an MDA monitor, and you want to supply it signal from a VGA/DVI or HDMI out... interesting.

Yes, it's silly, I know. But it will be fun, I promise 😀

The hard part will be sending the resolution it needs, you'll have to create a custom resolution for it with right timings since the monitor is fixed freq and will not display any of the commonly available options.

Yes, I'm not clever enough to make my own converter.
However, there are plenty of converters out there for all kinds of vintage systems.
Surely there must be something that could do it?

If you had a newer MDA screen (not ibm) with pot adjustments for v/h hold/sync you could potentially run a vga signal through a cheap scan converter with rgb + sync and wire only R B HV getting a 4 grayscale display

Would have to have enough trim to sync up to 15khz video

Certain extron boxes will convert analog to ttl but they do nothing to match frequency limits.

epictronics wrote on 2021-12-16, 21:14:

However, there are plenty of converters out there for all kinds of vintage systems.
Surely there must be something that could do it?

Too bad there converters mostly for the other direction. You can find multiple solutions to connect your IBM 5150 PC with an MDA card to a VGA or HDMI monitor (e.g. MCE2VGA, OSSC), but the other direction is rare. One exception is "TV out". You can find stuff to convert higher resolutions to NTSC TV timings (which by no accidence nearly identical to CGA timings). But the need to convert to uncommon timings, like MDA or hi-res EGA is so rare that I don't know of any available solution. Be careful: Most monitors, especially monitors using TV-inspired circuits, have an internal oscillator that controls the horizontal deflection. This internal oscillator is designed to be tunable only to frequencies the deflection can handle. If the HSYNC signal is out of range, synchronization just fails, but the deflection circuit runs at a frequency that the deflection circuit can handle. Not so on the IBM 5151. The HSYNC signal from video card drives the horizontal output transistor quasi directly. Bad timings can damage this monitor. It is specified for 18.4 kHz horizontal frequency. Probably it can handle 17.5 to 19.5 without any problems, but NTSC/CGA timing at 15.6kHz is outside of the acceptable range for a 5151, as is EGA timing at 21kHz.

Oh, crap, I just got my hopes up from the previous post.
I have my boards out for cleaning and there are five unlabeled pots that might adjust v/h hold/sync. I need to find the manual to confirm.

considering MDA is expecting TTL level signals, and VGA is analog.

Don't get your hopes up.

There were solutions for converting ega/vga to various TTL formats (common) without modifying frequency though the “phase” could usually be offset (ergo extron)

There are also common devices that cut the signal rate in half for CGA-Analog (also called Amiga, Targa or RGB-Sync) These are cheap because they just drop every other line.

but less common were scan converters because you needed “memory “ to do so.
The more obscure your conversion the more memory you needed.

That isn’t to say these didn’t exist, they certainly did but due to the $2000-$10000 price tag and the fact they targeted proprietary projectors (yes even B&W similar to MDA existed) and fixed frequency screens / medical Dental devices meant that they were
1. Low volume / used by institutional, CCTV networks and gov
2. Mostly dead by 1991
3. Usually inflexible in so far as the device they were converting to.

Finding such a device today that may have sold in the hundreds in 1982 would be challenging.

Don’t get me wrong many of us would have loved to be able to re-use the piles of discarded screens in the late 80’s and early 90’s due to the high cost of vga monitors
but nobody made anything affordable to hook a big standard vga card into one.

However there were a lot of screens that got hacked for vga, I owned a couple large fixed frequency screens that were internally modified for vga. I also had a real IBM 5151 that was board swapped by Jack Allen computers with a board from a severely burned Compaq mono vga and it could display VGA
Oddly that is likely easier than the converter.

weedeewee wrote on 2021-12-16, 22:47:

considering MDA is expecting TTL level signals, and VGA is analog.

Don't get your hopes up.

Converting to TTL is relatively simple compared to everything else mentioned, image appearance will be ass though

https://www.electro-tech-online.com/threads/h … l.111398/?amp=1

hmm.. Well, I expected this to be much easier but I guess I could swap the board if I can find a small enough mono VGA for a reasonable price.
There's only one on ebay at the moment and they are asking $125 🙁

Just get a late motherboard with an ISA slot. Then stick a mono/herc card in it and write a driver for a modern OS. 😀

I haven't tried in a long time, but Linux had support for mono displays. That might be your best option for something modern.

Scan converter is one thing, but...

there's also the question of software you're going to run on modern PC...
IBM 5151 can only display 350 scanlines, and 3 shades of gray.
Modern software is designed for much greater resolutions, and full color - so probably unusable on IBM 5151.
About all you can expect is 80x25 text console.

The 5151 is a wonderful TTL mono CRT. Do it justice by driving it with a real MDA/herc card on an ISA system please. Don't destroy the scanning drive in it by doing silly shit

Probably can't do too much harm to it if you do everything through a slow enough 74 series chip as a buffer. Then your modern GPU can be all "Ja, ich sprechen das TTL"

Oh, I have plenty of machines with proper MDA and Hercules that does my 5151's justice.
However, I want to have some fun playing around with them on different systems.

BitWrangler wrote on 2021-12-17, 04:18:

Probably can't do too much harm to it if you do everything through a slow enough 74 series chip as a buffer. Then your modern GPU can be all "Ja, ich sprechen das TTL"

did you miss the part where if you feed it a h-sync pulse outside an extremely narrow range around 18kHz it destroys itself?

Everybody should miss the part where they feed it h-sync out of range it sounds like.

What would be the application you'd use the 5151 that is different enough that requires a different system?

which part destroys itself when you feed it an out of range h-sync ?