useable are either of these models with only an AC > Adapter and no battery?

Here is a post from comp.sys.hp48:

************************************************************

From: John H Meyers <jhmeyers@miu.edu>
Newsgroups: comp.sys.hp48
Subject: Care of old HP calcs and chargers
Date: Thu, 21 Sep 2000 07:30:21 GMT
Organization: Deja.com - Before you buy.
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I'm prompted to post this by seeing old HP calcs offered for sale
with notices such as this:

"HP25C: Includes charger and battery pack, which looks fairly clean.
Compartment is clean. When I plugged it in,
I got a flashing display, then nothing."

Plugging that calc in without a good battery pack in place
would probably have destroyed it, unfortunately.

Practically all HP "LED" calculators whose charger has
only two pins depend upon a fully functional battery pack
to absorb and filter the output of the charger, which
has no internal filter or voltage regulator itself
(it is often just a transformer, no power supply electronics
in it at all).

Without the battery pack, the transformer delivers
too much voltage to the calculator; I destroyed
one or two myself before I learned better.

Three-pin chargers (HP35, HP80, etc.) are okay
(they deliver a filtered steady voltage supply for the calc,
plus another separate charging voltage to the batteries only),
but two-pin chargers are life-threatening to old HP calcs
without fresh, chargeable batteries securely in place.

Radio Shack (USA) may still be selling "Replace-a-cell"
NiCd AA-size batteries; these have the "flat tops"
exactly like the original HP-supplied
cells ("button-top" cells are slightly longer,
and will flatten and damage battery contacts
if inserted into some calc models);
cells removed from cordless phone battery packs
(often on sale at Wal-Mart etc.) are usually similarly
without the "button tops" and if so will also work fine.

In a pinch, you can, believe it or not, bang down the
"button-top" of a couple of AA-size alkaline cells
with a hammer, to make cells which will fit and
properly operate an HP calc (but you should not then
use the charger at all, because it would overcharge
and possibly cause ordinary batteries to burst).

Knowing these facts will help to preserve and increase the value
of any old HP calcs still circulating in the market, and I hope
that any sellers who read this will profit by this information
(and "save the skeets," as Tom and Ray say :)

-----------------------------------------------------------
With best wishes from: John H Meyers <jhmeyers@mum.edu>

Sent via Deja.com http://www.deja.com/
Before you buy.

************************************************************

The HP-67 is not mentioned above but its charger has
three pins too.
I tested my HP-67 purchased from eBay some months ago,
without the accu-pack, at my own risk. It seems to work.

--

HP-67: the calculator works with no battery pack installed, receiving regulated voltage from the charger, but there's not enough current to drive the card reader.

HP-97: the calculator does NOT work with no battery pack installed, but according to HP docs, it is not damaged either in this configuration. (This is in contrast with Woodstocks, especially 'C' Woodstocks, that can die a quick and ugly death this way.)

Viktor

The HP-97, 91, 92 printers will instantly be destroyed if printing is attempted without a battery pack installed (or some other means to achieve proper electrical conditions) The card readers may not suffer as catostrophic damage but it will not be good for their operation.

Hmmm, what is the nature of the damage to the printer? I'm asking because I don't think I ever tried doing this (nor do I plan to, for all the obvious reasons); in fact, I recall only one time when I ignorantly attempted to operate an HP-97 without a battery pack many years ago, but I learned quickly that it isn't a good idea.

The HP-97 service manual, however, does state on page 2-5, that "with batteries removed, the calculator will not be damaged by connecting the ac adapter/recharger to the input terminals; however, it will not operate correctly until the batteries have been reinstalled."

Viktor

The nature of the damage is the printer motor gets too much juice and the gears on the drive mechanism (nylon) get stripped and are virtually irreplacable outside scavanging from another HP calc.

This only occurs if you attempt to print while no battery is present and I suppose it may not occur every time but I would hate to do a statistical study....

Gotcha, so the problem is not electronic in nature. This may also explain the relatively frequent reports I heard about broken nylon gears in Topcats.

Viktor

The yellowish gear may indeed have its teeth stripped by running it on the AC power supply only. However, the gear itself does decay over time. I've got a few 97's and they all have spur gears that are very brittle and starting to fall apart. So I think that it's both a nylon decay problem and a motor force problem. I'm very actively looking for a source of replacement gears. If anyone can help, I believe the specs are as follows:

24 pitch - 32 teeth total (about 3/8" diameter) - 3/32" face

3/32" bore

1/4" hub diameter - 3/32" hub projection

A spur gear with the above specs made from Delrin would be ideal.

Just checking Katie;
Would that outer diameter be 1-3/8"?

Glynn,

Nope. 3/8" is approximately correct. 32 teeth at 24 pitch is all you really need to know to determine the diamter of the gear.