https://choiceprinters.com/video/TTL/TVM_MD3N.html

RGB Monitor sounds like CGA only unless it also does “Analog” which can run with Amiga

That's definitely not an EGA card: it only has two two 64Kx4 DRAM chips = 64KB with an 8-bit wide graphics bus. EGA cards use a 32-bit wide graphics bus with (usually) eight 64Kx4 DRAM chips = 256KB.

Most likely you have a MDA/Hercules/CGA combo card, and there's a good chance that the TVM monitor can sync to both 15.7khz (CGA colour) and 18.4khz (MDA/Hercules mono). The selector switch on the front panel probably chooses how to interpret the video data (RGBI colour, green monochrome, or amber monochrome).

kdr wrote on 2021-06-22, 00:01:

Most likely you have a MDA/Hercules/CGA combo card, and there's a good chance that the TVM monitor can sync to both 15.7khz (CGA colour) and 18.4khz (MDA/Hercules mono). The selector switch on the front panel probably chooses how to interpret the video data (RGBI colour, green monochrome, or amber monochrome).

I don't think we have strong support for the assumption that the monitor supports 18.4kHz. We have clear evidence that the monitor does not support MDA/Hercules mono cards, though: The OP mentions that pin 7 (secondare blue on EGA) is missing in the connector. That's the main video signal on MDA/Hercules. On the other hand, there were dual-scan monitors that could sync to MDA text mode frequencies as well as CGA graphics mode to combine the good MDA text quality with the CGA graphics capabilities. I have no kind of proof this monitor is not dual-scan, so it might work with special graphics cards that can output RGBI text with MDA timings.

https://www.phantom.sannata.org/viewtopic.php?t=26278
https://books.google.hu/books?id=mi8EAAAAMBAJ … %20md-3&f=false

mkarcher wrote on 2021-06-22, 17:45:

I don't think we have strong support for the assumption that the monitor supports 18.4kHz. We have clear evidence that the monitor does not support MDA/Hercules mono cards, though: The OP mentions that pin 7 (secondare blue on EGA) is missing in the connector. That's the main video signal on MDA/Hercules.

Ah yeah, missed that part. I suppose that means the monitor just supports standard CGA with a 'fake monochrome' 15.7khz mode. (I have a Philips CM8833-II that features a "Green" switch on the front panel, which simply disables the red and blue video signals when activated, so it's not unheard of.)

Apologies for only replying now - been a bit of a crazy week.
I think it's clear, based on the physical connector and links to some material provided, that this is definitely a CGA colour monitor with the option to switch (on the front) between an amber or green monochrome mode.
What initially threw me off was the fact that, on the Wikipedia page, the TVM monitor was being presented as an "EGA" monitor. Unfortunately, I didn't pay close attention to the connector (which has a missing pin 7). I do believe that TVM made a similar looking monitor that was EGA compatible, but I haven't yet been able to determine those model numbers.
After gathering my thoughts, my takeaway as follows:

1. In order for a monitor to be truly EGA compatible, all of the 9 pins must be there. If your connector has a missing pin 7, then it cannot be an "enhanced EGA" monitor (more on this below) capable of supporting the 350-line mode.
2. However, that doesn't mean that should the monitor have all the pins (including pin 7), that it is an "enhanced" EGA monitor. The best way to confirm is to check for continuity between pins 1 & 2 (i.e., if both pins are connected to ground). If there is continuity, then (as mentioned previously), it's most likely a dual sync monitor capable of supporting MDA & CGA (but not "enhanced" EGA).
3. What is interesting is that this monitor also has an amber monochrome mode. I can understand that it's fairly easy to simulate green monochrome mode (by simply disabling the red & blue signals), but amber is a bit more tricky.
4. The EGA standard was backwards compatible with CGA, which means it had a 200-line mode and an "enhanced" 350-line mode that supported higher resolutions, but still capable of displaying up to 16 colours (provided you had enough memory on the graphics card).
5. Many early EGA cards were actually 8-bit cards and only came with 64KB of onboard RAM (some of them were upgradeable to support more RAM).
6. You can use an EGA card to drive a CGA monitor, but you will be limited to 200-line mode. Most EGA cards from that era did have jumpers or switches on the card to disable the 350-line mode to ensure compatibility with older CGA monitors and also to avoid damage to the card itself.
7. Most EGA games only supported 320x200 16 colour mode which means you can play all your favourite EGA games with an EGA card driving a CGA monitor (just be sure to jumper the EGA card to 200-line mode).

jesolo wrote on 2021-06-26, 14:16:

However, that doesn't mean that should the monitor have all the pins (including pin 7), that it is an "enhanced" EGA monitor. The best way to confirm is to check for continuity between pins 1 & 2 (i.e., if both pins are connected to ground). If there is continuity, then (as mentioned previously), it's most likely a dual sync monitor capable of supporting MDA & CGA (but not "enhanced" EGA).

If all 9 pins are in the connector, the monitor can still be a CGA-only or MDA-only monitor. I'm sure some vendors used generic 9-pin plugs on their monitor even of not all of the pins are connected. Before concluding that a 9-pin monitor with 1&2 short is likely a dual-sync monitor, I would check that pin 7 is actually connected to something, by using a meter in diode check mode with the red wire connected to ground and the black wire connected to pin 7. I expect a non-infinity reading through (parasitic / protection) diodes on that check if pin 7 is connected.

mkarcher wrote on 2021-06-26, 14:24:

jesolo wrote on 2021-06-26, 14:16:

However, that doesn't mean that should the monitor have all the pins (including pin 7), that it is an "enhanced" EGA monitor. The best way to confirm is to check for continuity between pins 1 & 2 (i.e., if both pins are connected to ground). If there is continuity, then (as mentioned previously), it's most likely a dual sync monitor capable of supporting MDA & CGA (but not "enhanced" EGA).

If all 9 pins are in the connector, the monitor can still be a CGA-only or MDA-only monitor. I'm sure some vendors used generic 9-pin plugs on their monitor even of not all of the pins are connected. Before concluding that a 9-pin monitor with 1&2 short is likely a dual-sync monitor, I would check that pin 7 is actually connected to something, by using a meter in diode check mode with the red wire connected to ground and the black wire connected to pin 7. I expect a non-infinity reading through (parasitic / protection) diodes on that check if pin 7 is connected.

Good advice - rather be safe than sorry.

jesolo wrote on 2021-06-26, 14:16:

[*]You can use an EGA card to drive a CGA monitor, but you will be limited to 200-line mode. Most EGA cards from that era did have jumpers or switches on the card to disable the 350-line mode to ensure compatibility with older CGA monitors and also to avoid damage to the card itself.
[*]Most EGA games only supported 320x200 16 colour mode which means you can play all your favourite EGA games with an EGA card driving a CGA monitor (just be sure to jumper the EGA card to 200-line mode).[/list]

Yep, adding an EGA clone card must have been a cheap way to upgrade an old PC / XT class machine because it could work with the existing CGA or MDA display. Going to VGA meant buying a new display.

jesolo wrote on 2021-06-26, 14:16:

[*]Many early EGA cards were actually 8-bit cards and only came with 64KB of onboard RAM (some of them were upgradeable to support more RAM).

I'm not so sure about this. PC Magazine's August 1986 issue had a big review of the then-brand-new EGA clones, and (aside from the original IBM card) only 2 of the 11 clones even offered a 64KB version; the remainder were only available fully loaded with 256KB. Perhaps more 'budget' 64KB cards were introduced once the EGA clone market really took off?

kdr wrote on 2021-06-27, 00:19:

it could work with the existing CGA or MDA display.
Going to VGA meant buying a new display.

Not always,
I have had many early VGA cards that had a 9 pin and could run a CGA monitor with various results and compatibility issues.

Also I did own a clearly labeled VGA hybrid card with l128k upgradable to 256k

Here's pics of my TVM EGA MD-7E monitor:

Caluser2000 wrote on 2021-06-27, 05:59:

Here's pics of my TVM EGA MD-7E monitor:

Thank you for the pictures.
Your monitor is quite similar to the one in the YouTube video I linked to in my first post.
Some interesting observations:

1. The monitor does look very much identical to the CGA variant (at least from the front)
2. on the back I noticed two differences, namely the fan and the extra two knobs to the right hand side

Just out of curiosity - what are the functions of those two additional knobs on the right hand side at the back? I presume the other two (closer to the power connector) are also Vhold & Vsize?