Mine finally died so I've got to open it up.  Looking over the schematics it looks like the monitor supplies isolated +5 VDC to the video card to drive the optoisolators.
The manual shows for the monochrome....
 
1 GND
2 +5 (out)
7 Video
8 Hsync
9 Vsync
 
And the video card schematic shows...
 
1 GND
2 External Power
3 IRED
4 IGREEN
5 IBLUE
6 GND
7 VIDEO
8 HSYNC
9 VSYNC
 
 
Page 7-11 of the 9100 service manual shows MJUMP or CJUMP to feed the ISO-PWR supply line which power the opto isolators.
 
I assume CJUMP is Color JUMPER?
 
So this leads to 2 questions.
 
Must the monochrome be optoisolated & power the Video card with +5VDC or can I use the CJUMP & run a monochrome monitor?
 
What is Intensity voltage level/range normally on a monitor?  (I'd like to use a non Fluke monitor)
 
Thanks,
Kev
 

3.8) CGA - TTL

(15.75 KHz - 320x200 or 640x200) DB-9 pin:

 1 GND                    6 Intensity
 2 Unused	          7 Unused
 3 RED Video              8 H Sync TTL Positive
 4 GREEN Video            9 V Sync TTL Positive
 5 BLUE Video

3.9) Monochrome - TTL

(18.43 KHz - 720x350) DB-9 pin:

 1 GND                    6 Intensity
 2 Unused	          7 Video
 3 Unused                 8 H Sync TTL Positive
 4 Unused                 9 V Sync TTL Negative
 5 Unused