It greatly helps to "silicon date" an appliance when after such insights. This is one of the first things I recommend when inspecting vintage gear, as much time & energy can be otherwise wasted on items that are just not worth it. Hence although you may have an "oldie but goodie",the chances are that power hungry TTL ICs were used if the gear is 1970s-80s vintage, & the associated heating may mean the device is inherently unreliable.
ICs have been in wide use for ~40 years, so even a casual look at circuitry should give a guide via IC maker date codes. This is of course traditionally in the YYWW style, so 8947 means made in the 47th week of 1989, & a current PICAXE could be ~0828. Don't get fooled with logic IC codes like 4046, 4011,7404 etc, which are NOT made in 1940 or 1974! Most usually include "family" coding anyway tp prevent this- 74HC04, 74LS00 etc. Stan