VOGONS


First post, by keropi

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Hiya!

I was gifted an Acer 500+ XT setup and it has a CGA card , the setup is working fine but the composite colors are way off. First of all a picture of the card:

2qcffr8.jpg

It's a combo card as it also carries the FDD/IO controller and (maybe) an RTC (I assume that's the reason a BR2033 is there). It uses the 6845 crt controller, similar to the IBM cards AFAIK.

This is what I get in composite modes, left are pictures from the internet and right the picture I get:

6fcne0.jpg

19nq0z.jpg

and here is King's Quest 2 with pictures taken from GH's blog so this is the real deal (maybe the KQ1 pics are from there too, I just used google image search...)

148ozki.jpg

as you can see that's quite a difference... if anyone here has any idea of what to check and attempt to fix please do tell. Any extra info/tests are easy to do as well.

Thanks in advance for any help/tips!
😊

🎵 🎧 PCMIDI MPU , OrpheusII , Action Rewind , Megacard and 🎶GoldLib soundcard website

Reply 1 of 24, by Scali

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It's a common problem with CGA clones. Not much you can do about it, it's just a timing issue in the circuit (relative phase between color burst and pixel data).

http://scalibq.wordpress.com/just-keeping-it- … ro-programming/

Reply 2 of 24, by keropi

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oh man it's annoying 🤣
isn't there some info on how to fix this? It's a bummer for me since this card is unique to the machine I am using and can't be replaced easily... noone tried to fix that in clones? (my xt knowledge is very very limited...)

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Reply 4 of 24, by keropi

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^ excellent tip!

on my TV there is a TINT setting, didn't do much to improve this... but on the frameister the HUE setting does wonders 😀 , here is what I came up with after 1min of testing this:

29xad82.jpg

dbgmfp.jpg

it's not perfect but it is a huge improvement! Thanks StickByDos for this!

It would still be nice to fix this at hardware, surely someone in the past came up with a way to fix all these clone cgas...

🎵 🎧 PCMIDI MPU , OrpheusII , Action Rewind , Megacard and 🎶GoldLib soundcard website

Reply 5 of 24, by Scali

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Yea, most TVs don't have hue controls anymore. But it does exactly what you want: It rotates the phase of the colourburst. If you can adjust it far enough, you can fix the colours, because they're just shifted compared to real CGA. They are relatively correct, so to say.

I'm not sure if there ever was a fix. Composite CGA wasn't that common anymore by the time clones became commonplace. Most people probably just used them with RGBI. And back in those days (mid-to-late 80s), TVs and composite monitors probably still had hue controls, so you could fix it yourself.

http://scalibq.wordpress.com/just-keeping-it- … ro-programming/

Reply 6 of 24, by Great Hierophant

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Any CRT TV should have a Tint/Hue control, but the reason for a tint/hue control is due to the lack of error correction in NTSC color transmission. PAL TVs inherently include error correction which obviates the need for a tint/hue control. European TVs have a shaky compatibility with NTSC signals, so I am not surprised that the tint control on keropi's TV does little.

http://nerdlypleasures.blogspot.com/ - Nerdly Pleasures - My Retro Gaming, Computing & Tech Blog

Reply 7 of 24, by Gamecollector

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Great Hierophant wrote:

Any CRT TV should have

Any NTSC CRT TV.
PAL and SECAM are not "Newer the Same Color" ones. 😀

Asus P4P800 SE/Pentium4 3.2E/2 Gb DDR400B,
Radeon HD3850 Agp (Sapphire), Catalyst 14.4 (XpProSp3).
Voodoo2 12 MB SLI, Win2k drivers 1.02.00 (XpProSp3).

Reply 9 of 24, by keropi

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Well I did test with 2 14" sets that are NTSC-capable: a JVC unit and a Sony (one from the very latest crt models)
The JVC has TINT and the Sony has HUE settings. But both don't go so far as to actually fix the colors. So far I've only had success with the framemeister - but that's to be expected for the unit IMHO.
It's sad because the Sony set is so good that one can just use the pc from composite output. I will look inside the service menu just in case I can fix something there.

As for the 8088MPH I'd love to check it, where can I grab a copy?

edit:
I wonder, is there a schematic somewhere for a device that I can pass composite through it and change the hue with it and not from the display? It would be great if at least this solution existed...

🎵 🎧 PCMIDI MPU , OrpheusII , Action Rewind , Megacard and 🎶GoldLib soundcard website

Reply 11 of 24, by Great Hierophant

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Unfortunately, the TV's hue/tint control adjusts the relative phase of the color burst by only so many degrees toward the red or green. With my Tandy 1000 and IBM PCjr, I can sometimes get colors close to IBM CGA composite color with the tint control, but at other times I cannot no matter where the tint level is, similar to your results.

http://nerdlypleasures.blogspot.com/ - Nerdly Pleasures - My Retro Gaming, Computing & Tech Blog

Reply 12 of 24, by Scali

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Yes, the control is meant to fine-tune the setting, but in the case of CGA clones, they can be some 130 degrees off, which is way too much.

Reenigne developed a 'software' solution using the raw capture data from a capture device. This way you can get full control over the NTSC signal, and display it over a modern output such as VGA/DVI/HDMI/DP.
He used this 'software NTSC' for the capture of the final version of 8088 MPH that you can find on YouTube: https://youtu.be/hNRO7lno_DM

http://scalibq.wordpress.com/just-keeping-it- … ro-programming/

Reply 13 of 24, by keropi

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meh, software processing via another system... I can stick to the framemeister if I go that way 🤣
I posted on shmups forum, maybe someone knows of a color correcting circuit. Next and last attempt will be VCF , just so that I can put an end (or not!) to the quest.

🎵 🎧 PCMIDI MPU , OrpheusII , Action Rewind , Megacard and 🎶GoldLib soundcard website

Reply 14 of 24, by keropi

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allright here is something interesting... I downloaded CGACAL that is supposed to be a calibration program so you get proper cga colors. So I am getting these results, with NO hue/tint adjustments:

LCD:

WP_20150814_005_zpssc23czos.jpg

WP_20150814_007_zpsjzbqksw1.jpg

CRT (couldn't get a better photo, it looks too bright) :

WP_20150814_010_zpskeqdtzud.jpg

These look good, almost like the example pic on the CGACAL page (except BROWN ofcourse), correct? So why I am getting these results in games?!

WP_20150814_019_zps95jyzobo.jpg

RGB mode seems OK AFAIK:

WP_20150814_018_zpscxtkbz3x.jpg

what is going on here?

🎵 🎧 PCMIDI MPU , OrpheusII , Action Rewind , Megacard and 🎶GoldLib soundcard website

Reply 15 of 24, by Scali

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That is the problem with many clones: the composite output is calibrated for 16-colour textmode (the people making these clones weren't entirely inept, they DID try to make the composite output work to some extent).
It's only the graphics modes that are wrong (on some cards only mode 4, on others mode 6 is also 'wrong').
I have three theories on why this is:
1) Not many games used mode 4, because it is an undocumented way of abusing composite. Perhaps the designers of the hardware were not aware that composite should behave the same as IBM in this mode as well.
2) Tandy and PCjr also have a different phase from CGA. They may have deliberately tried to make the CGA clone match Tandy or PCjr, because more software for composite mode was designed for these systems than for regular CGA.
3) These cards tend to have extra features and modes (eg Hercules support, Plantronics etc). Perhaps it was too difficult/expensive to make it work correctly in all modes, so they dropped the least common modes.

http://scalibq.wordpress.com/just-keeping-it- … ro-programming/

Reply 16 of 24, by keropi

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I see... thanks for further explaining this , I begin to understand things a little better now.
So back at square 1 it seems - I thought I found something here 🤣 🤣 🤣

I did try KQ1 tandy/pcjr booters, they didn't work correctly with my XT, both had severe gfx errors and nothing even close to color 😵
I also found another utility specific for the systems CGA/combo board:

WP_20150814_003_zpsvntr42tg.jpg

it does support more modes... it switches between them just fine.

I'll continue to look for a solution...

🎵 🎧 PCMIDI MPU , OrpheusII , Action Rewind , Megacard and 🎶GoldLib soundcard website

Reply 17 of 24, by Scali

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I can do recordings of 8088 MPH on my ATi Small Wonder and Paradise PVC4 systems. I could also see if I can get King's Quest on there. You'll probably see some very familiar 'wrong' colours.
Trixter has done a capture of 8088 MPH on his PCjr, which also gave some interesting 'wrong' colours.

http://scalibq.wordpress.com/just-keeping-it- … ro-programming/

Reply 19 of 24, by Great Hierophant

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Scali wrote:
That is the problem with many clones: the composite output is calibrated for 16-colour textmode (the people making these clones […]
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That is the problem with many clones: the composite output is calibrated for 16-colour textmode (the people making these clones weren't entirely inept, they DID try to make the composite output work to some extent).
It's only the graphics modes that are wrong (on some cards only mode 4, on others mode 6 is also 'wrong').
I have three theories on why this is:
1) Not many games used mode 4, because it is an undocumented way of abusing composite. Perhaps the designers of the hardware were not aware that composite should behave the same as IBM in this mode as well.
2) Tandy and PCjr also have a different phase from CGA. They may have deliberately tried to make the CGA clone match Tandy or PCjr, because more software for composite mode was designed for these systems than for regular CGA.
3) These cards tend to have extra features and modes (eg Hercules support, Plantronics etc). Perhaps it was too difficult/expensive to make it work correctly in all modes, so they dropped the least common modes.

I think my blog entry http://nerdlypleasures.blogspot.com/2013/10/t … patibility.html dispels the idea that few games used mode 4 composite color graphics or that many games supported Tandy/PCjr composite color. I think that most clone manufacturers made sure that the direct colors would look OK and left it at that because increasingly fewer people were using composite color graphics.

http://nerdlypleasures.blogspot.com/ - Nerdly Pleasures - My Retro Gaming, Computing & Tech Blog