The most likely cause of the problem is that the cable or monitor being
used does not ground pin 4. This is required for the built-in video
circuitry to identify a monitor as an AppleColor High-Resolution RGB
Monitor or equivalent. If none of the Monitor ID pins are grounded, the
built-in video assumes no monitor is attached.
The following portion of text from the Macintosh IIci Technical Tour
stack should clarify why the internal video circuitry of the Macintosh
IIci behaves differently than the Macintosh II High-Resolution Video Card.
Here is the text:
The Macintosh IIci has the equivalent of a video card built into the main
logic board. This means that Macintosh IIci owners do not have to
purchase a separate video card to use an Apple monitor with the unit.
This also means that all three NuBus slots remain available for other
NuBus cards. Other video cards can be added to any one of the three NuBus
slots.
The built-in video circuitry supports the following monitors:
Apple High-Resolution Monochrome (@ 2, 4, 16, and 256 colors/grays)
AppleColor High-Resolution RGB (@ 2, 4, 16, and 256 colors/grays)
Apple Macintosh Portrait Display (@ 2, 4, and 16 colors/grays)
The pinouts for this port are as follows:
01 RED.GND Red Video Ground
02 RED.VID Red Video
03 CSYNC Composite Sync.
04 MON.ID1 Monitor ID, Bit 1
05 GRN.VID Green Video
06 GRN.GND Green Video Ground
07 MON.ID2 Monitor ID, Bit 2
08 nc (No Connection)
09 BLU.VID Blue Video
10 MON.ID3 Monitor ID, Bit 3
11 C&VSYNC.GND CSYNC & VSYNC Ground
12 VSYNC Vertical Sync.
13 BLU.GND Blue Ground
14 HSYNC.GND HSYNC Ground
15 HSYNC Horizontal Sync.
Shell CHASSIS.GND Chassis Ground
The pin requirements for making a cable for a Macintosh IIci to a Portrait
display are as follows:
DB-15 (Macintosh IIci) DB-25 (Portrait)
---------------------- ---------------
03 05
07 08
08 04
10 03
11 07,10
12 02
14 01
15 06
Shell Shell
There is an issue with some third-party video cables and third-party video
cable extenders. Some of those cables included just the necessary pins to
support the Apple High-Resolution Monochrome Monitor or the AppleColor
High-Resolution RGB Monitor with the Macintosh II High-Resolution Video
Card.
One problem with some of these cables is that pins 4, 7, and 10 are used
to identify the monitor that is connected. With the Macintosh II
High-Resolution Video Card, pin 4 was a ground line, but pins 7 and 10
were not used. With the color and monochrome monitors, the problem is
that some of those cables leave out pin 4, and tie to another ground. In
these cases, the built-in video fails to detect and identify the monitor.
This causes built-in video to be disabled. However, if the cable or cable
extender connects pin 4, the cable should allow the Macintosh IIci to
correctly identify the Apple High-Resolution Monochrome and the AppleColor
High-Resolution RGB Monitors. Most cables support the other signals
required for these two monitors.
A second problem is that, given the fact that the new Macintosh
IIci-to-Portrait Display cable has a 15-pin connector on one end, it can
be connected to third-party video cable extenders. However, all of the
lines that were unused by the Macintosh II High-Resolution Video Card are
now used to support the Macintosh Portrait Display. As a result, any
video cable extender that does not include these lines will not support
the Portrait Display. In this case, the Macintosh IIci may not be able to
identify the monitor because lines 7 and 10 probably will not be connected
and the required video signal lines will not be there either.
SPECIAL NOTE: To meet FCC part 15 requirements, the Apple-supplied cables
have to be used.