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HP Forum Archive 15

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HP-41C non working
Message #1 Posted by Pelopi on 14 June 2005, 4:46 p.m.

During last months I have collected some "scrap". I have four HP-41C calculators. One of them works just fine. I canīt 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 donīt 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

      
Re: HP-41C non working
Message #2 Posted by Artur - Brasil on 14 June 2005, 5:24 p.m.,
in response to message #1 by Pelopi

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

            
Re: HP-41C non working
Message #3 Posted by Raymond Del Tondo on 14 June 2005, 5:46 p.m.,
in response to message #2 by Artur - Brasil

Hi,

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

Raymond

      
Re: HP-41C non working
Message #4 Posted by David Smith on 15 June 2005, 4:57 p.m.,
in response to message #1 by Pelopi

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.


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