Info about Z80 machine

It is a normal-siced circular DIN connnector, the same size as normal audio DIN connectors. It has 5 pins, arraged as a square with one i nthe middle -- a quincunx, hence my name for it. I have also seen it called a '5 pin DIN plug Form C', a '270 degree 5 pin DIN plug' and a '360 degree 5 pin DIN plug' The other 2 5 pin DIN plugs, i nthe same size hosuing are : 'Form A' or '180 Degree' -- the one used for nost audio connections, IBM PC (5150, etc) keyboard ports, all DIN sockets on a TRS-80 Model 1, etc. This is the one the 3 pin plug will fit, and the one that will go into a 7 pin socket. 'Form B' r '240 degree' -- the one that was used for original CoCo Joysticks. And for the PSU/remote control conenctor on old Philips cassette recorders. This one will go into a 6 pin socket. The standard socket does, indeed, have 2 grooves, adn there is the nromal 'bump' in the housing to engage with a groove. There is also a slot cut in the metal housing at a positon 90 degrees from the locator groove. The plug was originally (?) used for headphones. The wiring was to put the left chanel on one pair of diagonally opposite pins, the right channel on the other. The centre pin wasn't used (or maybe screening). Turnign the plug over simply reveres the pahse of both channels, which has no audible effect. I belive the outer housing of the plug operated a switch in the socket to cut out the speakers when the headphoens were plugged in. If you turned the plug over, the notch in the housing lined up with the switch actuator which therefore was not operated. So the speakers stayed operational. What I do not know is why nobody ever made a socket for this plug with only one notch so that it couldn't be fitted upside-down. -tony