21 Oct
2011
21 Oct
'11
9:51 a.m.
On Thu, 20 Oct 2011 20:18:06 +0100 (BST), ard at p850ug1.demon.co.uk (Tony
Duell) wrote:
There is a *much* easier way to do it, which doesn't mutilate the pack
anywhere as badly.
Cut through the strip of plastic which runs along the pack between the
batteries at one end, using e.g. a pair of side cutters or a scalpel.
The strip will now flex out of the way sufficiently for you to be able
to prise the batteries out, one at a time. Then push the new batteries
in the same way. This operation doesn't weaken the pack mechanically to
any noticeable extent, it can be used just as before, and the batteries
can be replaced any number of times.
OTOH it is harder (not very) to get the cells out to charge them in a
normal charger.
Note that the contacts in the calculator are simply large rivets
soldered in to circuit board fingers. That solution is a bit of a
let-down IMO, as is using the battery as a load to reduce the voltage
from the charger, simply limiting the current with a whopping big
resistor. It could have been done a lot better, and not much more
expensively.
Everybody who had an HP-25 (just about everybody who didn't have a
TI-57) when I was at University learnt to do this.
/Jonas
years ago).
How hard is it to replace the batteries?
Very easy.
The battery pack clips into the bottom of the machine, you just slide
it
slightly forwards (towards the '0 key end' of the machine and lift
the
rear edge to get it out.
The battery pack contains 2 AA-size NICd cells connected in series,
normally by a double-spring thingy (that;s a highly techncial term,
of
course). The housing is made in 2 parts which were glued together.
You
cna crack the glued joint, take it apart, and fit new cells.
But actually, I don't recomend doing that. It's better to cut away
the
pack housing ad the front end, where the cells touch the contacts in
the
calculator. Then silde out the old cells and slide in the new ones --
taking care of the polarity (since HP calculators were designed for
use
with their own battery packs only, which only fitted the right way
round,
there is no reverse-polarity protection. The cells will be held in
place
when the pack is clipped into the calculator, and you can remove the
cells easiy for charging in a normal charger, thus avoiding possible
damage to -C models.