External or SCART blanking
What blanking should I use?
I get asked this question a lot. I think it is time to put this in writing somewhere, so that this question can be answered for good 😃
What is blanking?
This is also known as fast blanking or YS. In layman terms, this is a digital switch to tell the chroma chip to display the R, G, B signal that is fed into it.
Slightly technical explanation.
Sending a 5V signal through the YS pin to the chroma (jungle) chip, blanks the other inputs and displays the external R, G, B signal that is fed into the chroma chip.
This method is then harnessed to do the R, G, B mux mod.
But, why a mux mod?
Do you want to see the OSD (on screen display) along with your RGB signal? Meaning, do you want to see the Menu options, Volume bars etc. layered on top of your RGB image? If you do, then you need to mux mod it. Therefore, you mux the blanking voltage along with the OSD. So, either one or both of those are able to ask the chroma chip to blank and display what is fed to it.
When is mux mod not needed?
There are CRTs that naturally have a second RGB input option available. Good example is Sony BA-1 chassis. For these CRTs, no muxing is needed, just feed the RGB signals to the second RGB input using the appropriate resistors and enjoy!
Where to source the 5V?
Before we answer this question, from usability perspective, below are the possibilities.
|Automatic switching||Manual switching|
|Mux mod with 5V from console||Mux mod with 5V sourced from the CRT||Traditional mod with 5V sourced from the CRT|
For all the above scenarios, you have to be in the correct video input where your
sync signal was fed into.
I highly recommend automatic switching. Less messy and straightforward to use. In case you need manual switching, you should go for
Mux mod with 5V sourced from the CRT option. I would avoid
Traditional mod with 5V from the CRT at all costs.
Applies to automatic switching. Make sure to source your SCART cables from reputable vendors. Make sure to double confirm you are only getting 5V from PIN 16 on your SCART cable. If the cable was mis-wired or you are using a modded console that outputs a voltage higher than 5V on PIN 16, then you can fry your chroma chip. That will be the end of your CRT. If you have a lower voltage on PIN 16 (like in the case of gscartsw), then blanking will not work.