tty and video displays

Jules Richardson jules.richardson99 at
Mon Dec 14 09:57:26 CST 2020

On 12/14/20 4:41 AM, Brent Hilpert via cctalk wrote:
> On 2020-Dec-14, at 1:26 AM, ben via cctalk wrote:
>> Often for data input one could use over strike characters for input. Not EQ might be = BS | Did any video display terminals
>> repeat the same effect?
> 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. I picked it up as surplus a few years ago 
from a place in Minneapolis and figured there was a very low probability of 
ever figuring out what machine it originally came from.

I didn't know the necessary voltages for it - I mean, the grounds and +5V 
are obvious, but I didn't know what it needed on pin 6. Given where I got 
it from, there's probably a fair chance that it's faulty (and encoders 
generally live a hard life), but I'll have to try powering it up now.

Just FYI if you're documenting things, mine has a very slightly different 
PCB to accommodate a pair of tantalum caps on the inputs, rather than the 
electrolytics on yours - caps are both rated 10uF, 35V. The encoder on mine 
is the same p/n but in a black plastic package rather than white ceramic 
(date code 7649). Sticker on the PCB underside says p/n 2129-009 and s/n 
720 097.

(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)



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