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 »

Hi Stew and John
Thank you for your advices.
For the moment, I can't reduce the oscillation which causes the vertical lines by putting caps on the power supplies near the 6847 circuit. I will carry on my investigations.
My two Dragon RGB have the same behaviour.
In RGB output, the vertical lines are not so bad on all screens, variable with colors, and can be totally reduced on the green, by setting brightness, contrast and gamma when possible.
The RGB circuit is very simple, much more simple than the Dragon Plus card, John !
I will post the schematics of this RGB conversion, it is a four stages circuit using transistors.

The SECAM circuit is a nice relic. The Voltage Controlled Oscillator is also made with transistors on CA3046, there are several caps and selfs for tuning and filters. The quality is not so bad with my little amplifier (see photo).
Last edited by Azerpy on Sun May 09, 2021 6:25 pm, edited 1 time in total.
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 »

Dragon 32 SECAM OUTPUT.jpg
Dragon 32 SECAM OUTPUT.jpg (2.69 MiB) Viewed 2029 times
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 have looked on my Dragon 32 SECAM at the RGB conversion which is part of the PSU board.
On my schematics below, we can see that phi A (R-Y) and phi B (B-Y) signals of the 6847 are mixed to make the (G-Y) information.
The LUM, which is a clone of (- Y) information is inverted and then combined with (R-Y), (B-Y) and (G-Y) to get the three R G B colors. The Synch signal is the same as the Green.
D9 and R20/R21 give the bias of Q5.2 transistor and the voltage references. The offset of the outputs are different but that has no importance on the (modern ?) screens.
The tiny capacitor C11 is important for the contrast, I had to replace it by a 47 pF.
As I wrote before, all the machines that I know give too much blue, that can be corrected by the output resistors or by the settings of the screen.
Gérard
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 »

Here are the schematics.
Dragon 32 SECAM RGB part of PSU Board
Dragon 32 SECAM RGB part of PSU Board
circuit rvb.jpg (5.26 MiB) Viewed 1855 times
retrocant
Posts: 9
Joined: Sat Jul 24, 2021 2:02 pm

Re: Dragon 32 RGB SECAM and video tests

Post by retrocant »

Azerpy wrote: Sun May 09, 2021 6:17 pm Here are the schematics.
circuit rvb.jpg
Greetings, could you complete the value of the resistors that has to be put, I would like to carry out tests to be able to make a pcb.
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 »

Here are the missing values of components. Happy to help you in this project.
Attachments
missing values RGB.jpg
missing values RGB.jpg (742.26 KiB) Viewed 1120 times
retrocant
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Joined: Sat Jul 24, 2021 2:02 pm

Re: Dragon 32 RGB SECAM and video tests

Post by retrocant »

Thank you very much for publishing the missing information, I have already made the schematic and I intend to make a pcb and it will be signed by you as the author of the project. very grateful for your work.

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

Re: Dragon 32 RGB SECAM and video tests

Post by Azerpy »

Hello Alfredo
Incredible ! I am not yet able to create those beautiful schematics !
I have looked at yours, so I complete a little :
The good input of luma is not exactly the output Y of the VDG, it should be Y + the added lines that pads the signal for use the IC 6847 in Europe (625 lines). It must be taken after the multiplexor and the emitter follower transistor. For my Dragon, after IC11 and TR4, see above.
The U3 D transistor is not well connected, invert E and C.
It will be better with caps on +5 V and - 5 V (100nF and 1µF or higher on each).
The outputs are for Peritel, you need to put 1V to 3 V on the pin 16 to switch RGB. For exemple with 5 V + resistor of about 200 ohms
The basis of the transistors are not all connected to the ground on my pcb, don't know why, I think that is not important.
Have you a reason to put two VDG ?
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robcfg
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Location: Stockholm, Sweden

Re: Dragon 32 RGB SECAM and video tests

Post by robcfg »

The reason for the two VDG in the schematic is that one of them is actually the connector for the VDG socket on the motherboard and the second one is actually the VDG itself.
retrocant
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Joined: Sat Jul 24, 2021 2:02 pm

Re: Dragon 32 RGB SECAM and video tests

Post by retrocant »

Greetings, thanks for reporting the bugs I had, especially the U3D buff would have toasted ..

You are right in the part of the signal And that you have to take it after the multiplexer I have not realized it .. I rectify it ..

what the friend robcfg comments, I do not put two physical vdg chips, but what I do is to be able to puncture the socket from the vdg to the pcb followed by the vdg itself on my board, it is just an idea I also have to look if it has this one if has a socket or not (I don't remember)

I change the part of the Y signal and publish it.

I have also seen that D64 does not have -5V voltage I have to look to put a 7905 linear regulator or a voltage comparator to generate -5V

I also have to add the activation of the RGB in the peritel, the easiest thing is to enter the voltage + 5V and with resistance.

I need to know which diode is the one you put that I also lack.
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