I've recently completed a restoration that took quite a long time and has ended up being one of my most extensive restorations, a Commodore PET 4016 from 1980. This machine came from a trusted seller here in the Minneapolis St. Paul area from whom I have gotten several machines over the years, including the Apple II Plus machine that I've already covered on the bLog.
The PET machine was much cleaner than the Apple II, but both machines were in a non-working state when I bought them. As is usual for this type of restoration, step one was to take the machine all apart and clean it. In this case, I didn't take the monitor apart because it was cleaner and at least from the bottom appeared to be intact, but I removed the monitor from the base of the machine, removed the mainboard and power supply, and throughly washed and cleaned both the bottom housing and the mainboard. On inspection the mainboard showed alot of corrosion. There is corrosion at the top of the IC legs where they enter the DIP packages. If the package seals are broken, those chips will likely be bad.
This machine started life in a local Junior High and had some identifying marks on the side which I was happy to keep, but the students had picked at the front label. It was all tatty and so I removed it during the cleaning process in order to throughly clean the case. Fortunately, replacement labels are available.
After cleaning and reassembly the next step was to test the Power Supply. I found these helpful troubleshooting steps on the Forums. The Power Supply voltages check out but I was not able to get signs of life from the board. Based on the markings on the board, this is not a "Universal PET" logic board, it appears to be an earlier design. I was not able to find a schematic for this machine. Because of my own lack of familiarity with the PET and not being able to find the Schematic I have put further troubleshooting of this logic board on hold. I'm keeping the board here, and I hope to come back to it at some point.
In the meantime, I learned about a replacement Motherboard, The Future was 8 Bit 40/80D for the PET from the 8-Bit Guys's video on the topic. I was hesitant to purchase such an expensive part, but there were a couple of factors that helped push me in that direction. First, the PET is a very large computer. I will only be able to have one in the collection and it's hard to pick between the 40 and 80 column versions of the machine (which have some pretty significant software incompatiabilities). The 40/80D is DIP switch configurable, so you don't have to decide, it's two computers in one. I also knew that I would not have room for the massive external floppy disk drives, I prefer having a way to load disk images from solid state media. The SD2PET is a great option for that, but would cost over $100 delivered in the US, so between getting a known good replacement logic board, DIP switch changes between 40 and 80 column mode and the SD2PET built in, I decided to bite the bullet on this replacement logic board.
The 40/80D board fit quite well inside the PET case. It's about 1/3 of the size of the original board, but mounts at the back to the connectors fit out the back side. My Commodore PET 4016 didn't provide access to the User Port on the back or the second cassette interface on the side, but there were knock outs built into the case that I was able to remove in order to gain access to these critical areas. The UserPort is helpful because several PET games are available now that work with a Joystick Interface on the UserPort. The side panel where the second cassette used to enter is important because the SD card comes out there along with a couple of buttons, one for Reset and the other to bring up the DOS used for navigating the SD card. I ordered it from England and waited for it to arrive.
After in installing the 40/80 board, I was very pleased to find that the Monitor was working with zero repairs required! Of course, as with many of these project only a few minutes later I discovered that not a single one of the keys on the keyboard worked. I had already seen in an older 8-Bit guy video "Commodore PET Restoration" which shows exactly how to repair that, and the specialized metallic paint was in stock at Digi-Key. Of course while the keyboard was apart I cleaned all the keycaps. I temporarily lost one of the springs along the way, but was able to find replacements on eBay for only $10. Of course just a few days after the springs arrived and I had a fully functional keyboard again, I did find that lost spring.
So, with a cleaned and repaired Keyboard, working Monitor, replacement Motherboard, and a cleaned and re-labelled case, the Commodore PET 4016 looks better than it has in years...
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I've quite enjoyed poking around with the software provided by TFW8B, watching PET demos, playing Space Invaders and some other arcade classics and basically just looking at the machine. I don't have any nostalgia for this machine as we didn't have any Commodore at my school, but being the second version of one of the first home computers it's an iconic machine and I'm extremely happy to have one in the collection.
Do you have memories of the Commodore PET? If you are using a PET still, what are your favorite PET programs? Let me know in the comments below or feel free to shoot me an email. Thanks!
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