On Mar 20, 0:06, Glen Goodwin wrote: 6116? I don't have either the service manual or my ZX81 handy, so I can't check, but as far as I remember, just remove the 4118 and replace with a 6116. There might be a wire link to change (if so, it's obvious) but I don't remember having to do that. It is good practice to fit a socket, though. A few ZX81's had a pair of 2114's instead of the normal 4118, which were in short supply at one time, but the same principle applies (the PCB is the same). -- Pete Peter Turnbull Network Manager University of York