tty and video displays

Brent Hilpert bhilpert at
Mon Dec 14 22:06:25 CST 2020

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.
> 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.

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