SGI SN-921 dial box (978-0804) (was Re: IBM 6094-010 "Dials" protocol?)

[Ethan Dicks]

On Sun, Mar 25, 2018 at 6:09 PM, Ethan Dicks <ethan.dicks at gmail.com> wrote:
>> SN-921 (2.1mm barrel jack for +5V)
>>   https://upload.wikimedia.org/wikipedia/commons/7/74/Sgi_dialbox_sn-921_front.jpg
>
> http://yehar.com/blog/?p=3471
>
> The (Seiko?) SN-921 can apparently be powered via DE9 or the 2.1mm
> jack next to it...
>
> 1. GND
> 2. SERIAL OUTPUT (±9 V)
> 3. SERIAL INPUT
> 4. POWER IN +5 V
> 5. POWER IN +5 V
> 6. NC
> 7. NC
> 8. GND
> 9. NC

Now that I've poked around in the innards, I can say that this pinout
has a slight mistake in it.  It should be:

1. GND
2. SERIAL OUTPUT (±9 V)
3. SERIAL INPUT
4. POWER IN +5 V
5. POWER IN +5 V
6. NC
7. GND
8. NC
9. NC

There are mentions here and there about how to hook up this dial box
using the +5V power jack and DE9 pins 2, 3, and 7.  I can confirm from
direct examination that pin 7 is a ground and 8 is NC on the PCB (and
that 4 and 5 are connected directly to the center pin of the 2.1mm
power jack).

-ethan