Have you tried a CRT TV?

I second that idea, just give a CRT TV a try. 😀

Maybe also an old one in a wooden case, with RF jack.
A VCR or external video modulator can help to to interface that with your CGA.

Also, have a look at Great Hierophant's blog:
http://nerdlypleasures.blogspot.com/search/la … rtifact%20Color

It has a lot of information in regards of old video technology.

General speaking, good Commodore monitors -for example- were the Commodore 1701/1702 (original C64 monitor)
and the Commodore 1901/1902 (C128 monitor, Luma/Chroma, RGB; no composite ?).

By contast. the 1084 rather was meant as an Amiga monitor
(not *bad* either, but priority was on RGB, so not intended for artifacts).

Anyway, these are just my opinions. I'm from PAL lands, also.

aquishix since you are in the US just get a 1084 monitor that has both alalog and ttl RGB inputs. It will be PERFECT for your CGA needs. No need to worry about composite inputs, all 1084 models have it but not all support TLL RGB (it was used in Commodore PCs and the C128)
I use a 1084-S , both composite and ttl-rgb connected at the same time and the button on the front selects between them. It's just perfect.

ttl:

composite:

just in case anyone reads that in PAL lands like me - the 1084 NEEDS to be a NTSC version else composite will be b/w

Thanks for the pictures! 😀

Error 0x7CF wrote:

Have you tried a CRT TV?

Not yet, because up until a few days ago, I didn't have one anymore! I made an attempt to purchase a Sony Trinitron 20" 480i CRT TV back in February, and the idiotic seller did a poor packing job; it arrived completely busted and I got a full refund.

A little over a week ago, however, I purchased a Sony WEGA 36" 1080i CRT TV (which is also a Trinitron, of course) from a local seller that was offering local pickup only, for obvious reasons. I managed(with the help of two other strong men) to haul it upstairs to my 2nd floor game room, with much effort. Because it's up there, I've been a little hesitant to haul my IBM XT up there to test out the CGA card on it, but I probably will in the near future. (The XT has the case cover off and I've been doing various surgeries to it; it's not ready to be moved.) In any case, it's not an ideal place for a setup like that because that room is mostly dedicated to vintage console gaming and there's not a desk/table to put a keyboard and mouse on. So the most it would do for me to hook it up that way would be to verify that this CGA card properly outputs NTSC color artifacts. Hence why I'm trying to find a smaller CRT to use with my XT.

I have an "old style" CGA card and a "new style" CGA card, and I've already verified that both of them produce NTSC artifacts via the methods I mentioned in my original post. I just haven't witnessed the true glory of a CGA card, yet.

keropi wrote:

aquishix since you are in the US just get a 1084 monitor that has both alalog and ttl RGB inputs. It will be PERFECT for your CGA needs. No need to worry about composite inputs, all 1084 models have it but not all support TLL RGB (it was used in Commodore PCs and the C128)
I use a 1084-S , both composite and ttl-rgb connected at the same time and the button on the front selects between them. It's just perfect.

just in case anyone reads that in PAL lands like me - the 1084 NEEDS to be a NTSC version else composite will be b/w

You're always so helpful, keropi. =)

I'll do my best to get a 1084S at a reasonable price in the near future. They seem to sell well on eBay and the ones I was eyeing a few days ago appear to be gone.

Could the PAL/NTSC issue be the reason why the Amiga 1080 CRT strips the color out from my CGA's composite output? I've read some posts about how that particular model can handle PAL and NTSC.

Jo22 wrote:

I second that idea, just give a CRT TV a try. :) […]
Show full quote

I second that idea, just give a CRT TV a try. 😀

Maybe also an old one in a wooden case, with RF jack.
A VCR or external video modulator can help to to interface that with your CGA.

Also, have a look at Great Hierophant's blog:
http://nerdlypleasures.blogspot.com/search/la … rtifact%20Color

It has a lot of information in regards of old video technology.

General speaking, good Commodore monitors -for example- were the Commodore 1701/1702 (original C64 monitor)
and the Commodore 1901/1902 (C128 monitor, Luma/Chroma, RGB; no composite ?).

By contast. the 1084 rather was meant as an Amiga monitor
(not *bad* either, but priority was on RGB, so not intended for artifacts).

Anyway, these are just my opinions. I'm from PAL lands, also.

Very helpful as well; thank you! If I don't manage to get a 1084S, I'll go after one of the models you mention here.

And thank you for pointing me to The Great Hierophant's blog. I had already read his post(s) on this topic, but I appreciate it nonetheless. He has been an incredible resource for me over the last 8-9 months of my vintage gaming journey and everyone who is navigating this space needs to read his stuff. =)

Jo22 wrote:

By contast. the 1084 rather was meant as an Amiga monitor
(not *bad* either, but priority was on RGB, so not intended for artifacts).

Strictly speaking, the 1084 was made for the C128.
It was then modified to the 1084S, where the S means Stereo (and the Amiga also required analog RGB).
As keropi already said, as long as you have an NTSC model, a 1084 or 1084S will handle CGA artifacts just fine (and can also be used as TTL RGBI monitor).
The 1084/1084S was probably far more popular in the PAL world than in the NTSC world though.

The 1084/1084S are basically OEM versions of Philips CM8833 and related models, so looking for the original Philips (or perhaps another rebrand such as Magnavox, Aristona or Erres) could also do the trick.

Scali wrote:

Strictly speaking, the 1084 was made for the C128. It was then modified to the 1084S, where the S means Stereo (and the Amiga al […]
Show full quote

Jo22 wrote:

By contast. the 1084 rather was meant as an Amiga monitor
(not *bad* either, but priority was on RGB, so not intended for artifacts).

Strictly speaking, the 1084 was made for the C128.
It was then modified to the 1084S, where the S means Stereo (and the Amiga also required analog RGB).
As keropi already said, as long as you have an NTSC model, a 1084 or 1084S will handle CGA artifacts just fine (and can also be used as TTL RGBI monitor).
The 1084/1084S was probably far more popular in the PAL world than in the NTSC world though.

The 1084/1084S are basically OEM versions of Philips CM8833 and related models, so looking for the original Philips (or perhaps another rebrand such as Magnavox, Aristona or Erres) could also do the trick.

How about this one?

https://www.ebay.com/itm/MAGNAVOX-CM8502-074G … 872.m2749.l2649

aquishix wrote:

How about this one?

https://www.ebay.com/itm/MAGNAVOX-CM8502-074G … 872.m2749.l2649

It doesn't look bad to me. But I'm from PAL lands and only did a few tests with Composite CGA so far (on LCDs and multi norm CRT TV sets). 😀

@Scali Also thank you for the explanation! 😀
I've googled a bit and found some table with several Commodore monitors.
https://gona.mactar.hu/Commodore/monitor/Comm … del_number.html

Jo22 wrote:

It doesn't look bad to me. But I'm from PAL lands and only did a few tests with Composite CGA so far (on LCDs and multi norm CRT […]
Show full quote

aquishix wrote:

How about this one?

https://www.ebay.com/itm/MAGNAVOX-CM8502-074G … 872.m2749.l2649

It doesn't look bad to me. But I'm from PAL lands and only did a few tests with Composite CGA so far (on LCDs and multi norm CRT TV sets). 😀

@Scali Also thank you for the explanation! 😀
I've googled a bit and found some table with several Commodore monitors.
https://gona.mactar.hu/Commodore/monitor/Comm … del_number.html

...I am pleased to report that I received that Magnavox CM8502 CRT, and it works FANTASTICALLY! I could not be happier with it. For the first time in my life, I witnessed the glory of King's Quest I and II emitting CGA 16-color composite NTSC artifact-based graphics BEAUTIFULLY to a real CRT. Everything until now has been compromised in one way or another. The graphics are crisp, the text is clean, the colors are deep and bright...everything. Everything I've wanted in this corner of the vintage gaming space.

In fact, I'm tempted to say that it looks better with the composite output than it does with an EGA card. I'll post some pictures later for others to agree or disagree.

aquishix wrote:

...I am pleased to report that I received that Magnavox CM8502 CRT, and it works FANTASTICALLY! I could not be happier with it. For the first time in my life, I witnessed the glory of King's Quest I and II emitting CGA 16-color composite NTSC artifact-based graphics BEAUTIFULLY to a real CRT. Everything until now has been compromised in one way or another. The graphics are crisp, the text is clean, the colors are deep and bright...everything. Everything I've wanted in this corner of the vintage gaming space.

In fact, I'm tempted to say that it looks better with the composite output than it does with an EGA card. I'll post some pictures later for others to agree or disagree.

At least, that was what I witnessed when I plugged in my genuine IBM 5160 with a new-style CGA card.

Unfortunately, when I plug in my 10MHz XT Turbo clone, the image only displays in black and white despite what video mode it uses. I've tested many difference pieces of software, and that's always the case. I thought that pulling off the turbo jumper and forcing it back down to 4.77MHz would fix the problem, but it didn't.

I'm dismayed about this because it's throwing a monkey wrench into all my plans. I wanted, specifically, to use a 10MHz XT Turbo clone with a CGA card to play games like Kings Quest with CGA composite color artifacts.

Does anyone have any clue what might be going on here?

aquishix wrote:

Does anyone have any clue what might be going on here?

The original IBM 5150 and 5160 have an adjustable capacitor on the motherboard, which can be used to fine-tune the clockspeed. IBM added this because the CGA card uses the motherboard clock to generate the video signal, and the NTSC colour signal is very sensitive.

Most clones do not appear to have this adjuster, in which case you're relying on pure luck whether or not the NTSC signal will be accurate enough for your display.
It could be that your clone's clock is too far off, resulting in the monitor not picking up the NTSC colorburst properly.
If there is no adjuster, I suppose the only thing you could try is to replace the crystal on the motherboard, and hope you get lucky with one that matches your display.
Having said that, I assume that you did manage to get colour composite from the clone with other displays? (Not sure if you used the IBM CGA card in the clone, or some clone card).

Scali wrote:

The original IBM 5150 and 5160 have an adjustable capacitor on the motherboard, which can be used to fine-tune the clockspeed. I […]
Show full quote

aquishix wrote:

Does anyone have any clue what might be going on here?

The original IBM 5150 and 5160 have an adjustable capacitor on the motherboard, which can be used to fine-tune the clockspeed. IBM added this because the CGA card uses the motherboard clock to generate the video signal, and the NTSC colour signal is very sensitive.

Most clones do not appear to have this adjuster, in which case you're relying on pure luck whether or not the NTSC signal will be accurate enough for your display.
It could be that your clone's clock is too far off, resulting in the monitor not picking up the NTSC colorburst properly.
If there is no adjuster, I suppose the only thing you could try is to replace the crystal on the motherboard, and hope you get lucky with one that matches your display.
Having said that, I assume that you did manage to get colour composite from the clone with other displays? (Not sure if you used the IBM CGA card in the clone, or some clone card).

I have two genuine IBM CGA cards -- one old-style and one new-style. No other CGA cards. Both of them produce the same black and white images when plugged into this XT Turbo clone.

However, the same XT Turbo system outputs NTSC color artifacts just fine(with either CGA card) when adapted through the Startech composite -> VGA adapter I mentioned earlier in this thread. That's why I was shocked to discover this problem using a genuine color composite monitor.

Scali, please say would it be possible to install a bog standard ~3,58 MHz (3.579545 MHz) crystal oscillator directly on such an IBM CGA card ?
I have no genuine CGA card at hand for testing this, so perhaps this is just a foolish idea, but from what I read on the net, IBM's CGA card
was said to have had unnecessarily derived the NTSC signal from the PC/XT bus..

Jo22 wrote:

Scali, please say would it be possible to install a bog standard ~3,58 MHz (3.579545 MHz) crystal oscillator directly on such an IBM CGA card ?

Pretty sure it's possible (although it'd probably have to be a 14.32 MHz bog standard NTSC crystal). Just cut the trace to pin B30 on the ISA bus, and connect your own clock generator circuit there:
http://old.pinouts.ru/Slots/ISA_pinout.shtml

However...

Jo22 wrote:

but from what I read on the net, IBM's CGA card was said to have had unnecessarily derived the NTSC signal from the PC/XT bus..

Whoever said that, has no idea what IBM did, or was trying to do with CGA.
Why is the clock speed of their PC 4.77 MHz? The original 8088 was specced at 5 MHz, so why did they not just run at the full 5 MHz?
NTSC, that is why. 4.77 MHz is exactly 14.32/3. So they derived the clock speed from an NTSC base clock, by dividing it by 3. That is why the PC runs at that strange speed of 4.77 MHz (and early clones would have a turbo at 14.32/3 = 7.16 MHz or 14.32/2 = 9.54 MHz).

If they hadn't done that, 8088 MPH would never have been possible (and if you would modify a CGA card with your own oscillator, it would also break 8088 MPH compatibility).
The reason is that the entire system runs on a single clock, and that means that everything is in sync. The CPU, the chipset timer, the ISA bus, and the CGA card.
This means that you can count CPU cycles or PIT cycles and relate them directly to the display.
Most machines from the late 70s and early 80s work like that (that's why they all have weird speeds like 0.985 MHz and such, derived from PAL or NTSC base clocks, to synchronize the entire system to the display). In fact, the Atari VCS and ZX81 rely on it to generate a display at all: their chipsets are so primitive, that you need cycle-exact timed CPU writes to generate a display.

So if you were to modify something, I wouldn't modify the CGA card. I would modify the circuit on the motherboard that generates the OSC signal on pin B30. If you could add a trimmer to that, like the original IBM PCs have, then you can fine-tune the clockspeed to get the NTSC signal correct.

Scali wrote:

The original IBM 5150 and 5160 have an adjustable capacitor on the motherboard, which can be used to fine-tune the clockspeed. I […]
Show full quote

aquishix wrote:

Does anyone have any clue what might be going on here?

The original IBM 5150 and 5160 have an adjustable capacitor on the motherboard, which can be used to fine-tune the clockspeed. IBM added this because the CGA card uses the motherboard clock to generate the video signal, and the NTSC colour signal is very sensitive.

Most clones do not appear to have this adjuster, in which case you're relying on pure luck whether or not the NTSC signal will be accurate enough for your display.
It could be that your clone's clock is too far off, resulting in the monitor not picking up the NTSC colorburst properly.
If there is no adjuster, I suppose the only thing you could try is to replace the crystal on the motherboard, and hope you get lucky with one that matches your display.
Having said that, I assume that you did manage to get colour composite from the clone with other displays? (Not sure if you used the IBM CGA card in the clone, or some clone card).

I am pleased to report that my clone motherboard actually DOES have an adjustable capacitor on the back near the 8-bit bus slots. I adjusted it while the system was on and outputting CGA graphics and the colors immediately came through on my composite monitor. Epic win!

In addition to that, the (busted) motherboard I had just extracted from my XT Turbo clone case also has an adjustable capacitor at the back of the case which I assume is for the same purpose. If they're really not common, I must've lucked out...twice.

Also, this 3rd XT clone motherboard I've got does NOT have an adjustable capacitor on it, but my D421000 DRAM chips finally came in the mail, and when I plugged them in I was happy to discover that the clock tuning on that particular motherboard is great for composite NTSC color artifacting. So, I now have at least two options that are serviceable. I'm going to try both of them on my Startech composite->VGA adapter and on my Magnavox composite monitor to see what the best matching of hardware is.

Thank you very much! You helped end a dreary chapter in my retro/vintage computing life.

aquishix wrote:

I am pleased to report that my clone motherboard actually DOES have an adjustable capacitor on the back near the 8-bit bus slots. I adjusted it while the system was on and outputting CGA graphics and the colors immediately came through on my composite monitor. Epic win!

Great that you could get it working!

aquishix wrote:

If they're really not common, I must've lucked out...twice.

Yea, I'm not sure about numbers exactly, but back in the day I mostly saw OEM clones from brands like Tulip, Philips, Commodore, Atari etc. And they didn't seem to have them.
Mind you, these were of a later generation, 1987 and beyond.
I suppose in another market, it may have been more common. I am thinking of the market of replacement/turbo boards designed to be retrofitted into an IBM 5150 or 5160. These would have to have the same form factor as the IBM board, and perhaps then it's obvious to also put the adjuster on there.

It could also be that by the late 80s, it was no longer seen as a requirement, because parts were stable enough anyway that NTSC always worked.
In fact, I don't know if any other machines with NTSC output ever had such an adjuster. I don't think a Commodore 64 has one, for example.
I don't even think IBM's PCjr has it (edit: seems it does, on the left bottom, next to the oscillator: https://bunniestudios.com/blog/images/ntw_nov_2012.jpg)
My IBM 5160 has one, but I never touched it. It worked fine when I got it.

In retrospect these adjusters may have done more bad than good: I have a Philips clone and a Commodore clone, neither has an adjuster, and both work fine.
It could be that these adjusters get knocked out of alignment over time, especially when computers get disassembled, boards get stored, shipped etc.