Dan has likely hit on the problem: a machine with heaters for 440v input, but now running on 220v. Since the current will roughly double when the voltage is cut in half, the heaters think that the motor is drawing too much current, and they open the circuit to protect the motor windings from overheating.
The "pop" you heard was probably the magnetic contactor on the motor starter dropping out when the heaters cut the circuit to the magnet winding. Which is exactly what it should do when the heaters sense an over current to the motor. The heaters are automatic reset once they cool, although the control circuits are usually designed so that the motor will not also automatically re-start, which could be dangerous, so a motor re-start requires the machine operator.
If you have trouble identifying the correct heaters for your motor starter, post some photos of the inside of the electrical cabinet and of the nameplate on the drive motor. The charts for the heaters from the various manufacturers (General Electric, Allen-Bradley, etc.) are online, but they can be a bit confusing to decipher, especially if you're not familiar with them.
Typically, when the input voltage to a machine is changed, three things must also be changed: (1) the heaters [typically two on the motor starter on older machines, but three on newer ones]; (2) the connections to the control circuit transformer [usually a diagram is present on the transformer ID plate showing how to make the connections depending on the input voltage]; and (3) the motor winding leads.