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  • Writer's picturerehsd

Trying to Repair Some Commodore Computers!

Updated: Oct 9, 2022

I thought it would be interesting to see if I could repair some Commodore computers. I picked up four VIC-20 and two C64 computers that were sold for parts or repair. I also picked up a working C64 and C64C. I will post my progress on this page. I'm not sure how this is going to go! :)

My First Repair... a VIC-20

The first computer I am working on is a VIC-20. When I first turned it on, the video output looked pretty bad. It wasn't even fully readable and it was flashing in and out. After a replacement capacitor (C57) and some tuning of the trimpots (R7, R32) for the video, everything (except the keyboard, lol) is looking pretty good. I will fix up the keyboard later. I also plan to thoroughly clean the system, as it's pretty dirty. I may also replace all of the electrolytic capacitors. I need to research other common failures in these systems and see what suggestions are out there for other recommended fixes, part replacements, and recommended maintenance.

Board Assembly: 324003

Board Label: R-7HB

Board S/N: D-094473

Case S/N: 716908

VIC-20 #2

A quick fuse replacement and adjustment of a trimpot, and VIC-20 #2 is looking great!

Board Assembly: 324003

Board Label: KU-14194HN

Board S/N: F65806

Case S/N: 298654

VIC-20 #3

Had a key stuck down. After disassembling the keyboard and cleaning contacts with isopropyl alcohol, the keyboard is working well. This, along with a quick trimpot adjustment, has the system working well.

Board Assembly: 324003

Board Label: W-18 94HB

Board S/N: F187671

Case S/N: 1691070

VIC-20 #4

This unit has a bad VIC-I chip. After reseating the ROMs and bringing in a VIC chip from another system, everything tests fine. Now, I need to track down a replacement VIC-I chip.

Board Assembly: 324003

Board Label: W-18 94HB

Board S/N: 496618

Case S/N: 729461

C64 #1

After some troubleshooting, I believe this system has a bad PLA. I have parts on order to build a bunch of Daniël Mantione's PLA20V8s. After I get a good PLA in place, I'll see what other issues I find.

Update: The system is up and running. It had a bad PLA and bad RAM. The kernal ROM is a bit flaky, so I will need to track down some ROMs. The keyboard needed some love, too.

C64 #2

Same issue as C64 #1 -- a bad PLA (to start).

Update: The system is up and running. It did have a bad PLA.

In addition to what's pictured above, I added heat sinks to the ROMs, processor, and SID.

For both C64 #1 and #2, I built PLA20V8s. Here's one my test board:

C64 #3

Purchased as a working unit.


Purchased as working unit.

More to come...

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