• May 29, 2024
Commodore 64 Computer showing keyboard and label

Restoring a Commodore 64 – Part 1

Commodore 64 computers were the most popular and best selling computer – in the 1980s. Easy to setup, 8-bit processor, floppy drives, sound chips, games on cartridges, joysticks, a mouse, cassette tapes for cheap program storage, programming books, a graphical interface, modems, hard drives, etc.

Before the 8088 PC took off, before Windows, and a least decade before I would buy my first 486. When I was a kid, I was trying to figure out how to program in basic on a Commodore 64. With a thick programming guide, a cassette tape to save the program, and an orange on black monitor, I spent hours (days?) trying to create a simple text editor to write school papers. Never mind that I didn’t have a serial printer. When all else failed, there were a few math games on tape. Good Times!

Eventually, I had moved onto windows 3.1 on a PC. Then came win 95 and, eventually, win 98 on a 486, the internet happened! So did the 800 mb hard-drive, better VGA graphics, and sound baster audio, etc… And, the commodore was struggling to turn on due to power supply issues. It needed to be “hot plugged” into the power to make it boot. It also didn’t connect to AOL. The new fast 56K dialup made it beyond obsolete. About 25 years ago, I put it on a shelf and forgot about it.

Spring cleaning 2023, I pull a pile of random cables, old network switches, and a few floppies off this now tan colored Commodore 64 computer. Turns out 20+ years in the basement dust helps collect a little moisture, that leads to little mold growth and that causes a very ugly looking plastic case. It was a cold and rainy day – perfect for indoor projects. A bit of soap and lots of scrubbing… the computer was looking good. Opening it up… the inside looked okay too. The restoration project had started.

Start with the cables:

At some point the video cable had become damaged. Naturally, the RCA jack was ripped off the end of the composite video cable. I had also tossed out the antenna/game coax antenna adapter a few years ago (along with the VCR). The floppy disk drives have long since been lost. The cassette tapes looked workable. I found a few original power bricks (white and black type), a RS232 adapter, the IEC serial extension cables that presumably went to the floppy drives, the orange & black CRT monitor is still on the self.

This computer has 5 pin connector: 1 – Luminosity, 2 – Ground, 3 – Audio Out, 4 – Composite Video, 5 – Audio In. That goes to RCA plugs. After rebuilding the RCA cable ends, I had to find something that accepted a composite video. Turns out the new LED DLP pocket projector included a cable for this purpose – incredible. And… Naturally, the computer didn’t start when I plugged it in. I got a red power light. Blank Screen. Maybe the entire cable is bad?

Next, try the coax RF cable. These computers output a composite video and a RF signal on either channel 3 or 4. The RF signal has now been rebranded as NTSC and the signal doesn’t work on the ASTC encoded frequencies (which are all of my new DTV’s – not that I would trust this plugged into my new TV). Fortunately, I had an older pre-ASTC television and antenna cable in the garage. And… nope… no picture. Just static…

Power Supply:

The internet is covered in stories about how the original C64 black epoxy-filled power bricks go bad and send a high voltage on the 5 volt DC power line. Turns at this probably was starting to happen to this one. Only it was a newer white power brick that was putting out 5.7+ volts DC. Now… that isn’t that high. But, it wouldn’t boot unless it was switched on first and then the power was quickly plugged in. Meanwhile, the other black older power bricks I still had (the ones the internet was warning me about) were working perfectly well. Still it wouldn’t boot.

Chips:

If the power supply went bad, it could damage just about anything. Most people reported that the ram chips were damaged in the high voltage. But, these ram chips weren’t getting hot at all. The CPU was getting warm, the rom chips were a bit toasty. And, the voltage regulators were on able to burn you in an instant. They clearly needed a heat sink.

More comments on the internet point to: The PLA chip is likely bad. They tend to die in the older systems. The programmable logic array is the main switch that control what goes where on the bus. It is the center of everything.

So… I ordered a Dead Test Cartridge from eBay to test the system, a new modern PLA chip, and 8 new ram chips (which are still in production). Now we wait for part 2!

Commodore 64C vs Silver Label:

Meanwhile, this computer has a white fancy-more-modern looking case. This should be Commodore 64C from after 1986. It should have one of the more modern “short” boards in it. However, something was off.

The board itself had fancy looking gold colored ram chips. There is a paper label on one of the chips (the PLA or programmable logic array). The board didn’t really seem fit in the case’s mounting screws, the metal shield was pressing on the circuits (likely causing a short) and not a single one of the heat sink cover arms were touching a chip correctly. The board also says: “ASSY 326298 REV C 1982”. And… it has a very old style shielding.

Inside a Commodore 64 computer, circuit board, showing rows of chips.  Top row chips : 2 CIAs, basic rom, kernel rom, character rom, video ram, cpu; row 2: reset chip, 4 ram chips, switching, addressing, logic, PLA, SID, VIC; row 3 chips: reset chip, 4 ram chips, ram switching, addressing, 2 logic chips.
Power supply and clock circuit on the right
Commodore 64 board, removed the cover, keyboard, and video/clock shield cover.

It took a lot of research looking around on the internet, compared photos at vintagecomputer.ca and did a little detective work on the dates. This would likely be one of the original computer boards, from in the earlier days of production. The video chip is a MOS 6567R56A 2083 (one of the older generation). That was apparently manufactured week 20 (May) of 1983. The internals are a few years older than the case. Wonder how this happened? However, there isn’t the matching case with a serial number to confirm. This board could have come from one of the early silver label machines? Maybe? I will never know…

According to the forums, these old style boards were prone to having issues and many were replaced under warranty. Over a decade of production, Commodore continually updated the chip layout and board design to make it more efficient, cheaper, and less prone to problems. For example, the clock circuit was replaced with a single chip, the video chip was upgraded, and memory banks reduced.

Link to Manuals | Link to Jameco to Buy Chips