Upgrading the Commodore PET 2001-8: Part 1
I recently received the PET microSD with datasette power and Commodore PET 2001 ROM/RAM upgrade board from Tynemouth Software, so I thought I’d document the upgrade process for those interested in doing it themselves. I’ll be upgrading my Commodore PET 2001-8, last seen in a new article I wrote for PC Gamer. Although my main PET is a SuperPET, I’d love to get this more interesting vintage specimen up to snuff as well.
While I’m not going to address the rust spots or other case issues, I did first want to address a slight wobble my unit has. Perhaps it’s from a slightly warped metal case, because all four feet seem to be present and fairly level. My idea to fix it is to just to take another sticky foot pad thing and put it on the left front foot, which is the side that’s slightly elevated.
Since I wasn’t satisfied with the pad in the first photo because it was square when the foot itself was round, I did find a perfectly shaped circular pad in a baggie of miscellaneous ones I had.
With that minor issue resolved, I wanted to power up the PET again just to make sure everything was still functional.
As you can see, it works! The screen is crisp and gorgeous and every key on the keyboard works, although 2918 bytes free of memory doesn’t sound quite right. It should instead have 7167 bytes free. Hopefully the one upgrade fixes that RAM issue by bypassing it completely.
Before I get to the first upgrade, I just wanted to check if the tape drive worked. Last time I recall, it didn’t read in a tape. If it doesn’t work this time, I’ll wait on replacing that in the future (if I bother at all since I can just use one of a seemingly infinite number of external tape drives I have).
Unfortunately, no luck. It’s something I’ll have to test again with a different tape in the future, maybe doing a head cleaning and demagnetizing first, but I think the internal tape drive is probably shot.
So, for the first upgrade, I’m going to have to open up my PET.
On mine, there are only two screws – one on each side – holding the case down.
With both screws removed, I lifted the lid up. Yes, it’s as terrifying as it looks.
I need to replace the CPU chip with this new board. The dip switch settings on the new board are set to 32K RAM (from a choice that also includes 8K and 16K) and BASIC 4 (from a choice that also includes PET tester, BASIC 1, and BASIC 2), so that’s good for me.
Now I just have to remove the CPU.
That chip was in there good, but I eventually got it out with a standard chip puller. One of the 6502’s pins got bent fairly badly in the extraction, but fortunately, I shouldn’t need it again and can always work on unbending if I ever did.
Now it’s time to insert the new board.
Another tight fit and a struggle, but it eventually went right in.
Now to close the lid and see what happens when I turn it on.
And… nothing but bars on the screen. It turns out I have to put the CPU in that socket on the new board. Doh! Now to carefully unbend that darn pin!
Still a little crooked, but hopefully it will go in.
And… the pin snapped off. So, off to eBay to get a replacement 6502 chip!
So, there will be an unexpected part two in a little more than a week, then.
Part 2 is now live.