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Author Topic: C52 with PAL video mod.  (Read 17437 times)
gertk
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« Reply #15 on: February 25, 2012, 09:43:06 PM »

Did you connect pin 8 of the SCART to anything ? (the AV switch input)

The scart input will do fast blanking (RGB status) but no synchronisation to pin 20 if you do not send at least 6 Volts into pin 8. (on widescreen TV sets 6 Volts will signal a 16:9 format and 12 Volts a 4:3 format) With fast blanking only you will see a rolling screen.

When switching to the scart input manually on the TV set it should always sync to pin 20.
 
« Last Edit: February 26, 2012, 01:44:09 PM by gertk » Logged

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Tibopac
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« Reply #16 on: February 29, 2012, 02:11:58 PM »

No, I didn't connect pin 8 of the SCART to anything, and before switching on the console, I always switch my CRT TV to the AV channel manually.
So if I have understood correctly, the problem comes from elsewhere.
Actually, I'm not 100% sure of picking the sync signal at the right place as I'm not totally sure of knowing which components on the C52 play the role of the IC656 or IC663 on the G7200 diagram.
I'll do more tests next week and take pictures. I'll keep you advised.
Thank you all for your help.
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gertk
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« Reply #17 on: February 29, 2012, 07:02:45 PM »

Simple trick to check if your scart input is working OK:

Connect the TV to an aerial or cable outlet and make sure it has a picture.
Switch to AV/SCART on the TV set (picture will blank)
Connect pins 19 and 20 (temporarily) together and if the scart input is OK you will see your TV channel again (loop between video out and input). If that works it should sync also to external signals (if they are the right voltage/polarity/frequency and such)

In your C52 is the modulator part still working ? If so you must be able to find the composite video and sync signal somewhere on the modulator board and maybe use that for a sync signal to the SCART input.
I do not have a circuit diagram for the C52 so unfortunately can not check what goes where  Smiley
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Tibopac
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« Reply #18 on: March 10, 2012, 05:48:01 PM »

Hi,

I'm not sure to understand what that trick is supposed to check. If it's the scart input on the TV, I'm sure it works well as every other console I plug to it (either RGB or Composite) works perfectly. If it's the RGB mod that it is supposed to check, then ok, I should try.

Anyway, I tried that trick.

I first connected an Atari 2600 to the aerial socket of my TV and got a picture. Then I switched on the C52 connected to the AV input and the C52 image appeared and rolled diagonally (so without swiching to AV input manually).

Then I switched off the C52, checked again that I still had the aerial picture, switched manually to AV input (black screen), and switched on the C52. The picture rolled fast horizontally and slowly vertically. Then I connected pin 19 to pin 20 on the C52 RGB board without switching off the C52, the picture roll changed to a diagonal roll (the same way it rolled when I did not switch to AV manually).

So I guess the result is a bit different from what was expected. Connecting pin 19 to 20 did switch from AV input to Aerial input but I didn't get the Atari picture, and there was no loop, just one switch.


I removed the modulator part but maybe, as Rene said, I can find that sync signal on one of the links between the main board and the modulator. I think I found somewhere that it was link 14 but I'll check that again.

I think I'll do the transistor part of the mod again, maybe there is something wrong with it...

Thanks and see you soon.
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gertk
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« Reply #19 on: March 10, 2012, 10:40:15 PM »

I'm not sure to understand what that trick is supposed to check. If it's the scart input on the TV, I'm sure it works well as every other console I plug to it (either RGB or Composite) works perfectly. If it's the RGB mod that it is supposed to check, then ok, I should try.

That was what the test was for indeed, just to check if the scart composite input (or sync in case of RGB input) was working. Since you state that it works with other devices I assume the scart input is OK.

Quote
So I guess the result is a bit different from what was expected. Connecting pin 19 to 20 did switch from AV input to Aerial input but I didn't get the Atari picture, and there was no loop, just one switch.
You did not get the Atari picture because the C52 still provided the fast blanking signal which overrides the composite signal.

Quote
I removed the modulator part but maybe, as Rene said, I can find that sync signal on one of the links between the main board and the modulator. I think I found somewhere that it was link 14 but I'll check that again.

I do not have the C52 circuit diagram so I can just speculate: The 8245 itself does not generate composite sync signals, they are created in the G7000/7200/7400 with a bunch of logic gates and counters (and even a special PROM). It is also dependant on the color system. PAL/SECAM and NTSC all have different logic to generate the proper sync signals.
There is a fair chance that part of the sync signal is generated on the removed modulator board.

Without an oscilloscope or a detailed circuit diagram to find the right signal it is going to be tricky.
« Last Edit: March 11, 2012, 03:23:26 PM by gertk » Logged

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Rene_G7400
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« Reply #20 on: March 11, 2012, 01:17:17 AM »

I've just tried to pick the sync signal from pin 11 of the only 74LS00 I found on the board (IC663, I think you meant this one).

On an older version of the C52 I see that they have given this 74LS00 the number 7670.
If there is something wrong with the blanking signal, your TV will also get sync problems.
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Tibopac
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« Reply #21 on: March 30, 2012, 07:07:03 PM »

Thank you Gertk & Rene ! Sorry for answering so late, I don't have much time those days. I think I will be able to take care of my videopac and check what you both mentioned by the end of april. I'll keep you advised then. Thanks again for your help !
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Speedy1102
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« Reply #22 on: July 06, 2012, 06:34:28 AM »

I also got an Radiola Jet 25 here with this Board.

Anyone managed to mod this Board for AV of RGB out ?


Thanks.

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Tibopac
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« Reply #23 on: July 06, 2012, 12:37:17 PM »

I still haven't tried the latest advice (even if April is over now Wink ). But I will, this summer I hope. So for me, I still have a picture but no sync.
If you manage to have a steady picture, keep us advised Wink
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gertk
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« Reply #24 on: July 06, 2012, 07:50:01 PM »

A circuit diagram of the Jet 25 would be nice..  Wink
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Speedy1102
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« Reply #25 on: July 08, 2012, 08:27:25 PM »

How many Signals are required for RGB out ? Red, Green, Blue, Sync Huh?? and how to probe them with an Oscilloscope ?

Whats the Difference between  the Pal and The SECAM output of the Consoles.

Thanks

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gertk
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« Reply #26 on: July 09, 2012, 07:46:29 AM »

How many Signals are required for RGB out ? Red, Green, Blue, Sync Huh?? and how to probe them with an Oscilloscope ?

For scart RGB you need Red (pin 15), Green (pin 13), Blue (pin 11), Composite Sync/video (pin 20), a fixed voltage for Fast Blanking (pin 16) and a fixed voltage for switching the TV to AV mode (pin Cool and ground (pin 17)

For the composite sync signal (pin 20) you can use the composite video signal which goes into the modulator of the JET 25 but it might need to be buffered (with an emitter follower) The R/G and B signals can be made the same way as they are made in the G7401 or G7200 with a 7407 chip and a bunch of resistors and diodes.

Quote
Whats the Difference between  the Pal and The SECAM output of the Consoles.
Different countries use different standards for TV sets, difference between PAL and SECAM is the color coding system. For RGB this makes no difference as the colors are not encoded. You just need a suitable sync signal.

This is how it is done in the G7200, the part numbers will be different!
« Last Edit: July 16, 2012, 07:20:00 AM by gertk » Logged

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Speedy1102
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« Reply #27 on: July 10, 2012, 12:47:34 PM »

The linked Plan looks good. But the Part numbers are totally different on this Board. Only Numbers.

Do you have Plans for the Radiola Jet 25 also ?

I Thinks i will buy a G7000 Unit. Much easier to mod for composite.

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Rene_G7400
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« Reply #28 on: July 10, 2012, 06:12:13 PM »

If you want RGB, buy a G7400, even easier to mod.
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VideopacBelgium
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« Reply #29 on: July 10, 2012, 09:16:54 PM »

This is my mod
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