Dead HP35?

Hi there,
today I found a HP35 with Charger on a fleamarket. Got it for 2.5 Euros (appr. 2.5$).
And I did'n look into the battery compartment before I paid for the calculator.
The calc has the Ser.No 1302S 75403 and the batterie are numbered 1420-0272. I think this means that both, the calculator and the batteries are about 30 years old.

They looked this way, a huge amount of crystals from the electrolytic and green and blue debris from the junction of electrolytic and copper...
The liquid managed to reach the supply-unit's plug in the calculator.
Testing with a regulated power supply, the calculator doesn't work :-(
I didn't peel off the back label yet, are there any experiences that the calculator can be get back to life?



If the fault is bad connections, corroded wiring, or a problem with the discrete components in the power converter circuit, it can be fixed. If the problem is a dead IC, well, then you need to find another machine to raid parts from as all the ICs in an HP35 are custom.
So it might well be able to be repaired. It's certainly worth peeling off the label, taking the case apart and having a look. And if everything looks alright, then power it up from the bench supply and test at least the power voltages on the testpoints.


Don't peel off the full label. You just need to carefully peel back the top corners of the label (around 1/2 inch).


Hi David,
can you tell me the coordinates of the two hidden screws?
Then I will drill holes to get them out.
It seems to be a better way to me than peeling off the thin
aluminium plate.



Hi Tony,
Thank you for your answer.
I hope it will be not too bad.....



You rub around the upper corner of the labels with your finger and find where the screws are. If I remember right, the screw holes are mayby around 5/8 inch in from the edges of the label and around 3/8 inches down.


Hi David,
thank you, Iwill try it.


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