Addendum: This happened earlier. I only got to write it down around Feb. on 2019.
Wow. I’m excited. I bought a C64 on eBay:
C64 Bread Bin Assy 250425
2019-02-03, 21:55:34
Fixed price: 69.00
Shipping: 5.80
Power adapter
The device arrived in a few days. Before I did anything with it I opened it. It looked in very good condition inside.
I tested the power supply first. At first I didn’t measure anything reasonable. Then I realized that the outer ring of the DIN connector is not ground. With the right GND pin I was able to measure 5V. But I still had problems with the 9V. I only found out much later that the two 9V pins have no ground reference. That means you just have to measure the voltage between the two pins. So far that was ok.
First try
I then connected the C64 to an old TV set using an antenna cable. First, I familiarized myself with the channel search. I just wanted to turn on the C64 for as little time as possible. I.e. I looked up the frequency from the internet and tuned the TV to a frequency close to that. Then I turned on the ’64. The power LED came on. But it was suspiciously dark. I then searched for the station and found it pretty quickly. Unfortunately only a black picture. 😩 Unfortunately, that wasn’t a good sign.
I then opened the C64 back up on my workbench and this time measured the voltages while it was on. It immediately became clear that something wasn’t right. The 9V were ok. But the 5V line has collapsed to 2.5V.
After googling for a while I had a better understanding of how the power supply works. The 5V DC and 9V AC are completely separate voltages. I was very lucky overall. On the Internet you can find many reports that the power supply easily breaks with age. Most of the time, however, it delivers too much voltage on the 5V rail. That case can damage the C64 (the RAM chips).
I then cut the 5V line on the cable and soldered a connector onto it to which I could connect my bench supply. First I had to move the old TV monstrosity to my office. The cables were a bit short, but reached eventually. Then I set the power supply to 5V and started with 500mA current limit. After switching on the C64, the current limitation started immediately. I turned it up a bit until it ran normally at about 800mA. Well at least there seems to be no short. At first the screen was black. I thought to myself – oh dear – there’s something worse. But due to the initial current limitation, it certainly didn’t start up properly. Turned it off and on again. And HEUREKA – a blue screen with a blinking cursor. Fantastic it was alive. 😄
It’s alive!
I was happy to type in a few simple basic programs. MY son watched me and immediately started typing things. He typed his name and some of his kindergarten friends. It was unbelievable how quickly he was able to type.