I assume you did get a step down converter if so what did you set it at,
Below is the minimum recommended power of the step down

Gamecube - 100 Watts

It is important that the power rating of the step down at least matches the power requirements of the console, so a 100 watt step down is the minimum requirement for a 100 watt console. However, I recommend using a step down with a power rating of at least 30% higher than the power required by the console. Nowadays, it is not worth buying a step down of less than 50 watts.

if the setting is lower than the minimum wattage needed the converter will blow, that may be what is wrong.