Naive question about SCART connection on TV

Nagging hardware related question? Post here!
martyn_hill
Aurora
Posts: 909
Joined: Sat Oct 25, 2014 9:53 am

Re: Naive question about SCART connection on TV

Post by 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


User avatar
Pr0f
QL Wafer Drive
Posts: 1298
Joined: Thu Oct 12, 2017 9:54 am

Re: Naive question about SCART connection on TV

Post by Pr0f »

Pr0f wrote: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


User avatar
Pr0f
QL Wafer Drive
Posts: 1298
Joined: Thu Oct 12, 2017 9:54 am

Re: Naive question about SCART connection on TV

Post by Pr0f »

martyn_hill wrote: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
Aurora
Posts: 909
Joined: Sat Oct 25, 2014 9:53 am

Re: Naive question about SCART connection on TV

Post by martyn_hill »

RTFM has always been my greatest failing, too :-)


georgeo
Bent Pin Expansion Port
Posts: 95
Joined: Wed Aug 03, 2016 8:49 am

Re: Naive question about SCART connection on TV

Post by 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.


User avatar
Zarchos
Trump Card
Posts: 152
Joined: Mon May 08, 2017 11:49 am

Re: Naive question about SCART connection on TV

Post by Zarchos »

martyn_hill wrote: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.


Owner of various QLs including accelerated beasts, and also a happy Q68 owner ;)
Now porting SOTB to the Archies, to then port it to the Q68.
https://www.youtube.com/user/Archimedes ... +%28100%25
User avatar
Dave
SandySuperQDave
Posts: 2765
Joined: Sat Jan 22, 2011 6:52 am
Location: Austin, TX
Contact:

Re: Naive question about SCART connection on TV

Post by Dave »

Source: QL Service Manual
Source: QL Service Manual


User avatar
tofro
Font of All Knowledge
Posts: 2685
Joined: Sun Feb 13, 2011 10:53 pm
Location: SW Germany

Re: Naive question about SCART connection on TV

Post by tofro »

Zarchos wrote:
martyn_hill wrote: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


ʎɐqǝ ɯoɹɟ ǝq oʇ ƃuᴉoƃ ʇou sᴉ pɹɐoqʎǝʞ ʇxǝu ʎɯ 'ɹɐǝp ɥO
User avatar
1024MAK
Super Gold Card
Posts: 592
Joined: Sun Dec 11, 2011 1:16 am
Location: Looking forward to summer in Somerset, UK...

Re: Naive question about SCART connection on TV

Post by 1024MAK »

georgeo wrote: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


:!: Standby alert :!:
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer in Somerset later in the year :)

QL, Falcon, Atari 520STFM, Atari 1040STE, more PC's than I care to count and an assortment of 8 bit micros (Sinclair and Acorn)(nearly forgot the Psion's)
georgeo
Bent Pin Expansion Port
Posts: 95
Joined: Wed Aug 03, 2016 8:49 am

Re: Naive question about SCART connection on TV

Post by georgeo »

[img]
WP_20180205_001.jpg
[/img]

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.


Post Reply