I think you have something of a double problem, newer cards not liking monitors that don't either had DDC or are able to detect with old school presence detect coding, or don't have 75ohm loads detected on R G and B, with only G in this case presenting a load...

AND...

Not doing the old standard mono mode of synch on green.

Possibly adding resistors to load R and B outputs (68 ohm to ground, nearest value to 75) will get some functionality, where the VGA isn't aware it's supplying mono so R and B channels completely absent instead of represented in luminance on green, so some things invisible... and also that doesn't fix the synch.

So.. full solution might be an adapter board that correctly mixes luminance to single output, green, and also combines synch signals, while giving the card side what it needs to "see" i.e. ~75Ohm load on all channels and older presence detect convention.

The "RCA converter" in your photo is also a scaler, it only outputs 15 kHz (standard TV compatible) which won't work on this 31 kHz only monitor even if you added a sync separator...

The VGA converter indeed doesn't like your monitor, you might try buying a VGA EDID emulator dongle (or building your own for the next reason I'm about to mention), but as you can see here some don't care and work just fine: https://i.redd.it/mo8938pyrrj71.jpg

Then you will probably find out most GPUs, and probably all of those converters, don't implement B&W mode (only the Intel i815, of those I have, does) so you'll get the pictures in the left column of that photo, you need to add a mixer like the top part of https://i.stack.imgur.com/VkJij.gif to get what you see on the rightmost examples!

(connect the syncs straight through, same for the grounds and also all together, "video" to pin 2)

I actually made an EDID for the 8503 but never got to try it, sold it before I could bother to add that building block to my mixer (totally independent, just program a 24C02 I2C EEPROM appropriately and connect literally half of it to power/ground/clock/data)

I see, I've come to the right place. Thanks so much for your answers.

I'm out of my depth a little bit.
So @Ryccardo you mean that if i build that small circuit myself, and work with a direct HDMI-VGA adapter, this could potentially work? Or is the EDID still needed?
I'm building an enclosure as well so some soldering would be easier than having 4 adapters in a row.

I have found this product:
Delock edid emulator vga - vga
https://www.delock.de/produkt/63326/technisch … ?setLanguage=en

So with a default HDMI/VGA converter and this emulator I would circumvent the 15kHz/31kHz problem with my RCA scaler, or am I missing something?
Problem with the B&W mode, I guess i can live with just making the source completely green (its just a video, so just tint it black+green). Not elegant, but for a one-off installation..

The monitors take 31khz VGA 640x480 so what are you trying to achieve with the RCA scaler?

falue wrote on 2023-03-15, 16:54:

So @Ryccardo you mean that if i build that small circuit myself, and work with a direct HDMI-VGA adapter, this could potentially work? Or is the EDID still needed?

A different DAC should work (mine is whatever NuovaVideoSuono was rebranding at some very unknown time in the 2010s) but indeed that means trial and error...

falue wrote on 2023-03-16, 10:50:

I have found this product:
https://www.delock.de/produkt/63326/technisch … ?setLanguage=en

I would pass and look for something else - or just make it: apart from generally being an expensive brand (though a quality one!) something that declares ridiculously high timings (or allegedly copies the monitor without making it clear how to operate that feature) isn't much better than nothing for a 31 kHz only monitor, even though it might do if you're going to remote into the computer to manually set the video mode (something I never really tried but wouldn't be surprised if it's hard, given my experience at failing to use xrandr from a non-X console...)

falue wrote on 2023-03-16, 10:50:

I have found this product:
So with a default HDMI/VGA converter and this emulator I would circumvent the 15kHz/31kHz problem with my RCA scaler, or am I missing something?

Well, yes, by not using the RCA one which is useless for the job 😀
You only need that (and even then it's the lowest common denominator) for a TV-compatible monitor or video recorder (=15 kHz), like a Commodore 1084S or, well, the composite input on any ordinary TV!

falue wrote on 2023-03-16, 10:50:

I have found this product:
Problem with the B&W mode, I guess i can live with just making the source completely green (its just a video, so just tint it black+green). Not elegant, but for a one-off installation..

Well, in this case, nice workaround (you could equally use a greyscale filter which is probably more common, possibly even in your video player) 😀

All right, sorry for my slow answers.
So the RCA scaler is out, got it.

So for clarification, it's a mess in my head. The terminology is hard here.

I would pass and look for something else - or just make it

So by "it" you mean build a custom VGA EDID emulator dongle like that https://i.stack.imgur.com/VkJij.gif combined with a "24C02 I2C EEPROM" EDID, but i would find a HDMI/VGA adapter with the correct DAC which i find at random?

Or is it just any HDMI/VGA adapter and that little circuit:
https://i.stack.imgur.com/VkJij.gif

Just try the simple circuit first, it may be enough to activate the output with analog detection, and force res in the OS, but the EDID thing is to make it work for everything everywhere plug and play, which you may not need.

So I've tested this circuit with some success, but had troubles wiring the outgoing d-sub connector.
First of all, my windows machine now detects the adapter as a VGA monitor and i can adjust the resolution, which made me happy.
My MAC can't handle the adaptor thought (endless screen blanking), and i cant test it right now on my raspberry pi but i assume if it works on windows, it will work on the raspi. I will be able to test this if i actually get a picture.

The image on the screen is scrambled:

I can't find a pinout for 7-pin d-sub monochrome VGA connectors.
So i figured, as the VGA plug of the monitor has only 7 pins (2,5,7,10,11,12 and 13) i would wire them just trough as good as i can.

Pin 1,2 and 3 wired to pin 2/green
pin 13/h-sync directly to pin 13/h-sync, does seem to make little sense.
What does pin 15 do? On newer VGA it seems to be N/C.

I guess i have to still change the v-sync/h-sync signals somehow.
Any ideas on how to wire this?

Ah, remove the 3 components on the bottom of the drawing and just connect 14 to 14 and 13 to 13, leave them both completely disconnected from 2 (your monitor is not sync on green, and even then it would only work with negative sync) and it should work 😀

15 and 12 are I2C (don't remember which one is clock and which data), where you could connect an EEPROM, no need to connect them to the monitor in this case!

Don't do this. I had a IBM 9" mono with VGA plug like this and does work with regular VGA card without setting any dip switch on a 386DX 25 back in the day. The VGA converter you are using is for DCC on two different pins and does not support this.

The 8503 support different modes up to 640 x 480 only.

The video input for monitor is on green signal pin with green ground pin and VGA plug does have detection pins to ground or left floating, so monitor tells video card it is mono or color and resolution.

Details.
http://oldcomputer.info/hacks/vgatool/index.htm

Besides, do this with ISA VGA card or PCI card on a Pentium, or even PIII.

Cheers,

@ryccardo thanks, i will try this.

pentiumspeed wrote on 2023-03-26, 20:36:

The VGA converter you are using is for DCC on two different pins and does not support this.

So the question is: Is there a VGA converter that does support this? how can i find products that do? Most websites do not specify anything in detail on those converters.

pentiumspeed wrote on 2023-03-26, 20:36:

Besides, do this with ISA VGA card or PCI card on a Pentium, or even PIII.

Problem is, i have to use a raspberry pi due to project specifications.

Most if not all these converters are too new to care for the pre-EDID system (the one with ID 0/1/2/3 pins open or grounded) but conveniently the Pi should make this easy:

hdmi_drive=1
hdmi_group=2
hdmi_mode=4
and turn off the new KMS video driver or it'll override these as it loads (or figure out the kernel command line equivalents for these options)

These were enough to get a stable VGA picture (apart from the lack of proper black and white support) on my setup 😀

Thank you ryccardo. Sorry for slow answering, but I try to solve a lot of problems at the same time on this massive project with lots of moving parts, one of which is this beautiful display problem.

I made some progress:

this is, in fact, the desktop image. The v-sync seems accurate (matches the height of my desktop image), but h-sync is off. maybe this is because the screens do have a max resolution of 640 x 480 and the adapter i'm using does output something different?

i soldered it like this:

and set

Ryccardo wrote on 2023-03-27, 20:29:

hdmi_drive=1
hdmi_group=2
hdmi_mode=4

but i could not figure out how to disable the "KMS video driver". Besides, i need to use hdmi out because I have a video wall splitter, so i'm not sure why I should disable hdmi at all:

@pentiumspeed

pentiumspeed wrote on 2023-03-26, 20:36:

Don't do this.

I'm still trying to figure out why you discourage ryccardos solution because i do not understand how this is relevant to my raspberry pi setup or the problems at hand. Also, or most importantly, I try really hard to understand what you're saying at all. Its a bit over my head.
Which dip switches? Why 386DX 25? Why recommend ISA VGA cards apart from me using a raspberry pi? Why different approach for the detection pins even though it seems to be working somewhat now?

Why is it so important to use an HDMI-VGA converter? 🤷‍♂️
- I mean, I'm using one for my TFT monitor, as well. But that's an ordinary VGA panel.

For controlling such ancient monochrome monitors, wouldn't it be better to use the GPIO pins directly? A more analogue approach, so to say.

https://www.kickstarter.com/projects/pisupply … or-raspberry-pi

Or, how about using the Composite output? If it's software programmable, VGA timings might be possible.
An optional sync stripper/decoder might then be needed additionally, sure.
Something that filters h/v sync from CVBS/VBS signal and makes it available independently.

Edit: And why mixing RGB pins? Wouldn't green be good enough? AFAIK, even if it's not converted to grayscale,
the green component of an RGB picture is close enough to a real monochrome picture.

Jo22 wrote on 2023-04-15, 15:59:

Why is it so important to use an HDMI-VGA converter? 🤷‍♂️
(...)
wouldn't it be better to use the GPIO pins directly?

good questions! few reasons:
1. didn't think that thats possible with GPIO pins so thats why i didn't check
2. if there's a simple adapter i could buy or fabricate with a few resistors, that would be easier
3. I need 1 desktop split (not duplicated!) among 4 screens, so 4 different images on each, hence the video wall controller. And cheap & available ones in my country only come in HDMI flavour.
4. almost all my GPIO pins are occupied with buttons, LEDs and dials.

The "Gert VGA 666" you posted uses "all but 6 GPIO pins" for one monitor, so i think this is not my solution.
If you still think GPIO would be beneficial, I'm all ears!
The amount of screens could be dropped to only 2 if that would help, but 4 was the goal.

Jo22 wrote on 2023-04-15, 15:59:

Or, how about using the Composite output?

Because of the video wall controller. If there's one thats working with VGA or composite, that might be an improvement, but currently there's only the HDMI one available to me.

Jo22 wrote on 2023-04-15, 15:59:

Edit: And why mixing RGB pins? Wouldn't green be good enough?

Yes green would be enough but that was fun and fast and does not complicate things? Or does it?

falue wrote on 2023-04-15, 13:58:

this is, in fact, the desktop image. The v-sync seems accurate (matches the height of my desktop image), but h-sync is off. maybe this is because the screens do have a max resolution of 640 x 480 and the adapter i'm using does output something different?

Anyone an idea how to solve this? I'm stuck here.