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soviet9922
September 24th, 2017, 05:00 PM
I have seen a lot of different schematics for cga ttl to - analog rgb scart adapters.

Found that this one is recommended:
http://static.elitesecurity.org/uploads/1/9/1908877/CGA%20TO%20SCART.jpg

I see that pin 7 on the cga port is marked as 5+ but on pinouts of the port says (reserved) or (ttl video).
Somebody knows more about this adapter, or that is is safe to use this schematic ?.

Thanks!.

David_M
September 24th, 2017, 06:49 PM
The standard is for pin 7 on the CGA to be not connected, however some cards are dual CGA and MGA. On those cards pin 7 is the mono video signal.
The is enough resistance in the schematic to not harm the video output of a mono card and a CGA that has no connection on pin 7 wont be harmed either.
The lack of 5v being output by the video card means the circuit wont work. You will need to get a non switchable CGA video card that has no connection on pin 7 and connect it to a 5V source on the card.

Trixter
September 25th, 2017, 09:08 AM
That adapter will produce an incorrect color for #6 (brown); it will show up as light yellow. Otherwise it seems ok.

Why is #6 brown? Answer (http://www.oldskool.org/pc/cgacal).

soviet9922
September 25th, 2017, 09:37 AM
Thanks, for the reply's guys also joining together the sync signals using resistors is not an AC short ?

Retro Canada
September 25th, 2017, 11:37 AM
It has resistors, they are protected and attenuated.

The transistor is just converting the signals to negative composed sync, but it won't be a serrated vsync. But the scart 2 hdmi doesn't care about it.

It might work but just using a XNOR gate between H and V and adding a 470 ohm resistor at the output.

The brown color could be fixed by adding decoders. If we had a fast EPROM (10ns) that would be simple, but they are damn slow. Maybe a GAL ?

RobertK
October 3rd, 2017, 06:51 AM
See here (http://www.vcfed.org/forum/showthread.php?17610-CGA-to-SCART-adaptor&p=452967#post452967). I have named the three different schematics variants "1 to 3" (this one is variant 1), there is even a fourth variant. There you can read my explanation for your pin 7 question.
Note that the Green signal should be connected to SCART pin 11 instead of 4, this was an error in this diagram.

I can say that I have built variant 3 and it works perfectly (without brown-fix however, but I don't really need that), see my pictures over there.

Trixter
October 3rd, 2017, 07:05 AM
(without brown-fix however, but I don't really need that)

Why don't you need the brown fix?

RobertK
October 3rd, 2017, 07:26 AM
Why don't you need the brown fix?
Because most of the games I play use either one of the two standard CGA palettes, or cyan, red & white (which was also quite popular among game developers and good-looking IMHO). None of these are affected by the brown problem.

But there is actually one CGA game where I would like to have the correct brown color displayed: Defender of the Crown (CGA). It still looks good without the brown fix, but of course it's not the real thing.

Ok, Paku Paku (http://deathshadow.com/pakuPaku) also uses the brown color, but I don't mind seeing dark yellow instead of brown, the game is still great anyway!

soviet9922
October 14th, 2017, 01:00 PM
Because most of the games I play use either one of the two standard CGA palettes, or cyan, red & white (which was also quite popular among game developers and good-looking IMHO). None of these are affected by the brown problem.

But there is actually one CGA game where I would like to have the correct brown color displayed: Defender of the Crown (CGA). It still looks good without the brown fix, but of course it's not the real thing.

Ok, Paku Paku (http://deathshadow.com/pakuPaku) also uses the brown color, but I don't mind seeing dark yellow instead of brown, the game is still great anyway!

Thanks for the link, i don't whant care for the brown color going to build one you provided in the shematic.
the only problem i see is that i have an original brown cga card from ibm, i don't think theres a signal on pin 7 to feed power to the transistor.
Maybe i have to add a separated power supply for it a cellphone one that provide 5v?

ibmapc
October 15th, 2017, 11:12 AM
... i don't think theres a signal on pin 7 to feed power to the transistor.
Maybe i have to add a separated power supply for it a cellphone one that provide 5v?
You should be able get 5v from the ISA Bus pin B3. See Here (http://pinouts.ru/Slots/ISA_pinout.shtml) Preferably, trace to a point on the card that can easily be soldered to and run a wire from there to the pin 7 on the connector as long as it is NC. If necessary, you can solder to the finger of the edge connector, but be careful not to let the solder get to far down on the finger so that it doesn't get into the ISA connector when the card is plugged in. You may need to cut a trace if pin 7 is connected. I don't have the schematic in front of me for the IBM CGA card but it should be easy enough to check visually or with a meter.

I believe this is what David_M indicated when he said "You will need to get a non switchable CGA video card that has no connection on pin 7 and connect it to a 5V source on the card." in post #2.

Retro Canada
October 15th, 2017, 11:31 AM
You should be able get 5v from the ISA Bus pin B3. See Here (http://pinouts.ru/Slots/ISA_pinout.shtml) Preferably, trace to a point on the card that can easily be soldered to and run a wire from there to the pin 7 on the connector as long as it is NC. If necessary, you can solder to the finger of the edge connector, but be careful not to let the solder get to far down on the finger so that it doesn't get into the ISA connector when the card is plugged in. You may need to cut a trace if pin 7 is connected. I don't have the schematic in front of me for the IBM CGA card but it should be easy enough to check visually or with a meter.

I believe this is what David_M indicated when he said "You will need to get a non switchable CGA video card that has no connection on pin 7 and connect it to a 5V source on the card." in post #2.

Wouldn't be easier to use any wall wart psu ? Get an old cellphone charger (the ones before the USB) that does 5V and voila or buy these universal psu at any electronics shop.

ibmapc
October 15th, 2017, 12:12 PM
Wouldn't be easier to use any wall wart psu ? Get an old cellphone charger (the ones before the USB) that does 5V and voila or buy these universal psu at any electronics shop.

Might be "easier", but not as tidy. He would have another cord to manage and use another outlet on his power strip. Plus, he would need to purchase the "wall wart". So, in My mind, not easier after all.

RobertK
October 17th, 2017, 04:59 AM
Hi soviet9922,
I would recommend to forget about the "pin 7" solution and use an external power supply. That of course means one more cable hanging from your adapter, but it has the advantage that your historic hardware will be kept unmodified. I simply connected a Micro-USB plug cable (so that I can plug in any cellphone charger), check your local electronic store for such a ready-made cable. I used item number 1414354 - 62 from Conrad which is currently sold out, but here (http://www.conrad.com/ce/en/product/1535015/?insert=62&insertNoDeeplink&productname=Connector-straight----------BKL-Electronic----Content-1-pcs) is another such cable.

soviet9922
October 19th, 2017, 11:21 AM
Thanks for the ideas, guys i thing im going to use the external psu option so i can change the adapter to other systems easy.

Retro Canada
October 19th, 2017, 12:07 PM
You will need to drive 12v to the pin 8 to activate the 4:3 aspect ratio as well 3V to pin 16 for the RGB blanking, otherwise it will take the composite input...

If you use the Scart 2 HMDI you can override the aspect ration on it using the OSD menu...

soviet9922
October 20th, 2017, 06:19 AM
You will need to drive 12v to the pin 8 to activate the 4:3 aspect ratio as well 3V to pin 16 for the RGB blanking, otherwise it will take the composite input...

If you use the Scart 2 HMDI you can override the aspect ration on it using the OSD menu...

Thanks for the info but in my case i have some monitors that i hacked rgb into them don't need power to switch to RGB.

FishFinger
October 21st, 2017, 01:37 AM
You will need to drive 12v to the pin 8 to activate the 4:3 aspect ratio as well 3V to pin 16 for the RGB blanking, otherwise it will take the composite input...


A lot of SCART devices didn't quite follow the spec properly, so most TVs have a way to force RGB mode.

soviet9922
February 21st, 2018, 05:18 PM
Got the adapter up an running at least the color part :D, now playing magy duck on a sony kx27ps1 that i got for 10 bucks only have to replace 3 caps and is running like new!.
The sync mixing part i build the schematic using the ic mixer and burned 2 times the ic then i realized that i have the + and - tips swapped on the multi-meter :mad:
Using 5+ for the rgb blanking signal to scart the speks says 3v not sure if this 2v over voltage could be bad for the monitor.

Now using the composite output from the CGA card as sync but when i get more SN74xx chips going to do it again :P.

https://preview.ibb.co/k3Vr0x/IMG_20180221_222241.jpg (https://ibb.co/cTF27c)
best free image host (https://imgbb.com/)

musicforlife
February 21st, 2018, 10:01 PM
Got the adapter up an running at least the color part :D, now playing magy duck on a sony kx27ps1 that i got for 10 bucks only have to replace 3 caps and is running like new!.
The sync mixing part i build the schematic using the ic mixer and burned 2 times the ic then i realized that i have the + and - tips swapped on the multi-meter :mad:
Using 5+ for the rgb blanking signal to scart the speks says 3v not sure if this 2v over voltage could be bad for the monitor.

Now using the composite output from the CGA card as sync but when i get more SN74xx chips going to do it again :P.

https://preview.ibb.co/k3Vr0x/IMG_20180221_222241.jpg (https://ibb.co/cTF27c)
best free image host (https://imgbb.com/)

Where you can find that game or did you mispell the name?

soviet9922
February 22nd, 2018, 04:59 AM
Where you can find that game or did you mispell the name?

is this game :
http://www.vcfed.org/forum/showthread.php?42849-MagiDuck-a-DOS-CGA-text-mode-game-project
And yes i mispell it.

soviet9922
April 18th, 2018, 11:58 AM
found another schematic for a vga - scart adapter.
This one don't need external power to mix the H-V to Composite Sync.
http://www.nexusuk.org/projects/vga2scart/circuit
What you guys think it could work ?
45093