Shorted electrolytic cap across the switch. Shorted TIP-102 on the driver board. Bad TTL 7402/7408 on driver board.
Start at the solenoid and check/replace the electrolytic cap across the solenoid switch.
Next test the TIP driver transistor. Power off. DMM set to diode test. Black lead on middle leg/metal tab of associated TIP transistor. Probe the outer legs with the red lead. You should see .4 to .6v. If not replace the tip driver transistor.
Next test the associated 7402 and 7408 TTL ics. Power off. DMM set to diode test. Red lead on ground. Black lead touch the associated pins on the 7402 and 7408 ICs. Again you should see .4v to .6v. A lower or short is indication of bad TTL chip. Use the schematic on IPDB to find the associated 7402/7408 pins.