Michael Wolf
Projects and thoughts from the best view in Cincinnati an okay view in San Jose a chill view of the interstates of Oakland
Home Projects Photos Github Mastodon Nullbrook RSS
Troubleshooting the Commodore 64: Solutions to Issues I Have Encountered
Last edited - 24/06/17

I imagine that I will be running into a lot of issues as I begin to tinker with the Commodore 64 so I'll use this page to keep track of some of the problems and solutions.

Fixing the Latch on the 1541-II

I had a very curious issue only about a week after setting up the Commodore system with my only operational disk drive. The drive simply would not latch down or read the disk. I got a dreaded drive read error every time I attempted to invoke LOAD. The drive screamed at me and flashed a red error light. This latch was just bouncing around when pulled down, clearly something was awry. At least the drive was turning on. Otherwise I would have imagined myself in much scarier territory.

Ain't it a beaut

The 1541-II operates based on a latch on the front face. When operating correctly, the latch gives some feedback as it is dropped from the starting horizontal angle down 90 degrees to the lock position. There is an audible click as drivehead comes down onto the disk. Unfortunately in my situation, the latch seemed to be totally disconnected. Before diving into the internals of the drive, I called my father to ask if he had ever run into a sitution similar. To my surprise it had happened to him alot and he told me the little metal piece I'd need to wiggle inside the 1541-II. So I did my favorite part of any electronic operation and removed the screws from the bottom of the drive before removing the cover.

Aha! Look at that. That's a pretty little system. Clearly I had to push it a bit. Yes the drive seemed just fine. I was still amazed at how mechanical the whole system was. Despite all of my years volunteering at the Cincinnati Computer Cooperative recycling facility, I had come to think of computer components as essentially black boxes.

Boop

After messing around with the internals and tracing the functions of the drive, I was able to spot where the latch was making its connection to the drivehead mount. Indeed, just as my father mentioned, there is a little metal rod between the latch connector and the carriage. In order to push the drivehead down, this rod needs to go over a slightly raised part of the carriage, pushing it down as the latch twists clockwise. This would explain the tension and how the rod get held in place when locked.

As my father had described, this rod had indeed slipped out of place so that the latch no longer had an effect on the drivehead carriage. A little push seemed to be all that would be needed to fix it.

Indeed it really was that simple. After making sure it would slip back out anytime soom, I sealed it up and brought the system back to life. I don't know why this design was chosen for the latch connector, but I'm glad the fix was easy. And I guess I should cut it some slack, it's still chugging along 30 years after manufacture. I don't imagine I'll be able to say the same about my PC's hard drives.

*drum roll*
Yeah! Dragon's Lair!
Syntax Error? Not on my Smart Term

I'm still figuring out how the LOAD command works so this one really stumped me. As I was loading up my Mighty Mo terminal disk, I went through my standard load-from-floppy-drive steps to the following result.

READY
>LOAD "*",8

SEARCHING FOR *
LOADING
READY.
>RUN

?SYNTAX ERROR IN 20295
READY.
>LIST

20295 COLRPHTMS64SPRITES

Okay well shoot, this disk is pretty old, maybe it's corrupted. I tried the other side.

READY
>LOAD "*",8

SEARCHING FOR *
LOADING
READY.
>RUN

?SYNTAX ERROR IN 8054

Uh oh, I'm not confident in my ability to fix this disk from the C64 and my setup for connecting from a PC has yet to be tested. Fear of trying to edit this program in BASIC made me shiver a little, but setting up the PC->C= link shouldn't be too bad. But maybe I can receive mana from the Internet to save a moment. And sure enough, a forum post that did not include a dead link to a geocities site suggested I try loading the program absolutely.

READY
>LOAD "*",8,1

Of course it worked. This program must be machine language. Thank you Internet.

Disk Read Errors

There is the horrible mechanical sound like a little plastic machine gun that occurs when the read head can't get a grip on the disk it's trying to parse before giving up and sending a signal back to the console. It turns out that scrubbing the brown residue off the read head with rubbing alcohol and a cotton swab helps dramatically. How did I even manage to read anything with the head so dirty? There are also disk cleaning disks or the DIY put-printer-paper-in-a-disk-and try to read it trick which didn't work in my experience for the more caked-on dirt.

To the top!