Commodore 64 External Power Supply, Part No. 902503-02

I have taken a circuit diagram by William Levak from Bo Zimmerman's website and made some corrections and changes. The drawing at Zimmer's shows a PNP transistor labeled "SK3052P" which I believe is in error and should've been a 3052P, which is a +5 VDC, 2A voltage regulator. NTE 1934 is an equivalent part. Moreover, I believe the original resistor is 30 ohms, not 300 ohms.

When repairing, I used a 3W resistor instead of the original half-Watt. The original diodes were 1N5400 (50 V), but I used 1N5408 which can withstand much higher voltages (1 kV) (see 1N540X datasheet to compare).

Photos and Images
  • My version of the schematic in png format is here (148 kB).
  • Photos of the exterior top, side, and bottom of the power supply enclosure.
  • Photos of the inside from the top here and here.
  • Photos of the top of the circuit board (with the 3052P regulator removed) here and here.
  • Photo of the secondary side of the transformer here, including an annotated version explaining the terminals here. Hand-drawing of terminals here. Additional transformer view here.
  • Photo of the original 30 ohm 2%, 1/2W, resistor. Units of top scale of ruler are metric, showing resistor body is roughly 1 cm long. Diameter is 0.15".
  • Photo of the bottom of the circuit board.

P. David Buchan

December 22, 2016