|Re: how to accelerate an HP 41C???|
Message #3 Posted by Peter on 25 Apr 2005, 10:28 a.m.,
in response to message #2 by Garth Wilson
Though compared to the real Giants here I'm an amateur, yet let me try to offer some info, until they come in and fix the wrong part.
If you have a Fullnut (no rounded corners in the display) the necessary change is relativly easy to do. It involves adding a second capacitor and a switch to the timing capacitor (150pf, in parallel to coil, on various places depending on the board layout).
I;ve taken pictures of about 5 board layouts so far and marked the 150pf, yet have not found a place to publsish them (I checked out Dave's comments yet he asks, rightfully so, for pictures not too large and I had not time to reduce the size of my pictures yet. lazy bug I am and then this other thing, might be called "work" gets in the way every so often. Very annoying...) But I can email them to you if you are interested.
One needs the switch to be able to move back to normal speed to use the card reader or cassette drive. The wand on the other hand works just fine.
I have a set up at home that uses a variable capacitor and a testprogram (I think it is from a PPC or HPCC journal) to find the maximum speed a certain calc is still working perfectly. Older boards sometimes only work well until about 160% speed, while newer boards (especially Halvenuts, more to them later) work up to 270% or even more.
There is a service manual available at the DVD of TOS (please search this site for this expression to understand it). It has most/all layouts to locate the 150 pf for the halvenuts. Unfortunately it does not have the shematics for the Halvenuts.
As for halvenuts, they generally can tolerate higher speedus, yet it is a bit more tricky to perform, as the cap is a SMD and (I believe) even for the C one would have to desolder the "bridge" (I've actually never seen the pcb of a 41 C halvenut, only CV and CX), which is a delicate business in and by itself. The cap in question can be found right under the board (thanks to a description by Tony Duell...)
That's about all that I know. As for doing it - where r you located?