Sinclair ZX80 / ZX81 / Z88 Forums

Hello,

I am building a Harlequin 48K, and I want to only Video output I want to use is RGB. I haven't soldered any of the components involved in processing the RGB signal for Video Composite, but I wonder if I went too far with this.

My question is: are the R22 resistor and the C37 capacitor at the exit of the U29A gate (ComSync) required for the RGB only scenario?

R22 and C37 are only needed if you are going to use U48 (AD724) to produce a composite (baseband) video output.

If you only require an RGB output, these components do not need to be fitted:
Chip U48 (AD724).
Capacitors C22, C23, C24, C25, C28, C30, C35 and C37.
Resistors R22, R42, R49 and R50.
Y2 (4.433MHz crystal).
Connectors J7 (video output) and J9.

Note the above is for the revision G board.

Mark

Thank you, Mark. I knew I don't need most of the components you listed, I wasn't sure about C37 - R22. My board is indeed rev. G.

The note on the diagram show for NTSC / PAL:

J9,J10,J11
1-2 = NTSC
2-3 = PAL

As far as I am aware, RGB doesn't care about PAL and NTSC, so how to strap the pins on the J10 and J11 connectors?

valentin wrote: ↑Tue Nov 23, 2021 8:49 pm As far as I am aware, RGB doesn't care about PAL and NTSC, so how to strap the pins on the J10 and J11 connectors?

Not entirely true.

PAL is a colour carrier encoding system, but lots of people also mean it to mean a 625 line, 50Hz, 15625Hz video system.
NTSC means the National Television System Committee, which developed the analogue TV systems used in the USA including the black and white (monochrome) system that existed before they added colour.

Again, most people use this term to mean a 525 line, 60Hz, 15.734kHz video system (although note that some of these frequencies are slightly different depending on if it’s a monochrome or colour video system).

RGB can be either 625 line, 50Hz, 15625Hz or 525 line, 60Hz, 15.734kHz video. Hence J10 and J11 have to be set correctly in order for the video timing to be correct.

Mark