X-10 Mods - SC503 Maxi Controller

Here we explain how to modify a USA 115V SC503 Maxi Controller to operate at 230V.


I have successfully completed this modification four times, however, and I accept no responsibility for the effects of anyone making these modifications.   You follow these instructions at your own risk.

Modification Steps

To modify the Maxi Controller, follow the following instructions:

  1. Remove the four screws at the bottom of the unit and take off the bottom cover.
  2. Remove the screw in the middle of the PCB, and remove the PCB keeping the top of the unit on the tabletop.
  3. Scrape off the epoxy glue by the big blue capacitor being careful not to break the fuse wire.  Replace this capacitor with a 1uF 400-volt device.
  4. Replace the smaller capacitor with a 100nF 400-volt device.
  5. Remove the 22-ohm resistor, and stand it on end in one of its mounting holes; add another 22-ohm resistor in series with it.
  6. The 275-volt varistor has been soldered underneath the circuit board across the incoming 230V mains supply, but after the fuse.

This picture is pre-modification.


This picture is post-modification.

If you attempt these modifications, please let me know your results, and read the warning on the X-10 and 115V & 230V page.

Comments received at Redoak

  • In Jan 2009, Eddy Kok from Singapore confirmed the modifications worked.
  • In Feb 2010, I had a report from muzzag50 in Australia that the modification worked.
    ps - this is a really easy modification! John

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