First thing I would do in this instance is slide out the mech, and clean and examine all the contact sets, and the multi-plug/socket arrangement for loose pins.
Do you have an AVOmeter? With the mains off, you could check continuity of the arm release solenoid, using the Ohms range; then, with mains on and coin accepted, check for voltage at the solenoid.
These machines fall between the 'penny slots' category, and the 'electro-mechanical' era. Neither enthusiasts group fully accepts them.
I've had useful hints from the MPU people: https://www.fruitemu.co.uk/ib/