Building a C64 Saver Kit
The C64 Saver is a device that is placed in between the power supply and the computer on a Commodore 64 or VIC-20. With the age of the power supplies, they can fail in a way that the DC voltage, normally 5 volts, can go over 5.5V and destroy the unprotected chips in the computer.
This is a walkthrough on how to assemble this from a kit, in particular, for those who have purchased the kit from my store available here. It's also available fully assembled.
This is a great design by bwack, so many thanks to him for providing this as open-source. I've tested the response of this design and when the voltage crosses the shut-down threshold, normally around 5.4V, the output voltage instantly drops to 0. There is no spike, nor any delay. I'll be making a video demonstrating this shortly.
Find a nice way to hold the board, and let's install Q1, the MOSFET, first. I use lots of flux, tack down the chip by its little feet, then heat the edge of the sink at the top and wait for solder to wick down using high heat.
I plan on making these PCB holders for sale.
Soldered in. Clean up all that flux!
Next, I place all the components in this 'row' as they don't interfere with each other underneath. Also note that some resistors are 1/4W instead of 1/8W, so I install them so one end is touching the board and the other is up. It works fine.
Splay the leads out sideways, but be careful as a few need to go 90° instead so they don't aim towards another solder point.
Once they're soldered in, trim them.
Repeat with the remaining resistors.
Finally, take some of your trimmed leads and use them to make a jumper in the two rows of empty holes. There are 8 holes, and the jumper has to go from the 4th to the 5th hole on each side. This allows the 9V to pass through.
Next up, the DIN plugs! This is the end that goes into the Commodore. To get the sheath off, bent the little tab down into the center of the plug, then stick something inside from the 'wire end' to push the fitting out. It's tight!
Here you can see the pins where the wires get soldered. Notice the gap at the bottom where there is no pin. Use this to orient yourself when selecting the pins to solder, it's easy to get mixed up.
Notice that I'm using the other DIN connector to hold this one. This is because the heat from soldering will actually allow the plastic to move the pins slightly, causing them to be off-center or worse, loose. This works well to keep them in place.
9VAC go to either side of the gap. Ground goes straight UP from the gap in the center pin, and 5V goes to the right of ground in this view. Ensure they can't touch by putting a little shrink wrap around the ground pin. The rest are safe.
After twisting up the wires, I usually put shrink wrap on but only shrink the ends to leave a nice finish.
Bend the tab with the crimp area towards the center and put both metal fittings on before you crimp the wire in place. If you don't have the fittings in place when you crimp, the tension pulls the plug crooked.
Now let's move onto the input DIN.
We don't need the two pins beside the 9VAC. So, take a set of small pliers and gently untwist the exposed end of the pin, and it will easily push out.
Et puis, voila! I also bend the pins a little to make more room. You will notice that I have 5 pins here instead of four. Occasionally, a power supply will have power coming in on the wrong pin. To accommodate, the early units could take power on pins either side of the ground pin. Since I don't know where the power pin is, I run two wires from both and join them at the board. If you can determine which pin has power from your supply, you'd only need one wire and could remove the additional pin.
Done! Ensure they can't touch by putting a little shrink wrap around the ground pin. The rest are safe.
Here we see the fittings in place before crimping.
Once they're all done, connect them end to end and test with a meter for continuity.
Connect up the harnesses to the board, paying CAREFUL attention to the IN text on the front of the board (seen in the next picture) which goes to the female plug. I usually solder the wires directly into the board. However, you may have the blue wire connector blocks that you can choose to use. I find there is more room to finesse the wires into the proper length by soldering directly to the board.
All done! Let's test it before installing it into the case.
Note the IN beside the 9VAC. That's the side that goes to the female DIN connector (and to the power supply).
It's passing 5.3 volts through the unit just fine.
I'm using an adjustable bench power supply. If you don't have one, try plugging in your Commodore power supply for this step. Measure the voltage at the 5V in and 5V out. The 5V out could be up to 0.1V lower.
I bumped the voltage to 5.5V and now it's not allowing any voltage to pass through. Great! This particular unit cut off at 5.43V. Due to variations in the resistor values, I've seen values from 5.39V to 5.43V.
If you don't have an adjustable supply, feel free to put ANY voltage into the saver from 0 to 20V DC. It MUST be DC of course, but nothing in this range will hurt the Saver if not left for an extended period of time. I guess I should leave one at 20VDC for a while and see what happens!
Alright, let's install the saver in the case. This parts easy, just make sure the holes for the case are visible in the board. Note that I'm using Robertson screws. It's come to my attention that these are a Canadian Thing™ and nobody else seems to have them. They're by far the best kind of screw, and I can't imagine building a house with Philips. 🤮
On the back, put in the longer screws, all the way in WITHOUT putting the top on. The screws will start to tighten up, but keep turning so they intentionally strip the holes in the board. You want them to be able to turn freely in order to tighten the top lid down properly. Then, back them out so they're not protruding past the board.
You can just see the screw tip sticking up through the board. That's what you want.
Put the lid on and screw it down carefully. Only tighten the screws enough to pull the two halves together cleanly.
When I ship these out, I test them carefully and even test it on my own C64!
I hope you enjoyed my writeup on how to build a C64 Saver. Please favorite my Etsy store so you'll be notified of new products, and check out my Youtube channel and other links.
All the best, Jason