I'll risk a guess here and assume that chatgpt is hallucinating as usual referring to the MS Basic compilers NOCGA.OBJ file. If you weren't targeting CGA systems you'd link this file to exclude things you didn't need, thus reducing size.

Also please don't butcher it to remove the chip!

Hi there. This seems to be the computer, I guess?
https://www.valoroso.it/frael-king/

There are screenshots of the motherboard..
I spot a jumper to select between PAL TV and TTL Monitor? Maybe that's CGA/MDA or CGA/Hercules switch?

If so, the latter setting might be more compatible with co-existing with VGA..
Because, a Hercules/MDA card in plain text-mode merely use 4 KB of RAM and doesn't collide with A-segment used by EGA/VGA.

Does your pc see the VGA Bios? Type
debug
d C000:0
And show us the output.

Hi there. This seems to be the computer, I guess?
https://www.valoroso.it/frael-king/

Yes, the link is right.

Predator99 wrote on 2025-09-27, 09:53:

Does your pc see the VGA Bios? Type debug d C000:0 And show us the output. […]
Show full quote

Does your pc see the VGA Bios? Type
debug
d C000:0
And show us the output.

Yes: I can see the VGA bios at boot, and:

"reserved for IBM compatibility.....10/18/93........D4.01E..........Copyright 1988-1991 TRIDENT MICROSYSTEMS INC."
It's a Trident TVGA9000i-1, 8 bit ISA; It outputs in black and white, no graphics mode, only text: the games doesn't start.
In some sporadics moments It shows the VGA BIOS writings at boot in colours, but I don't remember if It continues to boot, and if It does It in colour mode.

Then I agree with Jo22 there might be a resource conflict. Is there a BIOS Setup where you can disable CGA? Can you provide a dump of the ROM?
Your Idea to remove CGA ram is also an option. Its on a socket? If yes there is no risk to try without.

Randomly starting with color or monochrome reminds me of a known Trident issue that happens when connecting it to monitors newer than its time. IIRC it was trying to determine the monitor's type (color vs mono) via a data pin that got repurposed on newer monitors, so it seems it gets fed "random data" at boot, hence the random choice of color or mono.

I suggest trying a different VGA card. The fact that the VGA card POSTs means the integrated CGA is cooperating properly.. so I think you don't need to tinker with jumpers even.. just the mono/color switch on the back of the mobo.

Well known problem with TVGA cards misinterpreting a DDC signal as random high/low/color/monochrome, trident's smonitor.exe utility will force the card into color mode. Nothing to do with the onboard CGA.

jmarsh wrote on 2025-09-28, 09:57:

Well known problem with TVGA cards misinterpreting a DDC signal as random high/low/color/monochrome, trident's smonitor.exe utility will force the card into color mode. Nothing to do with the onboard CGA.

Well, there may be two issues here. One issue is that TVGA cards use the classic IBM monitor ID pins to detect whether a grayscale VGA monitor or a color VGA monitor is attached. This is the "well known issue" already referred to in this thread. If you have a DDC capable monitors, the TVGA BIOS indeed randomly detects the monitor as monochrome or color monitor. If a monochrome monitor is detected, the VGA BIOS outputs grayscale video only.

Another issue is that the VGA BIOS auto-probes for CGA and MDA cards being installed in the system. If there is none (the typical case), the VGA BIOS runs in "catch-all" mode, and handles both the MDA/EGAmono-type modes 07/0Fh (switching the VGA card to use ports 3Bx for the CGA/MDA-inspired CRTC, just as the MDA did), and CGA/EGAcolor/VGA modes 0-6, 0D.h.13h (switching the VGA card to use ports 3Dx for the CGA/MDA inspired CRTC, just as the CGA did). On the other hand, if the onboard CGA is detected by the VGA BIOS at POST time, the VGA card locks into "MDA replacement" mode, and passes all modes to the CGA card except modes 7 and 0Fh (the EGA mono graphics mode nearly no one uses).

It is important to understand that these two issues are unrelated. Even if the TVGA BIOS misindentified a DDC-capable monitor as monochrome monitor, and it outputs grayscale, the card will still run in "catch-all" mode and allow all CGA, MDA, EGA and VGA text and graphics modes. On the other hand, the lock-in to "MDA replacement" mode happens only due to a CGA being present and not due to the monitor type.

montezuma iii wrote on 2025-09-27, 21:40:

It's a Trident TVGA9000i-1, 8 bit ISA; It outputs in black and white, no graphics mode, only text: the games doesn't start.
In some sporadics moments It shows the VGA BIOS writings at boot in colours, but I don't remember if It continues to boot, and if It does It in colour mode.

The point about "no graphics mode" make me think the detection of the onboard CGA is important in this case, setting the VGA card into MDA replacement mode, although the second part of this quote about some sporadic moments very much sounds like the DDC problem.

As a final note: The "catch all" mode is new with the VGA card. The EGA card always either operated in "MDA replacement" mode, outputting video at the scan frequency of the MDA card, only supporting modes 7 and 0Fh, or in "CGA replacement" mode, outputting video at the 200-line CGA scan frequency or the 350-line EGA scan frequency. The EGA BIOS also did not auto-detect other cards, but it required the DIP switches to select "CGA replacement" or "MDA replacement" mode. This was actually a good thing, because of the different scan rates in the different modes. OTOH, VGA always scans at 31.5kHz, no matter whether it displays a CGA-type or an MDA-type mode, and no matter whether a grayscale VGA monitor or a color VGA monitor is connected. MDA, CGA and EGA monitors are not supported (there are clones that do, but I consider them out-of-scope when describing the features common to all VGA compatible video cards).

Predator99 wrote on 2025-09-28, 06:20:

Then I agree with Jo22 there might be a resource conflict. Is there a BIOS Setup where you can disable CGA? Can you provide a dump of the ROM?
Your Idea to remove CGA ram is also an option. Its on a socket? If yes there is no risk to try without.

The BIOS in the pc hasn't a setup, I tried stock BIOS and GLABIOS: no setup; no jumpers and dip-switches to disable CGA.
The CGA RAM is socketed and I've tried to removing It without obtaining results, the GPU is a soldered SMD: what does could happens by removing It: damages?

just the mono/color switch on the back of the mobo.

The switch isn't for selecting mono/color: It is for selecting something like CGA or RF modulator video.

jmarsh wrote on 2025-09-28, 09:57:

Well known problem with TVGA cards misinterpreting a DDC signal as random high/low/color/monochrome, trident's smonitor.exe utility will force the card into color mode. Nothing to do with the onboard CGA.

I've tried yet the smonitor utility: It writes "color", but I can see only black/white text.

Which could It be an alternative compatible/good VGA card? The PC has a NEC V20 cpu and 768k of RAM

So with the 2 CGA RAM-ICs removed it still starts with CGA..? Or didnt you manage to remove them? Its not difficult, you need a small screwdriver.

When you insert the VGA: Do you see the all the BIOS/DOS Messages on your VGA or is it still on the CGA?

Do not remove the SMD-IC...

Maybe there is a small chance that VGA takes over control if you initialize it again, type:

debug
a
call far c000:3
int 20
(enter)
g
q

Predator99: this trick doesn't work: still b/w.
I seem to remember when I tried to remove the video-ram chips that the pc produced garbage/colors in the CGA out and still B/W in the VGA out.

Hi, may I ask if there's a specific reason for VGA?
I don’t mean to judge, I have two XTs (CGA+HGC, VGA) myself, but I'm curious..

Because if it's about colour graphics in older games, then an Hercules InColor card could work in principle.
Users of PC1512 could install that card, too.
A list of games can be found here: https://www.mobygames.com/attributes/attribute/579/

Also, if the CGA chip (Winbond SMD?) is enhanced it may support Plantronics mode.
Which some Sierra games now have a driver for (also, there's Planet X3 and Petscii Robots).
GEM and some paint programs also supported Plantronics.

Forget the b/w issue.
As explained, this is not related to the CGA/VGA conflict and can easily be resolved with another card. Take a closer look if VGA works (in b/w) with the RAM removed.

With the video-ram removed, I can confirm: garbage colors in the cga output (but I think It's normal) and black/white text in the vga output

...And I can see the bios/post of the vga card

I am currently facing the same issue with a damaged Schneider EURO PC. It has onboard CGA and the external VGA only works the same way as you describe. The BIOS can switch the CGA to Hercules or disable it. But as the RTC on my board is damaged this does not work. CGA enabled seems to be the default setting. I currently try to find a way to switch manually.

Maybe its possible for your integrated CGA, too.

I am quite sure there is no generic "NOCGA"-util.

Couldn't be the gpu on my board is defective? There are no jumpers on the mobo

montezuma iii wrote on 2025-10-03, 20:08:

Couldn't be the gpu on my board is defective? There are no jumpers on the mobo

(P.S.: I mean the gpu on the vga, not the cga on the mobo)