IBM 5155 analogue display fault

Roughly, yes (although I've never worked on a Tractor...). I think of them as : Allen : Triangular wave rapped round a circle Torx : Sine wave rapped round a circle Bristol : Square wave wrapped round a circle Very approximate, of course (and certainly not enough to machine a tool to fit them), but it gives the right idea. The comment on the PSU applied even if the service call was totally unrelated to PSU problems, If an engineer came to, say, install some RAM chips, he was supposed to check the PSU screws (and some other things) and replace the PSU if necessary. This was, apparently, for safety reasons. IF the PSU had been opened, there was no way to know if any nasty bodges had been done internally... (FWIW, I've opened IBM PSUs, I've repaired them, IMHO, properly and safely, and I've put the tamperproof Torx screws back in again...) Well, my Father's Citroen BX (touch wood...) has hard very few hydraulic problems. I've had to replace just one high pressure pipe (to the back brakes), which was damaged by an idiot garage mechanic when he refitted the rear subframe after an accident repair. So do I, but then I have a Myford lathe, which is assembled with an interesting mix of BSW, BA, and metric bolts... 11mm is relatively common. It's 12mm that I find somewhat obscure, and which Citroen seem to use to excess... -tony