The early solid state games don't have the same extent of self-diagnosis as post '85 games, but there are tests programmed allowing a technician to check all the score displays for function, see if any 'feature' bulbs (or by this time their sockets) have failed, check for audio, operate all the solenoids and finally operate each playfield switch to verify the correct inputs from the grid or 'matrix' that they're arranged in. What's lacking is much, if any, facility to highlight a fault, such as 'Check Switch #', or 'Ball missing'. The electronic side of a Space Invaders pinball is far less complex than an Addams Family or Theatre of Magic, but uses many long-obsolete components. These can be pricey now, if available at all.
But of the early systems, Bally are generally thought to have had the most service-friendly. The Mpu board runs a check on those outdated parts when switched on, showing its progress (or not) with an on-board l.e.d.
Even 40 years on, in some ways that usefulness seems to have helped. A large number of surviving machines resulted in modern 'Alltek' replacement circuit boards. Costly, but the main Mpu board can be used for almost any '77-85 Bally game simply by altering setting switches; not even original program chips are needed.