On 2020-Dec-14, at 7:57 AM, Jules Richardson wrote: > On 12/14/20 4:41 AM, Brent Hilpert via cctalk wrote: >> >> Yes. Coincidentally I've just been refurbishing one - a Teleray 3931. >> It's an ASCII/APL terminal, overstriking was included for the APL mode. >> http://madrona.ca/e/teleray3931/index.html > > Holy cow, I have that keyboard. ... > (It's definitely -12V, not -5V? I'm just thinking that the -12V noted on your > schematic is quite close the the 15V rating on the cap - although that could > explain why my later setup got caps rated to 35V, too)
I don't remember whether I traced it or measured it, but I'm fairy confident, Vgg = -12 is pretty common for GI MOS ICs. I'll try to remember to double-check it when I have the unit opened again. I have some other orphan keyboard of the period, don't recall which scanner IC it uses, but it has the similar +Vcc/-Vgg requirement. I made up a little negative supply with a 7660 charge pump and tacked it onto the keyboard PCB so the keyboard now only needs +5 externally.
