hp41c overclocking

[GeorgeOfTheJungle]

Anyone who can point me the clock's RC in this hp41c pcb, or a link to the schematics, please?





Thank you,
Jorge.

[rprosperi]

Best overclock option for the 41 is to get an HP-41CL upgrade board (search for it, its trivial to find, both here on MoHPC and Google). 50 (yes, that's fifty) times faster, plus all the ROMs any reasonable person could want. And while very few of us here are truly reasonable, all are happy with the 41CL.

[GeorgeOfTheJungle]

(05-31-2014 05:00 PM)rprosperi Wrote:  Best overclock option for the 41 is to get an HP-41CL upgrade board (search for it, its trivial to find, both here on MoHPC and Google). 50 (yes, that's fifty) times faster, plus all the ROMs any reasonable person could want. And while very few of us here are truly reasonable, all are happy with the 41CL.

Yes, I've seen the CL, it's awesome, and I like it very much buuuut... what I want to do is to overclock my 41c :-). The function generator is on and ready, eager to inject a faster clock into the pin... what pin is it?

Could you please help me locate the schematics? I know they're somewhere in one of the several hp calculator fanboys'^W sites, but which, where, exactly? Google isn't being my friend... or I am being too clumsy.

Thank you!

[Massimo Gnerucci]

(05-31-2014 05:21 PM)GeorgeOfTheJungle Wrote:  Yes, I've seen the CL, it's awesome, and I like it very much buuuut... what I want to do is to overclock my 41c :-). The function generator is on and ready, eager to inject a faster clock into the pin... what pin is it?

Could you please help me locate the schematics? I know they're somewhere in one of the several hp calculator fanboys'^W sites, but which, where, exactly? Google isn't being my friend... or I am being too clumsy.

Thank you!

Given that nothing beats a 41CL...
Here we go: schematics (french text)
Old threads (1 and 2) about possible compatibility problems.

[GeorgeOfTheJungle]

(05-31-2014 06:09 PM)Massimo Gnerucci Wrote:  Given that nothing beats a 41CL...
Here we go: schematics (french text)
Old threads (1 and 2) about possible compatibility problems.

Grazie mille. La rivista francese è eccezionale. And I have found the service manual, in the end, it seems, it boils down to L1 and C4, CPU pins 9 & 10:

   

Does that sound right?

Ciao.

[pito]

The LC seems to be the right place. In my HP-25 it is 150uH and 330pF (0.718MHz).
The question is how far you can go, without to see system's instabilities. That becomes a "try and error" exercise then..

The LC resonant frequency:

F^2 = 25330 / (L*C)
F in MHz, L in uH, C in pF

Decreasing L and C will push the F higher. I would change L and C such I would maintain the constant L/C ratio, though.
For example by the halving both L and C you double the frequency.

The lower you go with L and C the worse Quality (Q) of the resonant circuit you get, therefore the oscillator on the chip may refuse to oscillate.
If you are adventurous enough you may try to use a crystal instead of the LC. For example ~1.8 MHz, 2MHz and ~3.6MHz crystals are available. The crystal has much higher Q than the LC - that may help the oscillator to work more reliably. Also wiring a ~1M resistor in parallel to the crystal may help.

PS: your L=82uH and C=150pF (HP41C Service manual July 1979)
F= 1.44MHz
Thus to ~double the frequency (for example) you have to go with L=39uH and C=82pF..

PS1: do it at your own risk, no warranties of any kind..

[Dave Frederickson]

When I installed the speed-up in my 41 in the 80's the only component I changed was the cap. There are numerous articles on this in the PPC Journals.
If you're clever you can install a small slide switch inside the battery compartment. The switch is in series with a cap and the two are in parallel with the cap mounted on the PCB. The cap on the PCB is the smaller valued part and the parallel combination equals the value of the original cap. This allows you to switch between 1X and ~2X speeds.

Dave