Machine was offered at such a low price that it was bought unseen.
Fortunately, "plan B" or making it a spares machine was not necessary. The game
proved to be in very nice state. The CPU board needed a 555 chip for display
interrupt generator, and some connectors were a bit dirty. But the game booted
the first time power was turned on, with no problems whatsoever. Manuals and
instruction cards were inside!
The playfield has been mylared when new. That helped against the worst problem
of these Ballys, playfield paint wearing. The game needs only cleaning and waxing,
and new rubbers. Even the backglass is completely intact. There are some scratches
in the cabinet, but that's OK for a game of this age.
Frontier has worked just fine for a long time. But now there is a problem. It doesn't start!
OK, open backbox and look at the diagnostic LED, how many times it flashes. What, it doesn't light
at all! Take the multimeter and check voltages... the +5V is missing. Problem was not in the
regulator or rectifier, but in the rectifier board J3 connector. After some wiggling it works again.
But the connector should be replaced as soon as possible, because otherwise the problem will surely reappear.
I removed the suspicious looking memory backup battery from CPU board, and installed a gold cap in its place.
No more worrying about leaking battery destroying the PC board.