According to Peter Grimshaw's books Hymas(Hydrauliske maskiner) were a Norweigan firm dating back to 1904 that was involved in cconstruction equipment from 1955 originally specialising in tractor or truck-mounted cranes, hydraulic backhoe attachments and dental chairs.
Hymac offered the 7.5t '82-R' crawler excavator of 3/8 cu.yard capacity "throughout the 1980s" and was upgraded to the 8200.
Apparently from the late 1960's to mid 1980's they built hydraulic backhoes for Bolinder Munktell/BM Volvo.
In 1990 the company was renamed Hymax A/S and the 'Hymax' name used on the upgraded 8200 which was replaced by the 840 and joined in 1993 by the 8.7 t 1990.
Apaprently Hymas stopped building their own machines in 1997 and are now an importer/dealer for other OEMs:
https://www.hymax.no/