hp35 Dead


I bought recently a hp35 wihtout battery pack and charger , I made the battery pack and I installed but the machine does not work .
I revised the switch in the charger conector and its OK but the machine its totaly dead .

Any sugestions?

Thank YOU.


Have you checked/wiggled/cleaned the ON/OFF switch.

These get intermittent as they get used. On my 1973 model, I have to switch it on and off a few times to get it going reliably.


Hi Victor

I acquired an HP35 a short while ago with the same problem. It was because the finger spring connectors (which run across the very bottom of the calculator) between the keypad and main PCB were not maintaining a reliable connection. The fix was to remove the main PCB and insert a flat blade jewellers screwdriver between the tines on each contact and twist gently and (very, very) carefully to spread the tines just slightly, thereby ensuring a better interference contact with the bosses on the main PCB. I scrubbed each contact and boss with an alcohol soaked toothpick and put the machine back together and it has worked perfectly ever since.

Good luck getting your 35 running,

Best regards, Hal


there may be however, a dead circuit.

Check this posting on an HP45 restoration and you will see the mechanism and why the switch might not work:


Hope this helps, geoff

Edited: 10 May 2008, 3:47 p.m.


I suppose that the problem is in the switching power supply because I dont have the VSS (+6V) Vgg(-12V) and VCC (+8,2V) even I have the 4v from the batteries on the Logic PCB .
Do You know how work this power supply?
Thanks a Lot.



Buenas dias, Victor,

IF you tried to measure the output voltages at the charger with NO calculator connected, and did not get anything, THEN I'd recommend you try to get a new charger. They don't cost a fortune and are frequently offered.

ELSE the postings above apply.

HTH, Walter


I would sell it on the unmentionable auction website as a "For repair" listing. Then snap one up.

Good luck!



I would sell it on the unmentionable auction website as a "For repair" listing. Then snap one up.

No, no, no! You describe it as "last time I used it, it was still working, but now I can't find the charger any more and therfore must sell it as untested". This phrasing is very popular among people who sell three or four calculators every week...

But seriously: I would try to get a second one (they are really not expensive compared to other models) and switch components/circuit boards between the two until the defective part can be identified.

Greetings, Max

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