Over on [Ken Shirriff]’s blog is a tricky Commodore PET repair: tracking down 6 1/2 bad chips. WARNING: contains 8-bit assembly code.
The Trinity of 1977 which started the personal computer revolution were the Apple II, the Commodore PET, and the TRS-80. In this project it’s a failing Commodore PET which is being restored.
In the video below the break you can see [Ken Shirriff] and [CuriousMarc] team up to crack this tough nut. Resolving the various issues required a whole heap of software and equipment. Most notably a Keysight DSOX3104T oscilloscope, a Retro Chip Tester Pro, an old Agilent 1670G logic analyzer (this thing is rocking a 3.5″ floppy disk drive!), an old Agilent 54622A oscilloscope (also rocking a floppy drive!), a Data I/O 29B Universal Programmer With UniPak 2 insert, and the disassembly software Ghidra.
In the end there were 6 (and a half) bad chips which needed to be discovered and then replaced. This project is a reminder that it’s nice to have the right tools for the job!
If you’re interested in the Commodore PET you might like to read A Tricky Commodore PET Repair And A Lesson About Assumptions or Tracking Satellites With A Commodore PET.
If it’s an agilent (and with a colour screen, no less), it’s not old! HP with a green CRT the colour of my lawn, maybe…
That’s something I also like to think, but then I look at the calendar, and remember how long colour LCDs are actually around, and realize that I’m the one who’s old.
Interesting. That PET computer looks like a copy of an Sharp MZ-80K.. ;)
The PET came out before the Sharp MZ-80K though.
Man, the keyboard on the PET looks awkward to use.
I have always wondered about that keyboard. However did they come up with that, in a time where every device with a keyboard already had staggered keys: typewriters, teletypes, terminals?
They are just keys, like any on a staggered keyboard. It would hardly differ in price to stagger them instead of putting them in a grid like they did.
What is the story behind it?
They did fix it in the next version (PET 2001). However, to be honest, Commodore never really did have the best keyboards in their computers. I never touched a PET keyboard, but the keys look like those of the VIC-20 and C64, and those keys were muck. Usable but just sucky. Even the Amiga 500 keyboard sucked in a similar way, only with the Amiga 2000 did they start to use better keys. The Amiga 2000 was basically a German design, maybe that had something to do with the improvements in the keyboard area ;).
Why did Commodore give such a low priority to the quality of their keyboards? It’s the contact point between the user and the computer, and I’d think that you’d want to make that as pleasurable as you possibly can.
I found this story:
https://retrocomputing.stackexchange.com/questions/24471/why-didnt-the-original-commodore-pet-computer-use-a-standard-typewriter-style-k#:~:text=Such%20is%20relayed%20by%20Chuck,nicely%20crafted%20%2D%20out%20of%20wood.
I don’t buy Chuck Peddle’s argument. He couldn’t fit a staggered keyboard in that space???
Look at the models:
https://www.reddit.com/r/vintagecomputing/comments/ticirv/one_of_each_commodore_pet/
The problem clearly was the cassette tape. The PET 2001-9 is much wider than the PET 2001-32N, which meant a lot of more sheet metal, which is expensive. It doesn’t make sense to make a more expensive case to fit a cassette tape in, and then skimp on the keyboard because of cost consideration.
I think there was a fight between the design team and the engineering team, and Tramiel cut the wrong knot (i.e. let the design team win). Probably because indeed he thought it would be cheapest to reuse their calculator keyboards, and he just wanted the fight to be over. I think that’s how Jack thought.
I also think that it was an unfortunate decision that cost them a lot. Of the first 3 computer designs, I think that Tandy had it nailed down. Commodore must have seen that, as they basically copied the TRS-80 model 1’s design with the VIC-20 later.
The commodore keyboard of the first generation PET was awkward no doubt. But the keyboards that followed weren’t that bad, but it’s a matter of perspective. When you compared them to an old style mechanical typewriter everything was a step forward. But you forget one thing and that is cost, the home computer business was a killing market back in the 80’s 90’s and the cost of a keyboard could increase the total costs of a home computer significantly.
It’s therefore no surprise that some even went further and used rubber keys, but that’s not Commodore though (please ignore the “keyboard” for the Commodore MAX machine, now that’s the worse kind of keyboard you could get, fortunately not much of these machines were made. But we must keep in mind that they were never really intended for serious typing, mainly to add you name in a high-score list).
The keyboard was a pain, but I could touch type on it with practice.
The keyboards with the early Amiga 500 revisions (where, rather than 2 Amiga keys, there was a Commodore AND Amiga key) were actually quite nice. I had one of these! Unfortunately, it also had the Kickstart 1.2 ROM, that couldn’t boot from the hard drive (that came with Kickstart 1.3).
Later revisions of the Amiga 500 had more mushy keyboards.
https://www.amigaclub.be/knowledgebase/hardware/34/amiga-keyboard-types provides an overview of which models had which keyboards.
I have a Commodore CDTV, and it has a quite decent keyboard. A500 keyboard had a membrane and springs. But the A2000’s (and later “big box” Amiga’s) keyboard had a membrane and rubber domes. The springs were lineair, but the domes actually gave quite nice feedback.
But still not as nice as real professional keyboard switches like the Cherry’s. Somewhere halfway the 90’s, I was able to buy a Cherry PS/2 keyboard for a really nice price (for Dutch people: at the HCC Dagen ;)). And I’m still using it today. Also found out that it could switch between XT and PS/2 mode, and I was able to add a switch.
None of my Commodore keyboards ever came even close to that.
My first computer was a Nascom 1 (also from 1977). And believe it or not: its keyboard came with Licon magnetic-transformer keys. That was one of the nicest keyboards I have ever used in my life.
Nowadays I use a Microsoft Sculpt Ergonomic keyboard, and to be honest: it’s a solid third place, even though I find the overall construction quality of the keyboard low. I would use my Cherry keyboard every day, if I didn’t have RSI and needed the ergonomic keyboard. :)
I read Joshua’s comment as sarcasm. But I had a MZ80K and I thought the same even though I know very well that the PET came out several years earlier ;)
An article from April 2025? Have I been caught in a time machine or what??
The 1200 had a decent keyboard too.