HP-41CX speed down



#4

Hello
I recently bought a near mint HP-41CX. The former owner had it tuned for high speed, but after about 8 years in his drawer, the thing only works sometimes. When I try turning it on, the display sometimes shows "12:00:00 AM", as if it has just been performing a reset. Nudging the case a little, I sometimes can retain the calculator alive in a couple of minutes. How can I put it back to its original speed and woring state? How do I open it? I noticed that the rubber feet has been replaces with some kind of unoriginal pisces of foam-rubber, so I guess that I can find the screws under theese... Is there a web-page dedicated to HP-41 hardware, as in the case of the HP-48 opening?

Thank you from a newly started HP calculator collector, with only 6 HP's yet in stock!
Johnny!


#5

This, yet again, sounds like bad internal connections in an HP41. They suffer from this problem....
And nothing more serious, hopefully. Yes, the fixing screws are under the feet. Take off the feet and undo the screws (Oh yes, remove the battery pack and any modules first).
Early design machines have a separate logic board at the front end of the case, later machines (the 'halfnuts') have everything on one PCB.
See the other thread here on HP41 repairs. You'll see that the battery contacts and
module ports are actually a flexible PCB wrapped round a plastic support. Part of this flexible PCB is pressed against pads on the keyboard PCB. Clean the contacts on both sections with propan-2-ol and squeeze the foam under the flexible PCB to improve the contact.
If yours is the older construction, lift off the logic PCB and the connector assembly under it, and clean the contacts there too. Take anti-static precautions when working inside the HP41 -- this is delicate CMOS circuitry.
Then put it all back together and try it out again.

#6

HI Johnny I also have a speed up hp 41cx.( not working correctly) Look in the articles forum for reparing a hp 41 cx. You can also look in the forum for april 2001 ( where i had a correspondance in this matter. stefan


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