|Re: Triple speed 15C - after 22 years|
Message #10 Posted by Karl Schneider on 17 Oct 2009, 4:33 p.m.,
in response to message #1 by Lyuka
Nice work and photos!
I'd like to make a few comments:
1. Your modifications -- replacement of two capacitors and one inductor, plus addition of a parallel capacitor -- were more extensive than the simple parallel-inductor addition described in Ken Sumrall's writeup hosted by Eric Smith.
2. Was the purpose of lowering the oscillator capacitance values to achieve further increases in resonant frequency while maintaining an L/C ratio of the oscillator closer to its unmodified value? The better-matched L and C components would help to retain more energy-exchange capability and resulting magnitude of the oscillator voltage.
3. Was the bypass capacitor replaced with a higher-capacitance part in order to help compensate for the other changes?
4. Both of your HP-15C's are of the revised (1986-89) Voyager circuit design, with most or all of these parts atop the circuit board that allows easy replacement. The modifications you made appear not to be suited to the original (1981-85) circuit design:
5. Original-design Voyager units lack the same external connections for the bypass capacitor shown on the right side of the photos, as well as for the lower oscillator capacitor on the left side. Also, the oscillator capacitor is of a large "can" style residing in the cutaway of the circuit board, below the battery (shown on your older 1986 calculator). The oscillator inductor is very difficult to access, residing below the circuit board.
6. Your photos did not include one of the unmodified older (1986) calculator. I assume that its oscillator capacitor was can-style like those of the original design. (I have a 1985 unit that has the cutaway as well as the same type 1LM2-0001 CPU).
I based a speedup of my 1985 original-circuit HP-15C on Ken Sumrall's approach. At first, I simply connected a 22-mH inductor in parallel, to give a 3.3x increase in speed. However, the calculator later malfunctioned at healthy battery voltage, so I removed the extra inductor, which restored proper operation. Next time, I will install a 33-mH part for a 2.75x increase in speed.
Edited: 18 Oct 2009, 9:58 a.m.