ZX Spectrum +3 RGB Cable

I have an RGB cable for my Spectrum +3. This allows me to plug the Spectrum into a Commodore 1084s monitor (or one of the many many clones). I have three of these in my house and two of them contain a 9 pin D-Sub RGB port. Making the cable was fairly straight forward once I’d found the correct pinout for the monitor and the Spectrum. If you try and make one yourself, beware the +3 has a different RGB port pinout than the Spectrum +. Here are the pinouts for the connectors:

Commodore 1084d & 1084dS  Analog/Digital Connector
9 PIN D-SUB FEMALE viewed at the monitor

  _____________
  \ 5 4 3 2 1 /
   \_9_8_7_6_/

Pin  Name    Analog Mode     Digital Mode
 1   GND      Ground          Ground
 2   GND      Ground          Ground
 3   R        Red             Red
 4   G        Green           Green
 5   B        Blue            Blue
 6   I        not used        Intensity
 7   CSYNC    Composite Sync  not used
 8   HSYNC    not used        Horizontal Sync
 9   VSYNC    not used        Vertical Sync

This was taken from this website here. The ZX Spectrum +3 RGB/Peritel port has the following pin configuration:

VDU Monitor

The +3 can use a monochrome or colour VDU monitor (or a French
standard PERITEL TV) instead of (or in addition to) an ordinary TV. If
the monitor that you wish to use isn't quoted as being Spectrum +3
compatible, then the chances are you'll have to buy a lead for it
(contact your Sinclair dealer).

A VDU monitor (or PERITEL TV) should be plugged into the RGB/PERITEL
socket at the back of the +3.

PIN	FUNCTION
				      RGB/PERITEL socket
1	+12V				    __   __
2	GND				  _- |___| -_
3	audio out			 /  7     6  \
	______________			/   o     o   \
4	composite sync			| 3    8    1 |
5	+12V				| o    o    o |
6	green				\  5       4  /
7	red				 \ o   2   o /
8	blue				  -_   o   _-
					    `-----'

When using a monitor, some provision may have to be made for sound (if
required). If the monitor has an audio input, then this should be
connected either to pin 3 of the RGB/PERITEL socket or to the
TAPE/SOUND socket at the back of the +3. If the monitor is not capable
of producing sound, then an external amplifier will have to be
used.

This is from the excellent World Of Spectrum‘s copy of the ZX Spectrum +3 User Manual. Remember when manuals were actually worth reading?

All I did was connect the R,G,B pins in the Spectrum to their equivalents in the Commodore monitor’s 9-pin D-Sub, and then connect the Composite Sync from pin 4 of the Spectrum to pin 7 of the Commodore. On the back of the monitor are several buttons to choose the type of input signal, eventually I found a combination that produced an image.

The sound comes from pin 3 of the +3′s RGB port and I simply soldered a short RCA plug to the wire on that pin and brought it out the side of the plug. Since I didn’t have a suitable casing for the connector I used the hardware hacker’s favourite – hot melt glue, plus a few bent paperclips to act as strain relief on the soldered connectors.