RGB cable... strange fault ..

Started by retro_4_ever, 13:58, 28 April 21

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retro_4_ever

interesting RGB fault .. i have done a few cables that work fine on a few different 464's using my main tv .. so i have another tv (early bush 4:3 flat screen) and when i connect a 464 to it the RGB signal is displayed in black & white (only when using the lum as sync) .so this suggests that the RGB is not switching  but when switching tv to YCrCb it shows a great picture but with wrong colours. when in a RGB zx spectrum is connected it works fine .. so this has been bugging me so i looked at the RGB signals and the red line is showing over 2 volts but this is coming from the tv not the cpc .. so i checked the resistance to the TV RGB lines with power & cpc disconnected, green & blue where about 76 ohms and red was 70 ohm .. so. is the TV FUBAR ? could the slightly low resistance be causing this problem >?

Bryce

Can the TV be manually set to RGB on SCART?

Bryce.

retro_4_ever

yeh, you can manually select all the different scart signals - you have to as it does not auto detect..

Bryce

So you've manually selected RGB on SCART yet it gives you a black and white picture?

Bryce.

retro_4_ever

yeh.. this is when using lum to pin 20 of scart  and sync output as blanking.. if i use sync on pin 20 and external voltage for blanking then it shows nothing on RGB unless you turn the brightness / contrast all the way up.. strange that i get a picture on YCrCb i thought  this is component and a different signal requirement  + surprised it is there at all, as the tv only has scart input

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