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VA0 JAP Dreamcast and RGB

Started by djlooka, October 01, 2014, 12:10:39 am

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djlooka

Hi all, I have a Japanese VA0 Dreamcast, with a SCART "DC super RGB cable" by Diamond

the above picture is not mine, but the cable is identical.

When I connect it to my room's TV (on the RGB port - SCART #1) it only displays a B/W picture. The TV is a Mivar 21 MF51 stereo.

The weird things are:
- the same TV seems to support RGB correctly (my PAL PlayStation connected with an RGB cable does show a coloured image, even when playing NTSC/US or NTSC/J games);
- the 240p test suite (http://junkerhq.net/xrgb/index.php/240p_test_suite), when run on the Dreamcast, indicates "Composite" on the lower right corner (even if the cable should be RGB);
BUT
- the same Dreamcast and cable display correctly a coloured image on another TV (Philips CRT)!

My suspect is the TV, which may actually not support the NTSC format (and maybe the PlayStation somehow outputs the image in PAL60).

Any ideas?

eidis

 Hi Djlooka !

The TV senses input on SCART pin 16 which tells it to use either composite or RGB mode. More info in the following article:

SCART (Peritel; Euroconnector) connector pinout
http://pinouts.ru/Home/Scart_pinout.shtml

Keep the scene alive !
Eidis
X68000 personal computer is called, "X68K" or "no good good" is called, is the PC that are loved by many people today.

djlooka

Hmm, first of all thank you for your response.
Could you please elaborate more?

From what I read on that page, if the TV receives 1-3V on the 16th pin, switches to RGB, otherwise if it receives 0-0.4 V, it switches to Composite.
That might mean that my cable is faulty and fails to send the 1-3V to that pin (that would explain it).
Anyway it wouldn't explain why possibly the exact same console and cable displayed a correct coloured image on another PAL tv, wouldn't it?

eidis

October 02, 2014, 01:52:17 am #3 Last Edit: October 02, 2014, 02:04:57 am by eidis
 Hi Djlooka !

I think I might have a clue why your Dreamcast with the given cable is working in Composite mode. Please open the RGB decoder box and have a look inside. It could be that it transcodes the RGB signal into composite. If that is the case, you can still modify it and make it a true RGB cable. I use the following pins and trick to force RGB when making my custom cables.

7 - Blue
11 - Green
15 - Red
16 connected with 20 - Synchronization + force RGB (pin 16)
17 connected with 18 - Ground

The following pinouts were tested with Amiga, ZX-Spectrum, Amstrad CPC, Atari ST

P.S. Be carefull and connect or disconnect cables only when the Dreamcast is switched off. It has a very fragile video DAC which can be easily damaged.

Keep the scene alive !
Eidis
X68000 personal computer is called, "X68K" or "no good good" is called, is the PC that are loved by many people today.

djlooka

Thank you Eidis,
I am going to need to find my multimeter for further testing, anyway I opened the decoder box and upon a visual inspection everything looks fine.



Anyway I managed to test the console on a friend's TV (a Sony Trinitron CRT) and the image was coloured... I am puzzled.

eidis

 Hi Djlooka !

What is the part number of that SONY chip ? In the meantime, check out the attached schematic.

Keep the scene alive !
Eidis
X68000 personal computer is called, "X68K" or "no good good" is called, is the PC that are loved by many people today.

djlooka

October 02, 2014, 04:09:10 am #6 Last Edit: October 02, 2014, 04:14:19 am by djlooka
The Sony chip is marked as CXA1621S.
http://elm-chan.org/works/sc/report.html reports it as a "video decoder".
http://local16.com/knowledge/Video_Conversion.html confirms it is related to some NTSC/PAL conversion.

eidis

Hi Djlooka !

According to datasheet it is analog RGB to composite PAL/NTSC converter. You could omit it entirely and connect the wires according to the previously posted schematic if you are absolutely sure that your TV can handle RGB through SCART.

Keep the scene alive !
Eidis
X68000 personal computer is called, "X68K" or "no good good" is called, is the PC that are loved by many people today.

djlooka

Ok so the cable needs to be modded :)
Since I'd like to retain its original functionality, I thought maybe I can just remove the board with the IC (store it for future reuse) and run some male-male jumper wires to the two white connectors.
I mean, connecting the wires coming from the DC plug to the ones going into the SCART plug, it should work, shouldn't it?

eidis

October 04, 2014, 05:42:41 pm #9 Last Edit: October 04, 2014, 06:32:13 pm by eidis
 Hi Djlooka !

Yes, but don't forget to add the 220uf capacitors and 560ohm resistor. You can purchase some pin headers which will make the task more easy.

10PCS 40Pin 2.54mm Single Row Straight Male Pin Header Strip PBC Ardunio
http://www.ebay.com/itm/10PCS-40Pin-2-54mm-Single-Row-Straight-Male-Pin-Header-Strip-PBC-Ardunio-/180974247480?pt=LH_DefaultDomain_0&hash=item2a22e7de38

Update: This might be an even better solution:

10x CH3.96mm pitch spacing 8 Pin Header Plug Terminal Connector Jack PCB Header
http://www.ebay.com/itm/10x-CH3-96mm-pitch-spacing-8-Pin-Header-Plug-Terminal-Connector-Jack-PCB-Header-/111472962988?pt=US_Power_Cables_Connectors&hash=item19f44e6dac

Keep the scene alive !
Eidis
X68000 personal computer is called, "X68K" or "no good good" is called, is the PC that are loved by many people today.