Some of my other finds in St. louis

From: Keys <>
Date: Wed Sep 24 18:29:37 2003

Thanks for the great tips.
----- Original Message -----
From: "Tony Duell" <>
To: <>
Sent: Wednesday, September 24, 2003 3:58 PM
Subject: Re: Some of my other finds in St. louis

> >
> > Got the following items various thrifts in St. Louis:
> >
> > HP 33C calculator with case and charger for $5
> Nice, but a word of warning.
> DO NOT connect the charger to that machine unless there's a known-good
> battery pack in it. The battery pack acts as a shunt regulator for the
> PSU, and if it's missing/open circuit, the PSU rail will rise to about
> 17V.
> If the calculator is turned on when this happens, not too much damage is
> done, because the calculator draws enough current to pull the voltage
> down. But if the calcualtor is turned off, and it's a -C (continuous
> memory) model as here, the CMOS RAM chip gets the full 17V, and promptly
> expires. It's HP custom, so you then have big problems.
> HP sold some things called 'reserve power packs' which were battery
> holders without the rest of the calculator. You plugged the standard AC
> adapter (charger) into that, and put the battery pack in. The idea was to
> charger one pack while using another in the calculator, so you always had
> a fully chargeed battery even if you used the calculator away from mains
> power all the time.
> HP enthusiasts have found that these reserve power packs are also useful
> for charging batteries with no risk to the calculator if the battery goes
> open-circuit (if the AC adapter is never connected to the calculator, the
> RAM can't get the overvoltage). Unfortunately for you, the reserve power
> pack for the Spice series (HP3xE, HP3xC) is by far the rarest one, to the
> extent that some say it never existed (it did, I have one).
> -tony
Received on Wed Sep 24 2003 - 18:29:37 BST

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