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During last months I have collected some "scrap". I have four HP-41C calculators. One of them works just fine. I can´t turn on the other three. I have tried to swap the CPUs. The result is that the working CPU is ok in any case and the other three don´t work anywhere. So it is clear that the problem is the CPU, not contacts or displays. Any ideas?. May be there is a capacitor or something that fails in this model.
Sorry for my bad english, I hope you understand me.

Thanks in advance

Hi, why you don't try to exchange the memory ICs from one to another?
Best regards


I've seen several malfunctional HP-41 CPU boards.

In most cases so far there were one or more defective memory chips,

in two or three cases a bad ROM chip.

Remarkable is that it always was ROM 1,

or in other words, the second ROM chip.

Too bad one of the boards with a bad ROM chip is a CX:-(

Best Regards


Clean the circuit board very thoroughly with 91%+ isopropyl alcohol. Very often several of the chips were hand soldered down and the old solder flux residue causes problems.