SCART lead shenanigans

[Merlin]

I acquired a SCART lead from a member on here a while back that was described as 'not working'. Tonight I thought that I'd take a look at it and hooked it up to an A500+ and tried it on a portable TV.

I got a blank screen, but if I briefly changed the channel and switched back to SCART I got a brief flicker of a colour boot screen.

The cable is wired for both RGB and Composite as per this diagram.



Pin 17 (Video Ground) is connected to Pin 18 (RGB Blanking Ground) via a short jumper wire and there are no capacitors or resistors at all in this cable. Pin 8 (Switch +12v) is not wired up on this cable.

So, this is one for the SCART gurus out there. Is there anything unusual about how this cable is wired up and more importantly, is there anything missing that should be there? I am wondering if the RGB lines should have pull-up resistors on them.

I think that the brief flash of colour screen I see is possibly the Composite signal but it may be being over-ridden by the RGB lines.

I also know that SCART leads and Amigas can be a family sized can of worms, but I am open to suggestions about this one.

 

[TheCorfiot]

What's connected to pin 16 Dave

 

[Merlin]

Pin 16 isn't connected, Bas. Might this be the source of the problem?

 

[Chinners]

It is possible that the tv is going to rgb then quickly to composite (or the other way round). Can you manually select rgb or composite on your telly

ALso, in all the scart leads I have messed with, rgb blanking ground has always been left disconnected.

The basic schematic I have used is from the amstrad version...

http://www.cpcwiki.eu/index.php/TV_SCART_cable

I have found resistors and caps on rgb lines just tidy the image up, especially on crt displays.

(Oops. I missed the word ground from rgb blanking... kinda important!)

 

[Merlin]

@ Chinners

The portable here doesn't have that capability, but I have a multi-standard monitor that I'll try it with tomorrow, as I think that can select the input type.

It must be a good monitor, as WoodyCool was trying to scrounge it off me at Replay last year!

 

[TheCorfiot]

The cable you have there Dave is for connecting an Amiga to a 1084 scart..

You need to apply a voltage >3V to pin 16 to switch RGB mode on the TV set.
Use a spare core and hook up the +5v on the Amiga's 23 pin port to pin 16 of the scart via a 270ohm resistor......

That should sort you out..
TC

 

[Merlin]

Thanks, Bas

The cable on it at the moment has no spare cores, so I'll source some new multi-core cable and re-wire it. The cable could do with being a bit longer anyway, so that's OK.

 

[protek]

I got tired of trying to supply the pin 16 with voltage within the 1-3 volt treshold and got a TV that you can manually set on taking RGB from scart. If you don't have any use for the composite, open up your TV and try to supply the needed voltage to the pin 16 from within the telly. That way it's always forced to take RGB. Or maybe a little switch on the back so you can select whether to take composite or RGB.

 

[TomCrazy]

Thanks, Bas

The cable on it at the moment has no spare cores, so I'll source some new multi-core cable and re-wire it. The cable could do with being a bit longer anyway, so that's OK.

Is the +12V switching voltage wire hooked up to the SCART connector? You don't need the 12V switching signal. It's just a steady voltage that makes the TV automatically select the SCART input when the Amiga is turned on, if the SCART input is not already selected. But you don't actually need this, since you can select the SCART input with your remote control for the TV.
So if this wire is connected, you can desolder it an rewire it both on the Amiga side and SCART side to instead act as an RGB switching voltage.