• We can't have nice things.

  • by TIhde

I'm so bad, I should be in detention.

Oct
8

Repairing my repairable C64 power supply

In which the author discusses the very simple repair of his repairable power supply.

Well, I'm back from the Real World (patent pending) again, with enough time for a quick update. I had a repairable C64 power supply kicking around that had its 5 volt regulator go bad.

Rather than source parts & replace the regulator with an overpriced part, or a cheap, deadly replacement, I decided to go all-out and replace the whole 5 volt circuit with a DC to DC step-down circuit, regulated to 5 volts. Much more reliable.

 I sourced a part off of ebay, for a whopping $1.59 (shipped) from China. I know, I know - but the part really is that cheap.

Pretty pictures right here.

 It took all of 5 minutes, unsoldering 4 wires from the old board, and soldering them to the new board. Even I could do this and not mess it up! The board even came adjusted for 5 volt output - super sweet!

 I am now load testing it, and it appears to be stable & lovely.

 (For the curious; yes, I used repair(ing) / repairable repeatedly on purpose. It's my gift to the Department of Redundancy Department. I'm told they watch this blog).

Other than this, not much to say, as I've been very busy with life in general. I'll be around, promise!

UPDATE: *SIGH* We really can't have nice things. Already there seems to be an issue, so I'm going to do more testing and see if I can't figure it out. Under load the replacement starts heading towards 0 volts...

FURTHER UPDATE: Looks like I may have a bad converter, or else I'm missing something. I have another 2 from a different seller on order, and will test further when they arrive. It also occurs to me that perhaps the C64 is having some sort of issue with the high frequency the converter uses, and perhaps that's why it isn't working properly. I sure hope that's not the case, as these would be perfect to use instead of rectifiers (IMHO).

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Responses

Shark 11/5/2012

Is the replacement converter rated at 7 amps or better? It could be that the load placed upon it might be causing it to slowly shut down due to the current draw being above what it's rated to handle.

http://www.zimmers.net/anonftp/pub/cbm/schematics/computers/c64/c64extps.gif

This is the closest schematic that I can find for the old-style repairable power supplies. You can see that the regulator is actually a power transistor with 300 ohms connected to the base for power regulation.

Any chance you can get a few more pics of the original power supply components?