Naive question about SCART connection on TV

[martyn_hill]

Hi ProF

Not quite - the QL definitely provides TTL-level output on the RGB (and V / C-Sync) lines.

My preferred reference on building a suitable SCART lead for the QL is here: http://www.fruitcake.plus.com/Sinclair/ ... ableQL.htm

[Pr0f]

I believe the RGB outputs are 1V video on the 8 pin connector - as there are resistors on the motherboard between the socket and the video ULA.

Actually not - seems the resistors are for the RGB encoder chip for composite / UHF signal output - the circuit board shows these are coming straight from the ULA - so assuming 5V ttl signals

[Pr0f]

Hi ProF

Not quite - the QL definitely provides TTL-level output on the RGB (and V / C-Sync) lines.

My preferred reference on building a suitable SCART lead for the QL is here: http://www.fruitcake.plus.com/Sinclair/ ... ableQL.htm

I should go look a the circuit diagram first

[martyn_hill]

RTFM has always been my greatest failing, too

[georgeo]

Hi everyone,

Thanks for your various replies. This is more complicated than I imagine.

I should also correct something I said earlier. My TV does not allow me to manually select between SCART (composite) and SCART RGB. It simply has a SCART source, so I assume it relies on getting the right signals to set the mode.

I do have a SCART cable for my Spectrum +3, though this doesn't work. in fact, that cable doesn't even work on our main TV, which has two SCARTS with one labelled explicitly as RGB. It produces a white screen with a very faint grey shadow of the text that should be displayed. However, I've read in various places that there is a problem with the RGB output on many +3's, which means it doesn't work properly.

I suspect my best bet will be to buy a cable and see if it works.

I'll report back with the result in due course!
George.

[Zarchos]

Hi ProF

Not quite - the QL definitely provides TTL-level output on the RGB (and V / C-Sync) lines.

My preferred reference on building a suitable SCART lead for the QL is here: http://www.fruitcake.plus.com/Sinclair/ ... ableQL.htm

What voltage is sent between pins 16 and 18 of the SCART connector ?
Standard definiton says 3V is max.

[Dave]

Source: QL Service Manual

[tofro]

Hi ProF

Not quite - the QL definitely provides TTL-level output on the RGB (and V / C-Sync) lines.

My preferred reference on building a suitable SCART lead for the QL is here: http://www.fruitcake.plus.com/Sinclair/ ... ableQL.htm

What voltage is sent between pins 16 and 18 of the SCART connector ?
Standard definiton says 3V is max.

My layman's interpretation:

The LM317 is specified to deliver the voltage at ADJ + 1.25V.

With the diode in the path, you can assume ~0.7V at ADJ, which ends up as an output Voltage of 1.95V

[1024MAK]

Hi everyone,

Thanks for your various replies. This is more complicated than I imagine.

I should also correct something I said earlier. My TV does not allow me to manually select between SCART (composite) and SCART RGB. It simply has a SCART source, so I assume it relies on getting the right signals to set the mode.

I do have a SCART cable for my Spectrum +3, though this doesn't work. in fact, that cable doesn't even work on our main TV, which has two SCARTS with one labelled explicitly as RGB. It produces a white screen with a very faint grey shadow of the text that should be displayed. However, I've read in various places that there is a problem with the RGB output on many +3's, which means it doesn't work properly.

I suspect my best bet will be to buy a cable and see if it works.

I'll report back with the result in due course!
George.

It sounds like your TV's will need a source of 1V to 3V on pin 16 of the SCART connector to tell the TV to use the RGB input pins. This goes for the +3 as well.

You can either use the LM317 circuit shown in the link to Paul's Fruitcake site (in one of the above posts), or use a suitable resistor. Either way, you need a external supply.

Can you solder?

Mark

[georgeo]

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Tonight, I am a very happy QL owner. New RGB to SCART cable from Retro Computing Shack is working beautifully. Thanks to everyone for your help, George.