The text on the PCB says "ADC BOARD", I suspect it is a multi chip module with a fast Analog/Digital converter. The right side looks like a number of analog circuits and with all the trimmers along the side it definitely looks analog. The +/- 10V also says analog.
The sensor connected to the metal is probably a bi-metal temperature switch, turning off the system or sounding an alarm if it is close to overheating.
The board looks like the right age to have fully plated conductors under the solder mask.
Cool looking module!
Göran