C64 PSU died?

MIDIbox SID
1

When testing my C64 PSU I read a stable 5.24 V on the 5VDC lines. The AC-lines only give 3.2 V, but should be delivering about 9V. I know the PSU did deliver just a bit above 9V when testing it for the first time, so therefore I reckon that something must have died..

Since it does give some voltage on the VAC-line, that gives a little hope. On the other hand I have the ‘brick’ PSU version (the square ribbed one) that came with a C64C and also has no access to the fuses from the outside (not that I would need that right now, since a burnt fuse would give me 0VAC, right?). There seems no option to open the PSU, except for brute force :wink: As I don’t want to waste a lot of time with a screwdriver and hammer to open it up and then discover that there’s nothing to repair inside, I need some advice.

Is this type of PSU also filled with epoxy and therefore unservicable? In other words, should I throw this one away and find a new power supply?

2

Are you measuring 3.2V on the AC lines using AC setting on your multimeter?

If so, there’s not much hope fixing this PSU. Internally, it’s just a transformer with two 9V AC secondary coils, one leads directly to the output pins, the other goes through a bridge rectifier/voltage regulator to supply 5V DC. I’m no expert but getting less than 9V AC on the AC output pins suggests a short somewhere on that coil, i.e. less coils, less output voltage. As far as I know, fuses either pass all the voltage or burn out and pass nothing, not drop the voltage.

3

The 3.2 volts are indeed measured with AC selected on the multimeter. Thanks for your information about the internals of the PSU, I’ll better spend some time looking for a different PSU, instead of trying to fix this one.