It's going into solenoid self test at bootup. Disconnect the cabinet switch connector J3 from the mpu board and see if it still does it. If it does, mpu issue. If it doesn't, coin door wiring issue.
Everything on a classic bally game is fixable, and even if desired all boards are available from multiple sources in multiple versions to replace.
The only thing that's odd is that if it were the coin door shorting the self test switch out, it should go to the lamp test first, then the display test, then the solenoid test. At any rate try the connector removal first (you can also remove J2 if you like just to isolate anything on the playfield causing it, but there's no regular switch on the playfield that gets you into self test)
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