Woes of Amiga RGB to SCART

[TheCorfiot]

@thread

I had a look inside my RGB cable on the weekend which I built in 1987

I am feeding the Amiga's compsync signal (pin 10) to the scarts video in (pin 20) & then using a reverse biased diode linking pin 20 & 16 on the scart, ie just passing the -ve going sync pulses from compsync signal to the Fast blanking TV input, It has worked flawlessly and with many different types of TV too.
There is no other connection being made to pin 16 on the scart apart from the reversed diode feed.

Don't ask why I did it this way as it was really too long ago. maybe something to do with my A1000 being difficult to hook up at the time if I remember, then when my A500 / A1200 / A2000 came along the cable still worked fine.

TC

[Merlin]

@ Zetr0

Don't despair mate, every cloud has a silver lining.....

[Zetr0]

Originally Posted by TheCorfiot

@thread

I had a look inside my RGB cable on the weekend which I built in 1987

I am feeding the Amiga's compsync signal (pin 10) to the scarts video in (pin 20) & then using a reverse biased diode linking pin 20 & 16 on the scart, ie just passing the -ve going sync pulses from compsync signal to the Fast blanking TV input, It has worked flawlessly and with many different types of TV too.
There is no other connection being made to pin 16 on the scart apart from the reversed diode feed.

Don't ask why I did it this way as it was really too long ago. maybe something to do with my A1000 being difficult to hook up at the time if I remember, then when my A500 / A1200 / A2000 came along the cable still worked fine.

TC

any chance of a drawing m8y? I sense a SCART method 8 has been found.

[TheCorfiot]

Hiya Z

I coud modify an existing drawing, It was a very simple mod...

All RGB lines wired in....
CSync to Pin 20 on the scart & asociated GND...
1n4148 diode cathode connecting to pin 20 on scart (CSYNC)
Anode of said diode connecting to pin 16 on scart (FB), no other connection to pin 16.

If my memory serves (god it's blurry) I had to use this kind of arrangement because my A1000 would not play ball...
The CSYNC from the A1000 was also not quite right and I had to wire in a flying RCA lead to take the Monochrome video out & use that in parallel with the CSYNC generated by the 23 pin Video port...

When the A500 came along the flying RCA lead became redundant as too with the A2000 / A600 & A1200..... IT worked perfectly with all these models...

The A4000 that I picked up earlier this year however did not like this cable (CSYNC again !!!) & due to no monochrome output availability I modded the lead to provide a fixed voltage on the FB pin instead....

We can talk about it when we catch up if you like...

Best Wishes
TC

Hi guys!

I've just spent an afternoon fighting to get RGB video from my Amiga 500 to a Samsung LCD TV via SCART. I frantically searched the web for information and stumbled upon this thread - very useful information here! Anyway, I had to register to post my not-so-elegant but working solution - hopefully it'll be of use for someone.

Problem #1 was the blanking signal. I tried a number of different sizes of resistors from my bit box but none seemed to work and I couldn't find a trimmer of suitable size, either. I did have some LEDs though, and given that the voltage drop of a normal red LED is about 1.7V, this would drop the 5V output from Amiga to a nice 3.3V. I connected the anode to the 5V output from Amiga and wired the cathode to pin 16 on the SCART. And what do know - it worked!

Well, for a while - occasionally the image would go all berzerk as if the sync had completely gone. Aaand that's problem #2 right there.

I found out that the Amiga feeds TTL level CSYNC signal to the modulator and most TVs would expect the CSYNC in SCART to be of normal composite video levels 0V to 1V. A few LEDs might do the trick here, too - but I didn't want any more lights blazing behind my TV so I used five normal 1N4148 diodes in series to drop the voltage (each has a forward drop of about 0.7V) to about 1.5V and the TV seemed happy with this.

This solution meets all the characteristics of a hack but it did seem to work for me. Although had I not been too lazy, I might've popped down to the local electronics store to pick up some zener diodes to cleanly clamp the voltages down but, well.. I'm lazy.

[alexh]

Originally Posted by Zetr0

I sense a SCART method 8 has been found.

It wont help.

Because the name of the input is sometimes called "Fast Blanking" at some time in the past someone thought they needed to wire it to the video blanking output (i.e. H/VSync). It works if you do, but not by design. This error has been replicated everywhere, not just on the Amiga. It is almost a common a mistake in Amiga SCART cables as having resistors on the RGB wires!!

This signal was originally designed to be a sort of genlock signal allowing RGB video overlay on top of live TV anywhere on the screen. You could turn it on/off anywhere. However everything today (DVD's, set-top-boxes, consoles etc) drive it to RGB levels constantly. This will _not_ be the source of your problems.

I created a table a while ago which provides the most comprehensive information for wiring.

http://eab.abime.net/showpost.php?p=572128&postcount=18

Originally Posted by firehawk

I found out that the Amiga feeds TTL level CSYNC signal to the modulator and most TVs would expect the CSYNC in SCART to be of normal composite video levels 0V to 1V.

True that it is TTL. However most TV's just don't care. It is only the new LCD & Plasma tv's which have a video processor in that care.