Quick help with Converting monochrome CRT db9 to LCD db15?? signal?

[fastline]

I lost a crt monitor on a machine and need it back up soon. I really figured I could just fab up a db9 to db15 cable realizing I won't obviously get color without a color card, and move on with life.

I cannot find a clear cable pinout and it seems I might have further signal issues. Can someone guide me on this?

 

[jbeng]

Check the link below. It may help. Or not.

https://what-when-how.com/display-i...-personal-computer-display-interfaces-part-1/

 

[fastline]

Yes, and if I have understood the reading correctly, the output I likely have is MGA/CGA/EGA which is a TTL level output meaning it is sort of digital. However, what my monitor needs is VGA which is analog wave form?? So I need a special converter to do this?

Actually, since this CRT is monochrome (no color), it is nearly guaranteed to be MGA, correct?

 

[ronsimpson]

Ground to ground
H sync to H sync
V sync to V sync
-------hard part--------
TTL video to analog video (Green) Probably will work but the signal might be too strong. Picture will be green if you can live with that.
---or---
TTL video to analog video RED,GREEN,BLUE. By connecting all three wires together the TTL signal will be loaded down. White picture.
--or--
I remember using a voltage divider to drop the TTL level down to 0.7 volts for the analog level. This will take some playing around. Example two 75 ohm resistors make a 2:1 divider.

 

[fastline]

Ron, I appreciate it. One of the concerns or goals is to at least get resolution. I am told the primary issue is the refresh rate from the old CRT is 15khz and about the lowest one of the more modern LCDs will take is 30 khz.

Are there simple ways to work around this issue?

I have stumbled into some cheaper converters that will work wtih cga/ega input which is also ttl, and output VGA. I am hoping that if nothing else, I can find a way to use them for this. I am hopeful if they can do full color ttl level, they should do monochrome IMO. inputs on those are r, g, b, h, v, g. Not sure if I would get a better image? I think they up scan to 30khz but cannot confirm.

 

[ronsimpson]

The old CRT ran at 15750 by 60. So it is "TV" like.
VGA will not work because it will not go below 32khz.
You need a TV. There are some old LCD TV sets that might work.

 

[fastline]

Are you saying 15.7khz x 60hz vert? Looking at a replacement unit, they spec it at 49.7hz vert.

I am interested in either line conditioning or converting the signal. Curious what site might be best to discuss this? Being only monochrome, I would hope this would simplify the design? The upscanning is what I have issue with. 15khz needs to be more like 30-40khz. I think I can use simple series resistors to get the TTL down to tolerable for a LCD.

The main issue is even a TV is not going to operate at the right frequencies?? How do you arrive at a TV fixing this issue?

 

[ronsimpson]

Most TVs will do 49.7hz or at least 50hz.
You should look at the Vsync and see what frequency it is really. 50hz is slow and causes some flicker.
A monitor might say 49.7 to 80hz vertically.

15750 is old TV. 15k is 15750. I have a LCD TV and it will operate at 15k x 49hz. Most TVs need composite video. You need a TV with "computer video" in.

I also have a Zenith L15V26C that works at 15750 x 60 and (30khz through 60khz) x (60 through 85). I could test it at any resolution. I do have a way of making any video format. I think it will work form 15k through 60khz) The TV/monitor has many different inputs.

You do not want to make a scan converter. You might be able to get a TV to VGA converter. All I know of double the H. rate. 15750 to 31500 and do not change the vertical rate at all.

 

[fastline]

Well, the issue here is we have to have a specific screen size, which is hard enough to find, then try to find one with the right db9 input? I know there were some "multisync" monitors that had this input but they are now going for huge dollars due to new uses.

I can examine the vid source signal as long as there is no concerns of damage? We are looking at hundreds of dollars for repair if that happens.

What really needs to happen is a simple way to get this old mga signal to a modern monitor. There are several reasons for it. We have more than one, concerns if the lcd goes out and we cannot just grab something to get going, and sourcing some old hardware.

Can we not throw something together on a project board? Going to require a microcontroller to get it done?

 

[fastline]

Ron, I am refreshing this thread as I am revisiting this issue in connecting a modern VGA input LCD to an archaic MDA TTL signal. I have dug up the specs for the CRT but need to determine the feasibility here. You mentioned tying the RGB together to the TTL vid signal but I am mostly wondering about refresh rates and such.

I am not terribly picky about the image and such but a very annoying flicker will hurt eyes after a while. There are some specific industrial converters out there to convert the TTL to VGA analog but not sure if they would really produce a better image?

So are the refresh rates determined only by the monitor? What are my options?


Here is the original monitor spec.

CRT size . . . . . . . . . . . . . 12"
Phosphor . . . . . . . . . . . . Amber or page white
Scanning . . . . . . . . . . . . non-interlaced
Horizontal freq . . . . . . . . . 18.18 Khz
Vertical freq . . . . . . . . . . 50 Hz
Video Response . . . . . . . to 22 MHz Max
Resolution . . . . . . . . . . . . 720 X 400
Signal type . . . . . . . . . . . . Separate TTL

 

[tunedwolf]

Ebay has loads of listings for small 12" mono monitors with a mix of MDA/EGA/CGA if you're stuck for a monitor. One other possibility might be looking at old, but well regarded, security monitors. As loads of them also had EGA etc inputs on them as well as composite inputs. It may actually be easier to get your hands on a more up to date graphics card that will run with your equipment, and then update your screens because none of the solutions you are going to find are any sort of long term fix/ plan.

 

[fastline]

There seems to be one such converter box that specifically converts the ttl signals to VGA. I just wanted to make sure there were no easy outs. The box is not cheap but not terribly expensive either when you consider any other upgrades. My goal is nothing short of an LCD.

Unfortunately, the designers of the CNC control integrated the vid outputs into the main processor board so of course they can "upgrade me" but thousands of dollars later. Not going that route.

 

[ronsimpson]

Please give us the information on the converter box. Where?

 

[fastline]

**broken link removed**

Here is a link to a manual. I did check and they support ttl signal.

 

[ronsimpson]

Thanks, that should work.