Commodore PET Model CBM 3008


He we have a Commodore PET model CBM 3008 which dates from about 1979. The PETs were rebranded as CBM for the European markets. This one was listed on ebay as completely dead so i was able to acquire it fairly cheaply. From the outside it is in very good cosmetic condition.

There is a first look video here.







Inside is a different story! The main PCB is caked in dust and crud.




After an hour or so with isopropyl alcohol and a lot of cotton buds the board is looking much better. There are few integrated circuits with rusty pins but generally it's in good condition. While the PCB was out of the case i cleaned up the inside and checked the power supply, all the correct voltages appeared to be present.




With the main PCB refitted it's time for the big switch on..... Well no smoke, so that was good and there is a sort of picture on the monitor.







As it happened i had a friend visiting who worked in a TV repair shop many years ago when all TVs were CRTs and he said that the problem with the screen looked like a power supply issue with the monitor. The PET's monitor is a very simple device and just changing the 12V regulator in it's power supply got the picture back.




However as can be seen the PET is reporting the wrong amount of memory. The CBM 3008 would have had 8K of memory originally but the board had received a full up grade to 32k. So the reported memory should be '31743 BYTES FREE'. What it is actually reporting is '23235 BYTES FREE'.




This particular model of PET uses 4116 RAM chips, these are known to fail over time but fortunately are still available. Unfortunately they are soldered into the board. As it is possible that at some point in the future other RAM chips will fail i deceided to very carefully desolder all of the RAM chips and replace them with sockets. It turned out that only one chip was faulty and once that was replaced the PET reported the correct amount of RAM. All the ROMs for these computers are available for download on the internet so i decided to upgarde the basic ROMs to the latest version, Basic 4.0. I also had to replace the VIA chip (6522) which interfaces to the user port. This chip had quite badly rusted pins and while i was working on the RAM fault one of the pins fell off! Again these are still available.




Here it is finished on it's desk with the CBM 8050 Dual Floppy Disk Drive.

Here is a video of the PET in action after it's restoration. There are several other videos on my YouTube Channel showcasing various games for the PET.



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