What resolution are you trying to display ? What RamDAC is on the adapter ?
according to the datasheet you can get 16mil color but only at 640x480 mode and with the AT&T DAC, and still cannot get more than 256 color at 1024x768 with the 1Mb or more ram.
also says: Requires a Sierra HiColor DAC to use 32k or 64k color at 640x400 or 800x600 otherwise you are stuck at 256 color for 640, 800 and 1024 modes....
Datasheet also mentions it also depends on the BIOS on the adapter...

That compaq does not have a RAMDAC capable of 15/16 and/or 24bit modes, you are stuck with 256 colors regardless of driver. It should be possible to change the RAMDAC but it is soldered and perhaps the (video)BIOS itself cares that it is the right kind too...

I would like to run 16bit color if possible. From memory, I "think" the Prolinea 4/66 was capable of running 16 bit color. I have a 4/33. So there may be a difference there. If it just isn't possible it's not a big deal, but it would be nice. I actually e-mailed Microlabs and they responded, they sent me drivers for Windows 3.1 and NT 4.0. I could try the NT 4.0 driver, but at this point I'm not too optimistic. It's ok though, the machine is all fixed and running! I really appreciate everyone's help Horun, Tildo, thanks so much!

douglasfir wrote on 2024-02-11, 03:36:

I would like to run 16bit color if possible. From memory, I "think" the Prolinea 4/66 was capable of running 16 bit color. I have a 4/33. So there may be a difference there. If it just isn't possible it's not a big deal, but it would be nice. I actually e-mailed Microlabs and they responded, they sent me drivers for Windows 3.1 and NT 4.0. I could try the NT 4.0 driver, but at this point I'm not too optimistic. It's ok though, the machine is all fixed and running! I really appreciate everyone's help Horun, Tildo, thanks so much!

Make a picture of the RAMDAC sitting on the mainboard, and we can tell you more.

the RAMDAC is a Tseng labs tc6167.

douglasfir wrote on 2024-02-12, 18:20:

the RAMDAC is a Tseng labs tc6167.

That is not a picture.
Tseng labs tc6167 most likely is main ET4000/W32i chip, NOT the RAMDAC, there are no RAMDACs from Tseng as far as I know.

In the Compaqs in the line I have had access to all had a MUSIC branded RAMDAC, a PLCC44 chip near the VGA connector.

Here is a photo of the RAMDAC guys...

Yeah, this is 256 colors only DAC which also integrates a PLL to generate pixel etc. clocks so you cannot easily replace it with something else either.

Thanks so much Tildo, at least I know now! 😀

douglasfir wrote on 2024-02-13, 18:46:

Here is a photo of the RAMDAC guys... […]
Show full quote

Here is a photo of the RAMDAC guys...

Yes, only 256 colours.

Oh... i have repair a Prolinea 4/66 with a fault.
Line jitter

Internal PLL of GEN-DAC is bad.

I have no MU9C9760V spare.
I have placed MU9C9910V (i have ripped a dead board with this GEN-DAC ) into "Hudson"-Board (I called this board, because this board has cartoon "4-6-4 /2C2 steam locomotive" )
Compare with two datasheet: 9910 is register & pin compatible to 9760.... it looks good.

GEN-DAC swap -> Pictures is now fine

But, it is a big surprise

15/16/24bit color works on compaq prolinea4/66 board.
(checked with VESA BIOS extension tester aka VBETEST )