Or the Video-RAM on the VGA board?

Personally, judging by the results, I think what mkarcher wrote makes most sense here.
The VGA BIOS likely detects presence of an existing CGA card (MC6845) and switches the VGA chip into MDA mode (in simple words).
By running MSD or CheckIt, it's maybe possible to check of what type primary/secondary video is.

Yes I agree. The information provided by mkarcher regarding the CGA detection by a VGA (but not by EGA) is new to me and very important for my current project 😀

My EURO-PC works with a EGA card but not with a VGA.

Maybe you can also try an EGA card?

If yes, a solution would be to delete the CGA detection from the VGA-BIOS?

Both GlaBios and Checkit write: Video adapter: VGA, MSD is more precise and writes: Video Adapter Type: VGA. Display Type: VGA Monochrome, Video Mode: 7, Secondary Adapter: CGA, Manufacturer: Quadtel (maybe the firm who assembled the open source board?), Vesa OEM Name: Trident Microsys...

Try running the attached color.com before anything else and tell us if anything changed:
(the file's origin is this thread on vcfed)

1) Color.com crashes, but I removed the video CGA ram on the mobo, (to test the vga without them): should I have to re mount them?
2) I've got an eprom/eeprom programmer, and I'd like to do a further step:

Predator99 wrote on 2025-10-04, 09:54:

If yes, a solution would be to delete the CGA detection from the VGA-BIOS?

How can I do this?

montezuma iii wrote on 2025-10-06, 20:15:

Predator99 wrote on 2025-10-04, 09:54:

If yes, a solution would be to delete the CGA detection from the VGA-BIOS?

How can I do this?

I don't think deleting the CGA detection from the VGA BIOS is a good idea. While this will allow the VGA card to be set to color modes, it will not turn off the on-board CGA chip, which will still respond to reads to I/O port 3D8, and memory reads in the B800..BBFF (likely BFFF) range. This will yield bus conflicts if there is a buffer chip between the (removed) CGA memory and the ISA bus, which is quite likely to be the case. While you might get away with the CGA memory installed, because the VGA and the CGA card will always read the same value, this will only work for the 16K of memory a CGA card has, not for the full 32K of CGA memory. I'd guess reading the HSYNC/VSYNC status from 3D8 will be the main issue if both the onboard CGA solution and the VGA card in color mode are active at the same time.

I think the video CGA ram is 16k only in total

montezuma iii wrote on 2025-10-06, 21:27:

I think the video CGA ram is 16k only in total

But it's being duplicated in the address space, maybe.
A real IBM CGA card has 16KB, as well, but the frame buffer area is 32KB long.

So: could others VGA cards work? I've got a TVGA8900D-R (chip), model T8900D-i1, K928: It has a 16 bit ISA connector, but there are three jumpers marked as jp6 and one single jp7: now It does black screen; I can hear the GlaBios beep (PC bios) and It has no bios rom (VGA bios).
Or could It be an hardware problem (defective GPU, video ram...) of my TVGA9000i?
Otherwise could you suggest some good VGAs, 8 bit ISA, or 16 bit ISA/8 bit compatibles? I'd like a card who does all the video standard (MDA, CGA, EGA and VGA), I could renounce to the MDA, but I'd like that all the games runs (CPU and ram allowing), with colors.

montezuma iii wrote on 2025-10-07, 22:24:

So: could others VGA cards work? I've got a TVGA8900D-R (chip), model T8900D-i1, K928: It has a 16 bit ISA connector, but there are three jumpers marked as jp6 and one single jp7: now It does black screen; I can hear the GlaBios beep (PC bios) and It has no bios rom (VGA bios).

It does have a VGA BIOS, but it is integrated in the TVGA8900D-R chip (the "R" is for the integrated ROM). So for all practical purposes, the cards behaves as if it has a dedicated ROM chip.

The reason you get issues with many fast 16-bit cards in 8-bit slots is that the address signals A17-A19 are twice on the ISA bus: Once in a variant that appears later and stays valid for the whole cycle (SA17..SA19), and another edition that appears early, allowing the card and mainboard to "prepare" an address, but may not stay valid over the whole cycle (so the next cycle can be prepared while this cycle is still running). This second set of signals is called LA17..LA19, and is only present on 16-bit slots. Also, there is a 1MB address space memory read/write signal pair called /SMEMR and /SMEMW, and a second signal pair that is also active for memory cycles exceeding 1MB, called /MEMR and /MEMW. Again, this second pair is only on the 16-bit connector. Unless a 16-bit VGA card is able to fall back to using only the signals located on the 8-bit slot, the card will not work in that slot. I tested on my XT, and I found one of my ET4000 cards and my ISA mach32 card to work, but a lot of other 16-bit cards did not work.

Given the jumper numbers you quoted, I could not identify your card on https://theretroweb.com/expansioncards/?items … Ids%5B0%5D=7971 , so likely its not there. But note how a "block of 3 jumpers" is included in the silk screen of two of the cards located there with "all open for 16 bit bus" (and all closed for 8 bit bus). Maybe you can use jumpers to make the TVGA8900D-R 8-bit compatible.

The issue that the on-board CGA card uses resources that conflict with a VGA card in color mode can not be resolved cleanly by using any kind of other VGA card, though.

mkarcher wrote on 2025-10-08, 05:53:

The issue that the on-board CGA card uses resources that conflict with a VGA card in color mode can not be resolved cleanly by using any kind of other VGA card, though.

I think same. The most "elegant" solution would be to gently remove the CGA's SMD (?) chip with a heatgun, if it's not linked to other circuits somehow.
I assume it's an Winbond chip or something. The kind of chip found on later Hercules/CGA combo graphics cards.
But it's only an assumption, because there's no information on the web and the few pictures available are low-res. :(

The question is however, if that wouldn't possibly ruin a perfectly fine CGA computer here.
This is the first model I've seen that has such a tidy mainboard with an RF (!) modulator.
Gaming wise, it's excellent for experiencing DOS games from the mid-1980s or to run early 8086 Unix systems such as PC/IX
that require an hardware-compatible CGA or MDA board.

https://de.wikipedia.org/wiki/PC/IX#Funktionen

mkarcher wrote on 2025-10-08, 05:53:

: TVGA 8900D-R: It seems the built-in bios isn't working, but I can hear the glabios boot beep, the card has an empty "slot" (not socketed), maybe I can make solder an eeprom with the bios from someone: could It be this the issue because the card isn't working even in B/W mode?
Does the TVGA 8900D-R and the TVGA 9000i has CGA compatibility (especially for games) so that I'd have no second thoughts by removing the CGA chip? Could It be quality loss in CGA mode/emulation?

Jo22 wrote on 2025-10-08, 07:38:

: Who could be equipped to remove the SMD chip: maybe the cellular phones repairers?

P.S.: I've noted that the GPU on some 9000i are marked as "9000i-1" and others "9000i-3": maybe the 9000i-3 is more updated? Which are the advantages?

Thanx for helping me

To repeat again: Do _not_ remove that IC 😉

As far as I can see on the photo you have an onboard "VDL C4" (sometimes also called UDL) chip like on this card
https://www.vgamuseum.info/index.php/cpu/item … l-unknown-model
So its a nice chip supporting Plantronics, other people are seeking for cards supporting this.

I am not sure if it can be switched to Hercules to avoid a conflict with VGA. However, it looks very similar to the Paradise PVC4, maybe its a clone? For the PVC4, a switching utility for the ATI Graphics Solution is available here
ftp://ftp.mindcandydvd.com/pub/drivers/ATI/Gr … ics%20Solution/
See this thread
Paradise PVC4 CGA card : looking for video BIOS [ROM restored !]

I also downloaded the driver disk / manual and will test the MS.COM switching utility on my Euro PC. I think there is a chance it also runs on you PC.

Some information about Plantronics:
Re: 1984 IBM 5170 286 6HZ 65kb The beginning

Predator99 wrote on 2025-10-18, 16:21:

I am not sure if it can be switched to Hercules to avoid a conflict with VGA.

If it can be switched, you likely have to clear bit 1 (value 0x02) at 0x40:0x87 to tell the VGA card to be active for color modes and hand over monochrome modes to the on-board MDA/Hercules. This bit has been used since the original IBM EGA to select between "EGA does color stuff" and "EGA does mono stuff". The new catch-all mode on the VGA, in which the VGA card auto-switches between doing mono stuff and doing color stuff, has no fixed configuration bit in the BIOS data area, but it varies between BIOSes how that catch-all mode is represented. If a VGA card already is in "mono only" mode because the POST detected the on-board CGA, you don't have to worry about catch-all mode, because it is already disabled. In non-catch-all mode, all VGA BIOSes I know behave EGA compatible and respond to 0x40:0x87 bit 1.

Predator99 wrote on 2025-10-18, 16:21:

To repeat again: Do _not_ remove that IC 😉

Ok: I will not remove It, but I'd be curious to know what could happen to the pc: could the whole pc to stop working? Which features would I lose?

Tried MS.COM with the MG1 option ("to allow a second graphic card"), but It crashes

montezuma iii wrote on 2025-10-19, 21:11:

Predator99 wrote on 2025-10-18, 16:21:

To repeat again: Do _not_ remove that IC 😉

Ok: I will not remove It, but I'd be curious to know what could happen to the pc: could the whole pc to stop working? Which features would I lose?

Hi, not sure, it depends on the chip and the circuit on the motherboard.
In best case, the graphics system would be inactive as if a dedicated CGA/MDA was removed from ISA slot.

But maybe removal isn't necessary, even?
If it's an one-in-all solution with built-in address decoders etc, then maybe it's enough to gently lift a single power pin of the IC to disable it?
Since many ICs that age (mid-late 80s, like the NEC V30) support tri-state etc the IC might just be hanging passively on the bus without disturbing it too much.

Edit: Depending on the circuit on the motherboard, it might also be possible to leave that IC alone and disable one (or a few) of the external ICs.
Buffers, address decoder ICs etc. The stuff that connects the IC to the bus.
From point of view of the rest of the system the graphics system would be unavailable, simply.
If that's possible, the IC can be left alone (as is). The through-hole chips (74xxx) can be easily replaced/re-installed compared to the CGA chip.

But again, that's just a guess. I don’t know the specs of the IC and can't predict anything.
Removing the whole thing needs care and isn't a project for beginners.
It's too easy to ripp off some pins or make shorts etc (can be fixed, but still).
I myself wouldn't do that until I had gained some practical experience. 😅

And of I bring the PC to a cellular phones repairing center: aren't them equipped for removing SMDs?