These are the possible reasons and solutions:

• When you use the test button it will only do the voltages that you have set - when you use coins, sometimes it is on the hard grab turn waiting to win.
• On some PCB boards, there is a separate relay/switch on the PCB board that carries the hard grab voltage that can burn out due to higher hard grab voltages - even though it is a bigger relay.
• On some PCB boards, this is the big plastic relay with a metal device that holds it in place. If you have the board type with plastic relays, this is easily removable and replaceable (request a hard grab relay), otherwise a new PCB board is required.