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Full Version: adult supervision for me & my 35
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i found a 35 in a thrift shop yesterday after work. it works fine on the charger but it does not work off a good battery. it also will not charge a battery using a known good a.c. adapter. i took it apart and saw no loose wires or leaky battery mess crossing any contacts, nothing obviously fried.
i know nothing about electronics but i may be able to ask a neighbor to test something if i knew what to test and what it should read.
any ideas?

I have seen this happen lots of times. It is usually caused by hidden corrosion on the battery contacts in the calculator or similar contact related problems. The contacts touch the battery pack via their curved top EDGES, not the little bump on the end of the contacts. Sand the edges with very find sandpaper. You can check if this is the problem first by conencting a known good battery pack to the contacts with clip leads.

The only battery-related circuitry in the HP35 (or in other classics) are connections between the battery contacts and 2 pins on the charger connector. And a spring contact in the bottom case that connects the outside 2 pins of the charger connector together when the charger is not plugged in, and thus connects the battery to the rest of the calculator.
So, with the back case off, check for continuity (very low resistance) between the rear (display-end) -ve battery contact and the middle pin on the charger connector, and between the front battery contact and the outer charger connector pin that's not on the side of the machine where the on/off switch is (this is the clearest way I can think of to describe it). If either connection is open,
remove the logic PCB (it just pulls off the pins, but handle it by the edges to avoid static damage), unscrew the chassis plate, and check/replace the wiring on the back of the chassis.
If the connections check out fine, make sure the battery contacts really are clean. The connection to the battery pack is made via the 'sides' of the contacts and small
amounts of corrosion/dirt can cause problems

first off i scotch brited the battery tabs and put a little more sproing in the spring contact, then i held it together and it works. next time i'll clean first and ask later. you guys are the greatest!