The repair I'm describing here involves mains voltage, which can be very dangerous if not handled properly.
Do not even think about trying this yourself if you are not absolutely sure what you are doing!
The original power supply of my C64 was broken. Unfortunately it was one of those power supplies where everything inside the case has been glued into one big block filling the entire case. Repairing such a mess seemed next to impossible.
Knowing that the power supply had one of those inefficient linear voltage regulators, I did not actually consider removing the glue from the circuit and actually repairing the old power supply. I still wanted to have a power supply that looks like the original one, though.
So I decided to remove the block of glue from the case.
Using a screwdriver to loosen the glue from the case and then (gently) smacking the case onto the floor allowed me to remove the broken circuit without destroying the case.
Now I had an empty case, ready to be filled with a new power supply.
As I wanted to avoid working with mains voltage as much as possible, I decided to use a transformer, just like in the old power supply, but instead of using a linear regulator to get the 5 volts required by the C64, I chose to use a switching voltage regulator (LM2576). Another reason for using a transformer were the 9 V AC the C64 requires for its real time clock and for some external extensions.
My circuitry is rather simple, consisting of a 36 VA transformer with two 9 V AC outputs with 2 A each. I have protected each output of the transformer with a slow 2 A fuse. One of the two 9 V outputs is directly wired to the output connector, the other one is going through a recitifier and a 2200 µF capacitor. At that point I have about 13 V DC which the switching regulator reduces to 5 V, without producing much heat. The switching regulator circuit is based on the example circuit that can be found in the regulator's datasheet. At the output of the regulator I have connected a LED so one can see if it is powered on. The 5 volt output is then routed to the output connector just like the 9 volt output.
I have drilled a small hole into the case for the new LED.
The new circuit with the transformer fits nicely in the old case.
The total power consumption of the C64 with my new power supply is a little over 8 watts. The power supply does not get noticably warm, unlike the old power supply.
The repaired power supply looks almost exactly like the original one.
Using a screwdriver to loosen the glue from the case and then (gently) smacking the case onto the floor allowed me to remove the broken circuit without destroying the case.
Now I had an empty case, ready to be filled with a new power supply.
As I wanted to avoid working with mains voltage as much as possible, I decided to use a transformer, just like in the old power supply, but instead of using a linear regulator to get the 5 volts required by the C64, I chose to use a switching voltage regulator (LM2576). Another reason for using a transformer were the 9 V AC the C64 requires for its real time clock and for some external extensions.
My circuitry is rather simple, consisting of a 36 VA transformer with two 9 V AC outputs with 2 A each. I have protected each output of the transformer with a slow 2 A fuse. One of the two 9 V outputs is directly wired to the output connector, the other one is going through a recitifier and a 2200 µF capacitor. At that point I have about 13 V DC which the switching regulator reduces to 5 V, without producing much heat. The switching regulator circuit is based on the example circuit that can be found in the regulator's datasheet. At the output of the regulator I have connected a LED so one can see if it is powered on. The 5 volt output is then routed to the output connector just like the 9 volt output.
I have drilled a small hole into the case for the new LED.
The new circuit with the transformer fits nicely in the old case.
The total power consumption of the C64 with my new power supply is a little over 8 watts. The power supply does not get noticably warm, unlike the old power supply.
The repaired power supply looks almost exactly like the original one.
