Bad HP41 Time module


I have a bad HP41 time module, can see the catalog of functions, but when I execute the CLOCK function (or SHIFT ON), the calculator powers off! Is not the calculator, I have tried it in an HP41C and HP41CV with same results.
It seems that the quartz crystal of the time module is faulty. At which frequency is rated the quartz crystal of the time module? According to Appendix F of HP41CX Volume 2 manual the frequency is 10240 Hz. is this right? Any help would be apreciated.



New Batteries !!! :-)


Thanks, but I´ve already tried this with no solution. SHIFT ON powers off the calculator


Hi, Gonzalo;

if you try TIME instead of CLOCK, does it happen the same? Let us know.

Success and best regards.

Luiz (Brazil)


TIME always shows 12:00:00 AM It seems to me that the crystal quarts is broken, because I can see the catalog of functions but time doesn´t run


It's unlikely to be the quartz crystal itself, because those things are so simple - just a piece of rock, shaved to size, with two wires attached, basically. It's more lkely to be some other part of the oscillator circuit.


--- Les



... a cold, broken solder. I agree with the fact that a quartz X-tal is somehow hard to be a deffective componnet, but in this case, if TIME returns 12:00:00 everytime, it tells me that the clock is not ticking. If the crystal is disconnected, a tinny little bit of well placed solder might solve the problem. In time: is the crystal of the time module a discrete component or would it be integrated, I mean, in the same package of the rest of the module's circuit? Anyone with a picture?


Luiz (Brazil)


The frequency is 32768 Hz. The manual mentions the frequency after the prescaler, the design specification of the time module states 32kHz, and I measured the clock of a HP-41CX fullnut to be sure.


Thanks for the responses. The crystal is a discrete component, with a parallel attached resistor. Will measure the frequency and try to retouch the soldering points.


The crystal is 32768 KHz. This is a common part and fairly easy to find. I have seen a couple of 41CX's with bad timers. The problem was the 22 megohm resistor.


The crystal is good, I have tested it with a oscilloscope. The resistor is 30Meg. As soon as I power on the calculator, a sine wave appears in the crystal, but the time doesn´t advance. I will have to get a small microswitch (like the ones found in HP48GX memory cards) and mount it in the time module. I power on the calculator with the switch off (no resistor attached in the crystal), then I turn the switch on (now the resistor is in parallel with the crystal) and now the time advance and it seems the module function correctly. A strange behaviour, but at least the module works in this manner and holds the time even with the calculator powered off.

Thanks for all your responses


I would try some different values for that resistor (10/15/22 meg). Mayby the crystal has aged some and needs a little extra drive.

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