CFM - Computer Field Maintenance  


The SWTP (South West Technical Products) 6900 was the first computer I reaaly got to know well and I learnt Assembler programming and the basics of comuter and CPU operation.   I also repaired them on site for customers like Imperial Collage in my job as a mobile engineer for CFM (Computer Field Maintenance).  6800 Programming Guide

The design used the Motorolla 6800 microprocessor and the new S-100_bus architecture.

I spent many an hour in the workshop also loearning the Flex operating system and programming BASIC to read/write with floppy disks


I can't say that I spent as much time on the now (fairly) famous Altair but we had one in the workshop a few times. it also used the S-100_bus architecture

It was on this machine (or possibly the very similar MITS machine) that I first saw the "amazing" computer game of Star Trek!

It's running in the video here and the pre-graphics text based play is something to behold

I also worked on the Cromemco System Three, which had  7 imch floppy drives with an amazing auto load/eject mechanism... I probably spent more time reparing that, than anything else!



I learnt the CPM operating system on the Northstar Horizon system, which was Z80 nicroprocessir based. CPM was very like DOS, which would later appear on the IBM PC


I came into computer engineering just as the Z80 and 6800 based systems appeared but my company, CFM, had also been maintaining mini comuters for some time and went on a week long course on TTL logic and CPU architectures. We trained on the DEC PDP 8E, which required you to load a series on memory locations with the binary codes for the boostrap wi the front panel switches... just to grt it started! 


Being a mimi computer (pre CPU chips) the Central Processor consisted of discrete electonics on two boards in the chassis. I partnered a very experienced engineer on site and we once repaired this logic on a malfunctioning unit wiht the aid of an oscilloscope, circuit schematics and soldering iron!


I also went on field service calls on the Molecular 18, Sadie and Susie systems,  al British computers




Quite amazingly, we also maintained the LEO computer at NPL (National Physical Laboratory) in Teddington. The LEO (Lyons Electronic Office) was a very ealry British system built with valve (vacuum tube) technology.

Lyons were famous for their tea shops and had so many in so many locations, that they developed their own electronic computer to run the business tasks, like stock deliveries and payroll



LEO Instruction Set