Hi all,

Newbie here, I think I've run up against my first major pinball issue.

Stern "pinball" 1977 solid state, good working condition until today. Found the machine powered on, but unresponsive to anything. Reset the power switch and now experience:

Rapid continuous clicking on the solenoid driver board (as 2518 22 A3)
Steady green LED on the MPU
Holding the flipper buttons in results in continuous firing of the flipper solenoids.

I've checked all fuses, and dont see anything else out of the ordinary on any of the boards.

Any thoughts on my next troubleshooting steps?

Looks like MPU has been worked on, had acid damage at some point. Will check voltage on rectifier, it also looks new-ish.

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Removed? I see some brackets above the knocker

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Alright, finally had some time to devote to this.

Checked all test point voltages on rectifier, solenoid driver, and MPU. All values within specs.

Checked and reseated all pinned connections. All headers and lines are clean, likely replaced at some point, no cracked solder visible anywhere.

Removed all socketed chips except for U2/U6, U9, and U11. This stopped the clicking on the driver board, but still had steady green on the LED on the MPU.

Reinstalled socketed chips, clicking is back, steady green.

Suspecting an issue with one of the U2/U6, U9, or U11 chips.

Thinking it might be time to try a replacement MPU from Alltek and hope for the best?

Well, went ahead and ordered the Alltek MPU and SDB. Received yesterday and replaced the SDB first. That stopped the clicking and continuous firing of the flippers when the button is held down. Still had no flashes from the MPU LED, just a steady green. Replaced the MPU with the new Alltek and fired it up.

Great success, whatever the issue was it's been resolved and the game is back to normal now