The power of the RD 644xs engraving machine cannot be adjusted after replacing the laser tube

Use a multimeter to measure the voltage at the laser output port on the control board. Set different power levels and check whether the voltage value changes accordingly. It is recommended to test at 1% and 90% power. At 90% power, the output voltage should be between 4.0V and 4.8V; at 1% power, the output voltage should be between 0.1V and 0.9V.
If the voltage at the board's laser output port is within the normal range, the issue is likely related to the laser power supply of the machine. In this case, please contact the equipment manufacturer for further assistance.