HP41 Fault, Any Ideas?


My HP41CX has recently developed a series of faults, I first noticed that the auto-off function was less than one minute, then sometimes when I switched on all the character segments 'lit', also sometime a high pitched whistle is heard when any key is depressed.

Does anyone know what causes these faults and whether they are terminal?




Correction to my previous post..

The calc in question is a 41CV (not a CX)

BTW it wont switch on at all now!



I had a CV that exhibited some rather strange faults, including refusal to power up at times, turning off at odd times, strange display stuff...

In my case it was the links between the display pcb and the keyboard pcb. These are soldered. SOme of the connections had fractured, and others had lifted the track on the pcb.

Have a close look at these, especially if pressing harder on the keys, or flexing the case slightly makes the problem worse.


Over the years I have encountered some problems ... I have rarely had high-pitched noises, ande they somehow seemed associated with using Synthetic Programming. There is no harm in this.

The lock-up (won't turn on can happen when the CMOS processor locks up. Synthetic Programming or untimely or improper removal of modules can cause this also. Removal of the battery overnight usually clears this. If 48 hours of no batteries does not fix it, then it's not the CMOS-lock-up that caused the problem.

The calculator CMOS uses a resistor-capacitor (RC) combination to set the timing clock for the CMOS processor. A "speed-up" can be done by changing the capacitor. Is your clock (not time module) running fast? Execute BEEP and see if it sounds much shorter in duration and much higher in pitch. The auto-off feature is nominally 10 minutes on an unmodified calculator. A double speed clock will result in auto-off in half the time (5 minutes).


Do you have any ROM modules plugged in? I've seen all the symptoms you describe (especially the high-pitched noise) if a module is not plugged in all the way. The connections can become a bit worn from use, and although the module LOOKS like it's inserted properly, it may not be making full contact. Try removing the modules and see if the problem goes away. If so, try each module one at a time in each port and see if that makes a difference. Sometimes, wiggling the module a little as it's seated helps it make good contact. (Of course, turn the calculator off each time before you insert or remove a module.)

Even after removing the modules, you may have to reset the calculator a few times (by pressing the BACKSPACE and ON buttons) to get it back to normal. It might even be necessary to remove the batteries overnight (although I've never yet had one lock up THAT badly). Sometimes it takes several reset attempts before I get the "MEMORY LOST" message.

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