How to add CVBS-output to an ATI SMALL WONDER that omits it (instructions inside)

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How to add CVBS-output to an ATI SMALL WONDER that omits it (instructions inside)

Postby keropi » 2018-7-21 @ 17:32

Hiya

I was given an ATI SMALL WONDER GRAPHICS SOLUTION Version 1 card but it was a revision that was missing the composite output. Since I had a dead card but with the CVBS output installed I decided to add the missing components to the working one and see what happens. It works :lol: but naturally the cvbs colors do not match the IBM CGA so they are wrong in games. Still better than nothing though :cool:

So this is a list of what you need to add in case someone wants to do the same:

Image
(image taken from the awesome VGA LEGACY MKIII website)

R1: 1.1 kΩ
R2: 2.2 kΩ
R3: 3.3 kΩ
R4: 750 Ω
R5: 750 Ω
R7: 680 Ω
R8: 750 Ω
R9: 360 Ω
R10: 75 Ω
R11: 33 Ω
C15: 150 pF
Q1: 2N3904
P2: RCA connector
J2: 4pin header (internal cvbs header for use with the IBM portable , pin2 is not populated)

You might also want to jumper JP2 as shown in the picture - I have no idea what JP1/JP2/JP3 do but the card with composite had this jumper installed.

That's it. It works but like I said the CVBS colors are wrong, if the target monitor has TINT controls then you can fix them on the monitor side.
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Re: How to add CVBS-output to an ATI SMALL WONDER that omits it (instructions inside)

Postby Deksor » 2019-11-03 @ 00:20

I'm bumping this thread because I have two Small Wonder with the same component layout as yours, except mine have the included composite output :confused:

Are my composite outputs useless ? Monochrome only ? And is there any hardware fix for the bad colors in composite mode ?
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Re: How to add CVBS-output to an ATI SMALL WONDER that omits it (instructions inside)

Postby Benedikt » 2019-11-05 @ 20:07

If your Small Wonder cards are fully populated, the composite output is most certainly not useless.

Mine looks like this:
ATI_GS_front.jpg

IIRC the 80x25 text mode is monochrome, only, much like on a real CGA, except that the color burst is is most likely completely absent rather than just too short.

I don't think there's an easy fix for the "wrong" artifact colors and if there was, it would then mess up the real (i.e. intentional, non-artifact) colors.
It does not bother me too much, because I'm not going to get colors on a PAL screen, anyway.
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Re: How to add CVBS-output to an ATI SMALL WONDER that omits it (instructions inside)

Postby Jo22 » 2019-11-07 @ 00:48

Benedikt wrote:It does not bother me too much, because I'm not going to get colors on a PAL screen, anyway.

Why not ?, if I may ask. :) Unless the PAL screen in question is a real vintage piece (Commodore 1702 video monitor etc),
the NTSC/60Hz stuff should work via CVBS (FBAS), too. Personally, I had success with several little CRT TVs from
"Sperrmüll" and with older, bigger CRT TVs (Sony, Sharp) from circa late 90s to mid-2000s.
The usual LCDs and TFTs with Composite/CVBS inputs are sold all around the world and multi-standard thus.
Just a few years ago I tested one oddball CGA card with one (Philips 15PF4121), for example (viewtopic.php?p=499836#p499836).
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Re: How to add CVBS-output to an ATI SMALL WONDER that omits it (instructions inside)

Postby Benedikt » 2019-11-07 @ 14:11

Jo22 wrote:Why not ?, if I may ask. :) Unless the PAL screen in question is a real vintage piece (Commodore 1702 video monitor etc),
the NTSC/60Hz stuff should work via CVBS (FBAS), too. […]

I'm using it with a Commodore 1084. It does support 50Hz and 60Hz, but the CVBS input is PAL-only, meaning that I can only choose between RGBI and grayscale composite.
The latter is only really useful for CGA mode 5, the graphics mode that is supposed to have four shades of gray but displays in color on an RGBI screen.
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Re: How to add CVBS-output to an ATI SMALL WONDER that omits it (instructions inside)

Postby keropi » 2019-11-07 @ 14:33

^ yes sadly this is true for the 1084... at one point I looked into NTSC conversion but it requires some weird parts to do it IIRC
I lucked out and actually found a NTSC model locally - perfect companion for CGA because you can use a single monitor for TTL and CVBS modes:

Image Image
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Re: How to add CVBS-output to an ATI SMALL WONDER that omits it (instructions inside)

Postby Deksor » 2019-11-09 @ 19:13

Here's how the two I have look like :
Image

As you can see, the composite output is populated (and rusty, but that's another problem :lol:). I haven't tried them now, but since I live in europe (and in a place with SECAM and not PAL), I suspect the circuit can only do black and white at the moment.

I have some sony trinitrons that support NTSC okay iirc, so I could test that.
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Re: How to add CVBS-output to an ATI SMALL WONDER that omits it (instructions inside)

Postby Benedikt » 2019-11-09 @ 21:10

Interesting.
There are ten resistors, a capacitor, a pin-header and a transistor missing, but the output connector is there. Maybe that does indeed mean that your cards are monochrome-only or maybe even that the connector is just a decorative gap filler.

You should definitely test that at some point. In any case, you can still follow keropi's instructions to fully populate the board. My photo can serve as visual reference.
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Re: How to add CVBS-output to an ATI SMALL WONDER that omits it (instructions inside)

Postby Jo22 » 2019-11-10 @ 01:18

Benedikt wrote:Interesting.
There are ten resistors, a capacitor, a pin-header and a transistor missing, but the output connector is there. Maybe that does indeed mean that your cards are monochrome-only or maybe even that the connector is just a decorative gap filler.

You should definitely test that at some point. In any case, you can still follow keropi's instructions to fully populate the board. My photo can serve as visual reference.

Hi! :)That transistor.. What kind might it be ?
I think I remember that some simple CGA-SCART circuit used a field-effect type to combine H/V sync signals into one.
Or maybe the card needs it to combine luma/chroma into one, as well, to create a final CVBS/Composite signal.
Or perhaps it has to do with the color burst stuff that NTSC needs, dunno.

Forgive my ignorance. :blush: I both like and "hate" CGA a lot (wrote some simple utilities for it), but Composite CGA, in color, is beyond me,
since I grew up in the PAL lands and my old TV books and technical magazines don't cover NTSC in great detail.
Also, I'm using CGA currently mainly on a green monitor with an XT class machine that has CGA in mono on its RCA output..
On such a setup, CGA looks quite well and has the nice side effect of leaving more DOS memory left for the user.
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Re: How to add CVBS-output to an ATI SMALL WONDER that omits it (instructions inside)

Postby Benedikt » 2019-11-10 @ 10:06

Jo22 wrote:Hi! :)That transistor.. What kind might it be ?

Keropi lists it as 2N3904. That would be a general purpose NPN transistor.
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