Composite to Scart - What am i doing wrong

[Adrian45]

Hello again good people.

Trying to hook my 48k issue 4 to my color monitor

Color monitor has a scart input , some kind of 5 pin din input for r,g,b, and a single phono input for audio.

I have read that pin 20 and pin 17 on the scart connector are the composite input and composite in ground.

So as a quick test i soldered 2 wires from the end of my composite lead to pins 20 and 17

but nothing

reversed them , nothing

I know little about composite signals , even less about scart cables

am i doing something wrong here

[Adrian45]

strangely , if i leave the ground in 17 and take the comp signal from pin 20 and put it in either the red , green or blue i see the spectrum screen , in red , green or blue ........

so there is a signal there but no composite display from pin 20

the composite mod i did on the spectrum was using the 100 uf capacitor , cutting the 5 volt feed into the modulator and disconnecting the resistor to the signal out

In the recap kit I got there was another composite mod with transistors for some monitors that were 'different' ...... wonder if this is one of them ?

any ideas ?

[rich_r]

Not all devices have to honour all the different video signals possible on SCART, just the ones they support. So it's likely that the monitor only accepts RGB components and not composite - so there will be nothing connected in the socket for the composite pin inside the monitor.

I'm using a 15" Philips TV that I bought in 1988, which does support composite on SCART, for my Spectrum. It's served me well on Spectrum, Atari ST, Amiga and also as a TV I believe Philips also sold the same basic unit as a monitor, just without the tuner and teletext boards and remote control.

[1024MAK]

Although most TVs support composite video inputs on their SCART sockets, not all monitors do. So the first thing is to check any documentation for your monitor.

The fact that you can get an monochrome red, green or blue image if you use one the red, green or blue RGB inputs without having to provide the correct switching input voltage on pins 8 and 16 or manually switching to RGB mode also indicates that your monitor may not support composite video inputs.

To support a colour composite video, the monitor would need to include a colour decoder circuit. Monitors designed for use with computers that have RGB outputs, typically did not include this circuitry, to keep costs lower.

For the record, the composite video input signal should be connected to SCART pin 20. The 0V/ground pin is 17. If using a co-ax cable or a cable with a single signal wire and a screen, the screen is connected to pin 17.

It is possible to use the red, green or blue inputs to give you a white grey scale image, but you would not have a full colour image.

Mark

[Adrian45]

Hello again Mark, and again thank you for sharing your knowledge.

thats was the kind of answer I was hoping NOT to get !!!! - cause it makes sense and seem right - The monitor looks like it does not
take a composite signal. Especially with the other 5 pin din connection saying RGB input.

Just flipped over the monitor to have a look at the back - to my surprise it is a monitor that was built for Acorn - Cant see a brand name just a letter 'M'
on the front of it. Pity , its a great color monitor. I have used it for an Oric atmos , electron , cbm64 all with leads I made myself.

Easy answer - Ill get a different monitor.

Have to see this spectrum in its full color glory

Thanks again people.

[jamesh]

User guide says it's RGB only.

[Gooeyblob]

You might be able to fit a composite connector to that monitor, it has markings for cvbs input, on a lot of those rebadged Philips (cm8833) monitors you can.

[oO cozy Oo]

Does scart need voltage for it to switch?
"Notice the +5 volts applied to pins 8 and 16. These are signal pins, pin 8 tells the TV which aspect ratio to select and pin 16 tells the TV to select RGB mode. Pin 16 must have at least 1.3 volts applied to it or the TV will ignore the RGB signal and fall back to composite"

or

"Blanking and switching
Two pins provide switching signals.

Pin 8, the switch signal pin, carries a DC voltage from the source that indicates the type of video present.

0 V–2 V means no signal, or internal bypass
4.5 V–7 V (nominal 6 V) means a widescreen (16:9) signal
9.5 V–12 V (nominal 12 V) means a normal (4:3) signal
Pin 16, the blanking signal pin, carries a signal from the source that indicates that the signal is either RGB or composite.

0 V–0.4 V means composite.
1 V–3 V (nominal 1 V) means RGB only.
The original specification defined pin 16 as a high frequency (up to 3 MHz) signal that blanked the composite video. The RGB inputs were always active and the signal 'punches holes' in the composite video. This could be used to overlay subtitles from an external Teletext decoder.

0 V–0.4 V means composite with a transparent RGB overlay.
1 V–3 V (nominal 1 V) RGB only.
There is no switching signal to indicate S-Video. Some TVs can auto-detect the presence of the S-Video signal but more commonly the S-Video input needs to be manually selected. The same for the rare component YPbPr, which is in many cases implemented over a composite or RGB SCART."

[1024MAK]

You might be able to fit a composite connector to that monitor, it has markings for cvbs input, on a lot of those rebadged Philips (cm8833) monitors you can.

Will not help if it lacks the PAL colour decoder circuitry...

Does scart need voltage for it to switch?
"Notice the +5 volts applied to pins 8 and 16. These are signal pins, pin 8 tells the TV which aspect ratio to select and pin 16 tells the TV to select RGB mode. Pin 16 must have at least 1.3 volts applied to it or the TV will ignore the RGB signal and fall back to composite"

You normally need to apply the correct voltages to switch from the default "composite video" mode to RGB mode. Not the other way round...

If the monitor does not have a composite video input, then the default is RGB mode as there is no other available mode.

Mark