Always measure voltage on the PCB side of the JAMMA edge and always with a board connected. If you turned on the Sigma without a board connected and measured 5V, you’re probably getting much less at the board when you do finally connect the Jamma harness because without a board connected, there is no draw on the power supply.
- Turn on the Sigma with no board connected
- Check voltage at the JAMMA connector and adjust to 5V
- Power off sigma then connect a board
- Power on and measure voltage on the JAMMA edge of your arcade board and adjust to 5V
Do this every single time you switch arcade boards as each board has different current draw.