tty and video displays

Jules Richardson jules.richardson99 at
Mon Dec 21 18:11:44 CST 2020

On 12/14/20 10:06 PM, Brent Hilpert via cctalk wrote:
> 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.


Just a heads-up, I finally got around to hooking it up - and it works just 
fine on -5V. I'm not inclined to try -12V just in case it cooks, but I 
suppose it's possible that it just needs some -ve voltage "more than x" and 
so -12V is perfectly acceptable, too. Or maybe I just got lucky and this IC 
is happy on -5V where some might not be.

I'm pretty happy that it's alive, anyway. I need to figure out what's going 
on with the spacebar (it currently doesn't sit level), but time to figure 
out some frankenproject for it!



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