HP15c runs slow

[Katie Wasserman]

I agree with Jlouis, start by removing the batteries and shorting the battery contact together briefly to see if that helps. If not, open the calculator and inspect the inductor and capacitor that form the oscillator (it's an LC circuit not an RC circuit, at least on the US versions, and I'm pretty sure on all versions from that time period). Just reflow the solder on those components.

If that still doesn't work try replacing the capacitor with a 180pf ceramic one or something close to that value. The inductor is around 180 uH, BTW.

FYI using a smaller value inductor and/or capacitor you can speed up the calculator by a factor of 2 or more. This comes at the expense of higher current drain of course.