Hexedit analysis of the ROM could be helpful.

TheMobRules wrote on 2021-07-25, 20:14:

By the looks of it I assumed it's probably a monochrome adapter with a character ROM

I wouldn't be surprised if it is a combo MDA/Hercules/CGA card. Many of the monochrome monitors from the turbo XT era were dual frequency, and are able to sync to a 15.7khz CGA video signal. (And thanks to the awful CGA palette, a lot of games actually look better in 4 shades of amber/green than they do on an RGBI colour display!)

I don't see any executable code in the ROM dump so it isn't an EGA card.

There might be some driver utilities installed on the machine's fixed disk. I think these dual mono/CGA cards could usually switch modes via software, and the DIP switches just set the default mode to use during boot.

I would also suggest trying to source a 9-pin monochrome CRT. In my region they still show up from time to time and are practically free, unlike colour displays which are starting to become unobtanium.

What is the frequency of the X1 at the bottom left? Usualy there is
MDA 16.257 MHz
Hercules 16.000 Mhz

But indeed there is too much RAM for one of these cards.

You could try this to test the card 😉
6€ MCE2VGA replacement - CGA/EGA/HGC capture with logic analyzer

kdr wrote on 2021-07-25, 21:04:

I wouldn't be surprised if it is a combo MDA/Hercules/CGA card. Many of the monochrome monitors from the turbo XT era were dual frequency, and are able to sync to a 15.7khz CGA video signal. (And thanks to the awful CGA palette, a lot of games actually look better in 4 shades of amber/green than they do on an RGBI colour display!)

Yeah, that's probably the case. I just noticed the DIP switches on the motherboard are set to the "CGA" position, and going by the speaker beeps it seems to POST correctly under that configuration. Still, I won't be able to confirm until I get a display.

kdr wrote on 2021-07-25, 21:04:

There might be some driver utilities installed on the machine's fixed disk. I think these dual mono/CGA cards could usually switch modes via software, and the DIP switches just set the default mode to use during boot.

Unfortunately the machine came only with this card, and a Multi IO card with serial, parallel, clock/battery and floppy controller. It seems to be quite a bare bones machine for 1990-1991, with a single 360K 5.25'' floppy drive.

kdr wrote on 2021-07-25, 21:04:

I would also suggest trying to source a 9-pin monochrome CRT. In my region they still show up from time to time and are practically free, unlike colour displays which are starting to become unobtanium.

I'll be on the lookout for old 9-pin monitors, in any case the RGBtoHDMI is cheap enough and supports MDA/CGA so hopefully it will work with this card.

Predator99 wrote on 2021-07-25, 21:30:

What is the frequency of the X1 at the bottom left? Usualy there is
MDA 16.257 MHz
Hercules 16.000 Mhz

The oscillator is 16.000MHz, so I guess that would mean Hercules? What is the setting normally used in the DIP switch of the motherboards for Hercules cards? My motherboard only has MDA/CGA/EGA options, it was set to CGA when I got it.

Predator99 wrote on 2021-07-25, 21:30:

You could try this to test the card 😉
6€ MCE2VGA replacement - CGA/EGA/HGC capture with logic analyzer

Very interesting, didn't know about that! Also, I'm going to dump the motherboard BIOS and add an entry to your XT BIOS Collection thread 😉

TheMobRules wrote on 2021-07-25, 21:47:

Predator99 wrote on 2021-07-25, 21:30:

What is the frequency of the X1 at the bottom left? Usualy there is
MDA 16.257 MHz
Hercules 16.000 Mhz

The oscillator is 16.000MHz, so I guess that would mean Hercules? What is the setting normally used in the DIP switch of the motherboards for Hercules cards? My motherboard only has MDA/CGA/EGA options, it was set to CGA when I got it.

The 16.257MHz (original IBM MDA and EGA clock) and 16.000MHz (usual clone clock) are considered equivalent for video timings. The difference of around 1.6% doesn't matter for monitors being able to sync to it. As your card has 128K of RAM, it has enough RAM to support Hercules (you need 64K), CGA (you need 16K) and even some extended modes. So I guess given suitable DIP switch settings, the card might be Hercules compatible, but it still can be CGA compatible with other DIP switches. For CGA video, you need 14.31818MHz. You do not find an oscillator with that frequency on your card, but that doesn't tell you anything. This clock frequency is available on the ISA bus at the pin called "OSC", and the orgininal CGA card, and most CGA/Hercules combo clone cards, and even the original IBM EGA card (in CGA-compatible modes) take the 14.31818MHz clock from the ISA bus connector, so they don't have any oscillator for that frequency on the card.

TL;DR: Just because there is a Hercules compatible crystal oscillator on your card, that doesn't mean the card can't run in a CGA compatible mode producing CGA video timings.

TheMobRules wrote on 2021-07-25, 21:47:

What is the setting normally used in the DIP switch of the motherboards for Hercules cards? My motherboard only has MDA/CGA/EGA options, it was set to CGA when I got it.

There isn't a Hercules setting. But a Hercules (or compatible) card also acts as an MDA for text mode.

The BIOS only has direct support for MDA and CGA cards (which is why these don't have their own video BIOS). The switches on an XT motherboard inform the BIOS where you want the default video output to go. The "EGA" option is actually the same as "no video card installed", which means that the system BIOS won't try to initialize any cards. That's because the EGA has its own video BIOS onboard.

I'm not thrilled about resurrecting my own thread, but with the help of an RGBtoHDMI I was able to test this card, and wanted to share my findings in order to give this some closure and to keep it for reference in case anyone else happens to find one of these cards.

As expected, this card is both monochrome/CGA compatible. The default settings seem to work fine for Hercules/MDA:

• JP2 & JP3 set to 1-2
• All DIP switches set to ON except for #8

In order to enable CGA mode, the following settings worked for me:

• JP2 & JP3 set to 2-3 (this grounds pin 7 -mono video- and connects pin 3 -red-)
• Set switch #1 to OFF

With the above settings, it displayed all CGA modes in CheckIt tests correctly. Not entirely sure what the other switches do (some seem to enable and control the parallel port I/O address which isn't even populated, so it's useless, and switch #4 needs to be ON or I'll get missing video card beep code).

TheMobRules wrote on 2022-05-18, 18:01:

Not entirely sure what the other switches do (some seem to enable and control the parallel port I/O address which isn't even populated, so it's useless, and switch #4 needs to be ON or I'll get missing video card beep code).

Perhaps there might be a switch that toggles between the normal (2-dot) and 'thin' (1-dot) fonts?
From your dump of the character ROM it appears to have both versions for CGA (8x8) as well as monochrome (9x14):

Totally boring factoid: the "thin" 8x8 font (second from left) is identical to the Sperry PC's on-board video charset. Which makes sense, since the Sperry PC was also manufactured by Mitsubishi.