HP-75C battery repair


Hello HP lovers,

I am trying to restore a HP-75C S/N 2304... with a rather damaged battery compartment. I am a bit puzzled because it contains 3 contacts and, as far as I know, the corresponding battery pack 82001B only have 2 pads. Refering to the battery compartment on the picture http://www.hpmuseum.org/75int2b.jpg, I have the two left contacts (top=black wire, goes to VN on PCB i.e. ground; bottom=red wire, goes to VB on PCB) and an extra contact on the right side of the top ground (blue wire, goes to VA on PCB). A previous owner apparently has tried to cut it and to solder it to the top ground contact. Does anyone else have the same configuration? Is there a battery pack similar to the 82001B with 3 pads. I assume the third contact is designed to recharge the battery ... should I keep the makeshift jumper to the top ground contact? Any suggestion?

Kind regards.


I have a 75D. It has some extra features molded into the plastic in the battery compartment which I just realized are for a third battery contact. It would touch the negative battery pack terminal, if it had the same shape as the other contacts and was maybe a little longer. I have a 1988 Sanyo NiCad databook which includes a picture of an HP Classic battery pack in a chapter about multi-cell assemblies - it looks identical to the packs I have except that the contact openings in the molded plastic are a little shorter - they go about as far toward the middle but not so far toward the end - my packs are all 82001B, maybe the picture is 82001A. Anyway, the databook suggests that in some applications it is a good idea to have a separate contact to apply recharging current to the pack. I think they are talking about applications that can use either rechargable or regular batteries.

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