Dragon 32 RGB SECAM and video tests

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Azerpy
Posts: 36
Joined: Tue Apr 09, 2019 1:16 pm
Location: France Pyrenées

Re: Dragon 32 RGB SECAM and video tests

Post by Azerpy »

So you have a Dragon 64. When I look at its schematics, I see a LM 7905 in the video section.
The diode is a clamp diode, any one is good for that like 1N914 or 1N4148. Mine is a little blue one.
https://en.wikipedia.org/wiki/Clamper_(electronics).

On my Dragon, this circuity is part of the power board, where, for your Dragon 64, it is empty near the DIN connector.
It seems possible to put a little PCB above this area.
I don't think it's a good idea to remove all the signals of the VDG ?
Attachments
RGB pcb.jpg
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retrocant
Posts: 9
Joined: Sat Jul 24, 2021 2:02 pm

Re: Dragon 32 RGB SECAM and video tests

Post by retrocant »

Thanks for the information about the diode, I was already thinking of putting a 1n4148 diode but you have confirmed it, I am not going to remove the vdg chip, since I have seen that it is already soldered on the board, I have an American tandy coco 2 and it has a socket and I had in Mind the one with the vdg chip socket.

I will change the strategy in the placement of the rgb pcb.

I keep you informed.
dublevay
Posts: 90
Joined: Wed Jan 23, 2019 3:41 pm

Re: Dragon 32 RGB SECAM and video tests

Post by dublevay »

Very interesting to see the schematic. It seems more simple than the board implies though. For instance, where are all of the RF tunable inductors and the delay device? Or is that just for SECAM RF?
dublevay
Posts: 90
Joined: Wed Jan 23, 2019 3:41 pm

Re: Dragon 32 RGB SECAM and video tests

Post by dublevay »

Very interesting to see the schematic. It seems more simple than the board implies though. For instance, where are all of the RF tunable inductors and the delay device? Or is that just for SECAM RF?
Azerpy
Posts: 36
Joined: Tue Apr 09, 2019 1:16 pm
Location: France Pyrenées

Re: Dragon 32 RGB SECAM and video tests

Post by Azerpy »

As I explained before, the SECAM circuitry with the tunable inductors and delay device is on the mother board. I have not yet published its detailed schematics. It would be only for fun ! Is there anybody interested by a french SECAM circuitry ?
On the power board, we have the RGB conversion with the transistors included in two IC1 and IC2 (CA3046) and the resistors, caps and diode around. Plus the four output transistors.
Near this, you can see another IC3 (CA3046) and a tunable inductor, that's a rather complex circuitry for sound to the RF modulator.
So the RGB pcb is very limited, with a very classical circuitry.
I have also got a Tandy coco 2b with a RGB output. The quality is better, it should be interesting to copy that circuitry too, but not as easy to do as for the Dragon one.
There are also some (only french ?) Dragons, related in forums, with a piggy RGB PCB.
dublevay
Posts: 90
Joined: Wed Jan 23, 2019 3:41 pm

Re: Dragon 32 RGB SECAM and video tests

Post by dublevay »

Hi - I just wanted to let you all know that I have asked Phill if I can run a batch of his excellent RGB boards - and he has agreed. It will be a while before I can do so - and I have no idea about pricing yet. I will put a seperate post in the Hardware forum.

I don't want to curtail any development of this RGB board, as the more development the better, but just thought I'd better openly declare my intentions.
Azerpy
Posts: 36
Joined: Tue Apr 09, 2019 1:16 pm
Location: France Pyrenées

Re: Dragon 32 RGB SECAM and video tests

Post by Azerpy »

I agree that "the more development the better" as you say John.
The RGB board seems interesting, but I understand that the MC 6847 has to be removed ...
Waiting for the schematics !
dublevay
Posts: 90
Joined: Wed Jan 23, 2019 3:41 pm

Re: Dragon 32 RGB SECAM and video tests

Post by dublevay »

Yes, the MC6847 has to be removed - but I have already sold numerous lower case boards, so many people have already undertaken this. As Pere said, the Coco VGA also requires the MC6847's removal.
retrocant
Posts: 9
Joined: Sat Jul 24, 2021 2:02 pm

Re: Dragon 32 RGB SECAM and video tests

Post by retrocant »

Greetings, I enclose the prototype pcb of how the idea of removing the RGB signal from Dragon32 / 64 would be, I have tried the following idea:

Integrate the board into the VDG, but as is being discussed you have to unsolder the VDG chip.

integrate the YUV signals by cable method without actually desoldering the VDG.

Integrate a 7905 linear regulator to get the necessary voltage -5V since the D64 does not have this voltage.


Voltage selection -5V either external or internal since the D32 does have -5V voltage.
Attachments
Captura de pantalla 2021-09-15 a las 11.12.46.png
Captura de pantalla 2021-09-15 a las 11.12.46.png (266.21 KiB) Viewed 589 times
Captura de pantalla 2021-09-15 a las 11.12.31.png
Captura de pantalla 2021-09-15 a las 11.12.31.png (294.08 KiB) Viewed 589 times
bluearcus
Posts: 97
Joined: Wed Sep 07, 2016 4:45 pm

Re: Dragon 32 RGB SECAM and video tests

Post by bluearcus »

Hi retrocant and everyone else here...

Interesting board idea and documentation of the original SECAM RGB stuff. I've a question though... How does the original SECAM board circuit get its luminance signal? It can't be direct from the 6847 as there wouldn't be properly formed 'extra PAL' lines?

A board using this approach would surely need to steal the luminance after the extra lines mixing, not direct from the 6847?

Maybe you're already coping with that though and I've misunderstood?

Kind regards,

Mike
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