Hi David, did you find a manual ? I also need one for a similar unit I just acquired (Model 5042). It seems they were originally sold under the brand of 'Prism Electronics' of Cambridge, but this changed to 'Prism Instruments', and the model numbers were changed. Another company, Tinsley Instruments, may also have been involved. I've spoken to folk at both companies, but due to the age of the units, they were unable to find any documents or assist with other info. I've uploaded some pics from the sales leaflet to this post, this has a sticker on it showing Tinsleys address which they moved to in 1991, so the units were presumably still being sold in the early to mid 1990's. There's some info on the IEEE488 support on the leaflet. I will continue to try and find further info and post up here if I find anything.
Andy McC, GB