I have a printed manual for the Nichiyu FBT10, 13, 15, 18P - 35 series which also incorporates the 18C as well. This model uses the SICOS 50 system. This model has an early style LE screen whereas mine was 5 leds shows battery status. Manual is dated February 1991 so you won't find this on the bookshelves any more !
If you want to see a few pages let me know or IF you want the whole manual then it is 'free' but plus postage costs to wherever you are, from Brisbane, Australia. Manual is A4 size, 15mm thick and weighs 500gms.
Trouble shooting flow charts, schematics, Adjustments, fault finding tips, Circuit diagrams.
Please only ask if it is your model that you are having troubles with.
I do have a pdf of mine which was the FBT15-30 Unicon series, now that is time travel hahaha.