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MDA / CGA / EGA

maelstrm

maelstrm

Experienced Member
Joined
Jun 6, 2022
Messages
99
Location
Raleigh, NC
Hello Federation,

I have a few questions regarding MDA / CGA / EGA cards and monitors. I'm soon going to receive an IBM 5153 monitor and want to make sure I connect it safely. I have (what I think is) an EGA card. Just want to make sure of a few things:

  • Is it safe to connect the 5153 (a CGA class monitor) to an EGA card?
  • Am I correct in understanding that connecting an MDA card to a 5153 or 5154 could damage the monitor?
  • Can anyone confirm that the card below is an EGA card. FCC ID is E5Y6L9MG-150 / Model (?) ET-1000 Rev. 1D. I did mistakenly (but very briefly) connect the below card to an MDA monitor. I saw it was out of sync and immediately removed the cable. Luckily no damage.


    Video_Card_Beger_EGA_et1000.jpg
And I'm almost certain this one is CGA. Thas a 9-pin out and a composite connector:

1501981_CGA_Video_Card.jpg

Just want to make sure of everything before I blow something up.
 
The first card says MG-150, so it’s probably a DFI MG-150 which is monochrome graphics.

EDIT: Turns out I had the manual for that one. Attached is a scanned copy. As always, if I post an old manual that I've scanned here, anyone that wishes can choose to archive it.
 

Attachments

  • DFI MG-150.pdf
    6.7 MB · Views: 19
Last edited:
jafir said:
The first card says MG-150, so it’s probably a DFI MG-150 which is monochrome graphics.

EDIT: Turns out I had the manual for that one. Attached is a scanned copy. As always, if I post an old manual that I've scanned here, anyone that wishes can choose to archive it.
Click to expand...
Wow thank you!!
 
You're most likely to damage hooking a monochrome (MDA) monitor to a CGA or EGA card. The reason is that most MDA-type monitors don't have a horizontal oscillator per se, but rather depend on the horizontal sync pulses to generate the sweep necessary. The casualty is usually the flyback transformer or horizontal output transistor.

A CGA or EGA type monitor does have a horizontal oscillator and will usually display an out-of-sync image, but not harm the monitor itself.
 
+1 to the above, at least for the original IBM 5151 mono monitor and similar; the "hsync" output from the MDA is used as a direct drive signal instead of a synchronization source.

(FWIW, I'm pretty sure some third-party MDA monitors do have a full sync setup, especially the "dual mode" monitors which could handle both MDA and CGA in monochrome; early example of this is the Princeton Graphics MAX-12, but this capability wasn't terribly uncommon generally in TTL mono monitors near the end of their market lives.)

As for hooking a 5153 to an EGA card, EGA cards generally have DIP switches on them to set their default text mode to the CGA-compatible 200 line mode instead of the 350 line mode. You need to set that or you won't be able to read the text at boot. For that matter there's also a switch setting to hook an MDA monitor up to an EGA card, but unless you have an enhanced card like an ATI EGA Wonder it's mostly useless. (Only gives you one monochrome graphics mode that's like Hercules in 2-bit grayscale but not compatible with it, very little software supports it. This combo won't do any other EGA graphics mode.)
 
maelstrm said:
And I'm almost certain this one is CGA. Thas a 9-pin out and a composite connector:
Click to expand...
IBM's CGA card. See [here].

jafir said:
EDIT: Turns out I had the manual for that one. Attached is a scanned copy. As always, if I post an old manual that I've scanned here, anyone that wishes can choose to archive it.
Click to expand...
Thanks. I have added it to [here].
 
Confirmed this MG-150 is an MDA adapater.

Unfortunately I think this one has some issues. After a few minutes of use, random characters begin to appear on the screen in various places. I'm suspecting faulty RAM on the card. The issue doesn't occur when using another MDA card.

Thanks all for the info!
 
Technically, the MG-150 is a monochrome graphic adapter (MGA, hence the "MG" in the part number). Often referred to as "Hercules Graphics compatible". The bulk of the Far East-manufactured monochrome cards were this type, as ERSO made the design available to its vendors and the production price wasn't much different from a plain text-only MDA.
 
Chuck(G) said:
Technically, the MG-150 is a monochrome graphic adapter (MGA, hence the "MG" in the part number). Often referred to as "Hercules Graphics compatible". The bulk of the Far East-manufactured monochrome cards were this type, as ERSO made the design available to its vendors and the production price wasn't much different from a plain text-only MDA.
Click to expand...
Thanks that's good to know. I was wondering why the manual was making mention of EGA.
 
Despite being warned about it for the past 40 years, I've never seen any proof of actual damage caused by plugging an MDA monitor into a CGA card or vice versa. Just like the Commodore PET "smoke POKE", it has some kernel (kernal?) of truth, but is mostly an overblown myth.

In fact, maybe it's built unusually well, but my Tandy CM-11 CGA monitor suffers no ill effects when displaying MDA/Hercules video, even for extended lengths of time. Of course I have to adjust the controls to compensate for the different horizontal and vertical frequencies, and even with the size controls set to their minimum the image gets cut off, but otherwise absolutely no harm is done. (This is with a Tandy 1000RL which outputs MDA video on the color green pin 4 as well as the dedicated monochrome video pin 7; if I had used a regular MDA card which only outputs video on pin 7, I wouldn't get an image on the monitor.)

mda_on_cga1.jpgmda_on_cga2.jpg

And as for the opposite -- trying to display CGA on an MDA monitor -- you'd be running it at less than its normal scanning frequency, so I fail to understand how that could damage it. You'd be understressing the circuitry, not overstressing it.
 
vwestlife said:
And as for the opposite -- trying to display CGA on an MDA monitor -- you'd be running it at less than its normal scanning frequency, so I fail to understand how that could damage it. You'd be understressing the circuitry, not overstressing it.
Click to expand...

Here's a StackExchange thread that talks about the operative theory. Long and short of it is the circuitry in the 5151 is "tuned" to run at a particular duty cycle and running it too slow will cause it to overheat/experience excessive voltage spikes. There seems to be plenty of anecdotal evidence that it's at least possible to nuke a 5151...

That said, I wonder how many mono monitors are actually clones of the 5151. My gut feeling is many if not most third party ones have a real sync circuit and *don't* use the same direct-drive system as the 5151. Monitors like that should just lose sync instead of nuking themselves.

As for the CM-11 syncing with MDA... I guess that's impressive that particular monitor will sync over such a wide range, but I think that's kind of atypical.
 
I can speak from experience. I toasted two mono monitors back in the 80s through pure programming errors (did you think that SIMCGA worked the first time?). In both cases, it was the flyback transformer that went poof. Said monitors were Taiiwanese clones (14" amber phosphor) of the 5151.
 
Software publishers, yes; I don't believe that card manufacturers were part of the picture, however. I could be mistaken--after all, this was some 35 years ago....
 
Chuck(G) said:
I can speak from experience. I toasted two mono monitors back in the 80s through pure programming errors (did you think that SIMCGA worked the first time?). In both cases, it was the flyback transformer that went poof. Said monitors were Taiiwanese clones (14" amber phosphor) of the 5151.
Click to expand...
Some LGR youtube video about the herc graphics came through my screen on autoplay the other day. I was only halfway paying attention but I looked at it just in time to see the sydex sign on text of him using that utility. I was like "hey I know that guy"
 
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