On Sat, 7 Feb 2015, Brent Hilpert wrote: I checked 4 of the F5C-2 parts at random, and measured ~95k-96k between pin 1 and pin 14 (vcc) and infinite resistance (or at least off the scale on my Fluke DMM) between pin 1 and pin 7 (gnd). I guess that means they do indeed have some sort of internal pull-up resistor, but it certainly isn't much of one. OTOH, that makes sense since a larger value pull-up would limit current draw if you ground pin 1 to disable the oscillator. This does make me wonder even more what may have gone wrong in Noel's oscillator. I am familiar with some of these type of oscillators (and crystals) growing tin whiskers inside their cans, and I'm really starting to wonder if that's what caused that oscillator to fail. That makes sense. I'm almost 100% certain these parts did indeed come from an auction of a company that designed ASIC parts for modems (POTS, leased line, and ISDN) that closed one of their R&D labs in the 90s. I know for sure I still have some prototype 9600 and maybe even some 14400 modems that came along with the parts cabinets I bought.