Please help - misbehavin' HP-71b

From: Tony Duell <>
Date: Wed Aug 6 17:02:05 2003

> I hope someone can quickly let me know the answer.
> Is it normal for an HP-71b that has been without batteries or use for a
> while to refuse to start up once you put batteries in _until_ the PSU is
> plugged-in? Once it's been started with the PSU plugged-in, it works

No it's not normal...

The PSU is just an 8V mains transformer with poor regulation. In the
HP71, the output of that transformer is rectified and smoothed, and then
fed to the same (discrete component) regulator circuit as the batteries
(no attempt is made to charge the batteries, BTW).

The only thing I can think of is that the PSU probably gives a higher
input voltage to the regulator than the batteries do. Why that should
help it start up I don't know (according to the schematics I have,
everything runs off the output of the regulator).

Is this problem repeatable? If you pull the batteries and leave it
overnight (and, in fact, to ensure the darn thing is fully discharged,
short the outside 2 pins of the card reader connector with the batteries
and PSU removed), and then put the batteries in, does it still refuse to

I assume you have no modules in the machine.

Received on Wed Aug 06 2003 - 17:02:05 BST

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