My Compaq Presario CDS 633 outputs color in Windows 3.1, but not in DOS.

How can I get color in DOS?

I have tried the MODE setting, but it did not change anything. ANSI.SYS also has a LOADHIGH line in CONFIG.SYS. Files of potential relevance are here: http://www.jacobspctuneup.tk/SE/RetroComputing/

A few notes:

  • The computer was a floor model, and the monitor was bought with the computer.

  • On the monitor connector, pins 9,12, and 15 are missing, and pin 11 is bent to the pin 12 position.

  • There is no hole for pin 9 on the VGA connector on the computer.

  • What kind of graphics adapter does that computer use? If you go into the Windows 3.1 settings, does it list the GDI driver in use?
    – Zoey Boles
    Apr 19 '16 at 23:51
  • Please do not down-vote without giving a reason. If you think this is a poor question then say why in a comment. Apr 19 '16 at 23:51
  • 1
    I didn't downvote, but you should add your config.sys code.
    – user3169
    Apr 20 '16 at 0:45
  • 3
    What DOS only programs have you tried that are not displaying in color? Apr 20 '16 at 6:11
  • 1
    Does your graphics card have some sort of DIP switchs available at the back of the computer? Apr 20 '16 at 6:14

My guess is that your VGA monitor is reporting itself as a mono monitor to the VGA card. This may be caused by the monitor being too modern for your Compaq: The VGA card expects the monitor to report its capabilities using three pins from the VGA connector, but modern monitors use I2C to report EDID information on those pins. If the impedance at some of these pins is too low or too high, they may be read as N/C or GND.

Quoting http://pinouts.ru/Video/Vga15_pinout.shtml

ID pins set-up

4    11   12
ID2  ID0  ID1

n/c  n/c  n/c   no monitor
n/c  n/c  GND   Mono monitor which does not support 1024x768
n/c  GND  n/c   Color monitor which does not support 1024x768
GND  GND  n/c   Color monitor which supports 1024x768

GND means connected to ground
n/c means that the pin is not connected anywhere

If this is happening, the VGA BIOS will reprogram the internal palette to show gray shades instead of colors. To find out if this is so, you can test this:

Without starting Windows (that is, in "pure" DOS mode), execute debug


And enter these commands at the debug command prompt (a dash):

-o 3c7,0

This is to select DAC palette registers for read. Now, repeat the following command three times to get the R,G and B information for each palette entry.

-i 3c9

After entering the i command, debug will return the byte at that I/O port address, as in this example.

-i 3c9
-i 3c9
-i 3c9

My first palette entry is therefore RGB(0,0,0). Do it a second time

-i 3c9
-i 3c9
-i 3c9

My second palette entry is RGB(0,0,2A), which gives me a dark blue.

If you continue doing this, you will get the RGB values associated to each palette entry. A VGA card programmed with a grayscale palette will show identical values in R,G and B for each non-black color. For example, the second palette entry may show like this in a B/W setup:

-i 3c9
-i 3c9
-i 3c9

Which is roughly the grayscale shade equivalent to the original dark blue color.

To quit debug, just enter q at the debug command prompt.

If with this test you conclude that your monitor is reporting itself as a B/W monitor to your VGA, a solution would be to take a VGA extension cable and wire it so pins 4 and 11 at the VGA card side go to GND, and pin 12 is left unconnected. On the VGA monitor side, these pins may be unconnected.

  • Yes, this seems to be the problem. Any specific advice for the specific connector config being used? (See updated answer.) Apr 21 '16 at 21:59
  • 4
    Unbent the pin on your VGA cord. It's a classic fault with the DE-15 connector, that some pins become bent due to careless operation. Hopefully, you won't need any adapter. Apr 21 '16 at 23:45
  • Yay! After 22 years without color, it finally works! Bonus question: Why would the computer store purposely bend pin 11 into the pin 12 position? The way it specifically was in the pin 12 position, it couldn't have happened accidentally. Apr 22 '16 at 17:49
  • 4
    Are you sure? It's not the first time I see a pin bent so that it goes horizontal and then, vertical in the place of another missing pin. Someone once plugged that VGA cord with too much determination :D Apr 22 '16 at 21:03
  • 2
    @user4901968 it could have just been bent in that general direction, and then when the plug was forced into a port, the port did the rest of the job of bending it into alignment. A connector without all of the pins aligned on sockets wouldn't be able to plug in at all.
    – hobbs
    Sep 25 '16 at 7:05

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