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PWM/Power control issues

Looks like I'm another person struggling to get PWM control over output power. Bought second-hand  K40, "Type 2" LPSU (pins instead of screws for cable connection) with MG3 controller. Using Lightburn, laser outputs when moving as a part of cut, but not when repositioning as direct command. Reinstalled MG3 to ensure it was all correct, replaced PWM wire with ground-shielded cable. Laser outputs at full power (~25mA) no matter PWM setting.

  • Grounding has been ensured as much as possible (my K40 was one of those lovely ones with plastic washers on the grounding connections, so I changed that ASAP!)
  • MG3 is outputting PWM signal, however it is a very weak signal, built on ~5V bias.
  • Have tried using a pulldown resistor across PWM IN and GND (tried both 10k and 510k resistors, no change) to remove the 5V bias, no change to behaviour
  • With IN pin not connected to PWM, floats at 1.75V
  • With PWM pin not connected to IN, floats at 5V
  • Wiring (especially LO cable) has been checked and is well connected.
  • LO goes to 0.25V when lasing, 5V when off
  • Have checked and confirmed all GRBL settings are correct
  • Have reflashed MG3 to ensure firmware is up to date

Any suggestions about how to get this all working? I'm starting to suspect the LPSU is where the issue is, but the fact the MG3 PWM pin is outputting the biased 5V PWM signal makes me concerned the issue could be there.

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