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CGA/EGA to VGA converters, are they any good?

L

Llamarama

Member
Joined
Jan 2, 2013
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24
Location
Tyneside
Hello everyone,

I've been looking for CGA and EGA monitors locally to no avail. However I have found some EGA/CGA to VGA converters cheap online. A few people in the classic arcade forums either love them or loath them saying they're great and useful or terrible with lag. All the ones i've seen appear to be the same unit, same blue board, same heatsink locations, same connectors in the same places, so i'm 90% sure there's just the one type.

I'm hoping to kill two birds with one stone with it, as I can then use my EGA IBM PC and CGA Amstrad PPC512/640. I don't plan on using them for high speed games, so a little lag is tolerable.

Has anyone on here used them or can offer any guidance on them?
 
The CGA/EGA-to-VGA-converter subject has been discussed many times previously in these forums.
To see those discussions, enter the following into the Google search box:
site:vintage-computer.com cga to vga converter
 
PeterLI said:
Plug in a VGA card and emulate MDA/CGA/HGA/EGA when so required. Good luck!
Click to expand...

NOT always an option though -- like when a system lacks expansion slots, has what few it has already full, or simply never had them in the first place.

See my Sharp PC7000, it's not like it has expansion slots... or a Tandy 1000 EX or HX which have non-standard connectors.

Most "converters" I've found the biggest problem is they are strictly 1 channel each of R, G and B -- so you are limited to 8 color instead of 16 or 64 color support. SOME of them though literally just wire those TTL outputs to the analog inputs, which is where I came up with my own solution of sorts...

for RGBI I put in diodes across the signal lines so as to not send back-signal, hooked the I line to each of the RGB lines with a pot in place to adjust the level of "I".

For rgbRGB I just put in two bit ladder DAC's across each, again with diodes just to be sure there was no back-talk.

Stuff so simple I was a bit surprised they didn't bother on most of these boards; they put all sorts of effort into making scan rates compatible, but nothing into actual color signal handling.
 
Last edited:
Thanks for the replies guys, I've got an NEC multisync LCD monitor, I know it's not the same and won't work right off the bat but the list of refresh rates it supports seems quite good, so I think i'll try some DAC designs and sync converters. Might need to double the sync frequency but I can always test it with trial and error. If possible i'd like to keep as close to original as possible, and money's a bit tight at the minute with christmas and those pesky relatives, so I can't really justify splashing out £30-40 on myself for a PC that may or may not work.

I tried using the built in search, but for some reason it keeps saying no matching criteria, even with wildcards thrown in.

I guess that's the trade off living over here, home computers for essentially nothing but business machines are virtually unobtainable (Unless it's an Acorn Archimedes).
 
As you are in the UK you can find TV/Monitors with SCART inputs which will sync to CGA frequencies so CGA to Scart is easy. EGA uses different scan rates so your mileage might vary, but many modern TV/Monitors will cope.
 
I've been looking into using SCART with a circuit similar to some of the CGA-SCART adapters posted here. The thing i'm most concerned with is the scan frequency, still, I have the chips needed to either double of half the frequency where needed, I'll have a bit of experimentation and will report back :)
 
PeterLI said:
Plug in a VGA card and emulate MDA/CGA/HGA/EGA when so required. Good luck!
Click to expand...

Sadly most VGA cards are not register compatible with CGA, they usually do not support the different CGA palettes, giving everything the black/while/purple/cyan look (the only card I've ever used that does support them is WD Paradise).
Also, VGA cards run their 320x200 mode at 70 Hz, while CGA/EGA run them at 60 Hz. So routines that depend on the raster timing will not work properly on VGA.
And I've never seen any VGA card that is Hercules-compatible.
 
Llamarama said:
I've been looking into using SCART with a circuit similar to some of the CGA-SCART adapters posted here. The thing i'm most concerned with is the scan frequency, still, I have the chips needed to either double of half the frequency where needed, I'll have a bit of experimentation and will report back :)
Click to expand...

CGA/EGA output a signal that has NTSC-compatible timings (60 fields per frame, 262 scanlines).
Most CGA cards and some EGA cards have an NTSC composite output, which you can connect directly to SCART.
If you don't have composite out, an RGBI->composite circuit is easy to build, it's basically just a set of resistors (some 14 of them I believe) and a transistor.
 
Ok most of you guys are talking over my head. From Scali it sounds as if maybe a Hercules adapter sounds good for me to obtain some color other than my IBM MDA solution. If I find a Hercules adapter what kind of monitor can I use with it? Is it possible to use a modern LCD or is the frequencies/scan rates and all that other stuff you tech guys are talking about that an LCD will not work with Hercules?

Thanks
 
Found this link somewhere.
https://www.youtube.com/watch?v=w1VPxhFlA2Q

Shows taking MDA output from the computer to a conversion box and then connects to a VGA monitor. This is interesting to me because it will allow me to preserve my own 5151 for as long as possible.

Getting ready to buy a vintage IBM VGA card but wanted this option. Speaking of vintage IBM VGA cards does anyone have a cable where pin 9 is solid? All my cables have all the 15 pins.

Thanks
 
stangman517 said:
From Scali it sounds as if maybe a Hercules adapter sounds good for me to obtain some color other than my IBM MDA solution.
Click to expand...

Erm, not sure what you mean, but the classic Hercules card is monochrome (although there is a rare InColor card: http://en.wikipedia.org/wiki/Hercules_InColor_Card). It's basically a modified MDA card, allowing graphics. It uses a standard MDA monitor. I think this rules out modern monitors. But it would allow you to get graphics on your MDA monitor.
You can also emulate CGA on Hercules.
 
The problem with the cheap converters is that they are designed for analog CGA, not TTL digital CGA, which is what PC compatibles use. Here's the only solution I've yet found that seems reasonable, and really does work (I bought one):

http://www.vintage-computer.com/vcforum/showthread.php?40965-Commodore-128-Video-DAC-Board-Available

I've not tried it on EGA...sounds like it will work in text modes or something, but not full graphics modes. Nice thing is it will of course work for any machine...and you don't lose the original compatibility as you would by using a VGA card - such as Tandy 16-color CGA modes.

Wesley
 
wesleyfurr said:
The problem with the cheap converters is that they are designed for analog CGA, not TTL digital CGA, which is what PC compatibles use.
Click to expand...

I think it's just false advertising really.
CGA *is* a PC-standard.
What they do is not CGA/EGA, but rather analog RGB, which is common in eg SCART signals for consoles, arcade machines etc.
By using the trimmers on these simple boxes, a digital RGB signal can be used as well... However, it is only RGB, there is no extra input for the intensity signals that CGA/EGA use.
I've seen some people using a special circuit to convert the digital RGBI output to an analog RGB, by using the intensity signal to modulate the digital RGB signals (and don't forget about that brown colour!).
If you do that, then you can use these 'CGA/EGA' to VGA converters properly.

There is also some small company that sells LCD monitors that have been modified to take digital RGBI signals. They probably use this circuit internally. You can find these monitors on Ebay, cost about 450 dollars I believe.
 
Ahhh, the joys of a MultiSync. MDA, CGA, EGA and VGA all in one unit. Fantastic picture, too. It's a really great monitor for its time.

I've still got one left if there's any interest.
 
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