Align a Commodore 1541 disk drive

This year I set out to put together a working C-64 setup. And it worked great for about a week. Then when I started trying to load a few disks I hadn’t touched since sometime in 1992, my disk drives started protesting. I went from having two working 1541 disk drives to zero, thanks to alignment issues. Here’s how to align a Commodore 1541 disk drive.

Aligning a Commodore 1541 requires an alignment program, an unprotected commercially produced disk that works (Commodore’s Test/Demo disk is ideal), a screw driver, some thread locker, and a Commodore 64. It helps to have moderate mechanical ability and better than average patience. The 1541 was notorious for disk alignment issues, but it’s possible to fix them.

First things first: Does your 1541 disk drive need alignment?

Commodore 1541 disk drive
The type of Commodore 1541 on the right rarely goes out of alignment. If you have the style on the right and it won’t read disks, it’s probably dirty or oxidized.

Disk alignment is very easy to misdiagnose. If your drive doesn’t read disks at all, it’s more likely that it’s dirty or has an oxidized drive head than an alignment issue. Later 1541 drives with the Newtronics mechanism–the ones with the lever that turns instead of a drop-down door–rarely go out of alignment but frequently develop oxidized heads.

Alignment more frequently means the drive works intermittently. The drives I’ve observed will load a disk directory most of the time, but might not read the whole directory. When I load a program, the program might load one day and not load the next. Or the program might partially load, then the drive gives me an error near the end.

A drive that’s severely out of alignment can fail to read disks entirely, but alignment problems develop gradually as the shaft in the drive’s stepper motor slips, so it’s more likely to behave inconsistently.

Commodore 1541 alignment software

The best alignment software for the 1541 is a program from Free Spirit Software called The 1541/71 Drive Alignment System. There are others as well, but this one gives good feedback. These programs command the drive to read specific parts of the disk, then interpret the results to see and report what the drive actually did.

You can get an image of the 1541/71 Drive Alignment System, or a similar program, wherever you download other Commodore images. Every Commodore software archive I know about has at least one.

A misaligned drive may read track 17 or 19 when it’s supposed to read track 18. If it’s off by a track, programs fail to load, so you get lots of errors. The trick is to use alignment software to adjust the drive.

Disassembling the 1541

To disassemble a Commodore 1541 disk drive to align it, shut down the drive. Flip the drive over and remove the four screws on the bottom. Carefully flip the drive back over and remove the top cover. If the top won’t come off, it’s because you have the data cables plugged in. Unplug the cables, then the top comes off.

Then remove two screws on the side that hold the metal shield over the top. Remove the 3-pin connector that controls the drive light. Then remove the six screws that hold the lower part of the case to the rest of the drive.

At this point I like to put the shield back on and put the two screws in place. This allows me to work on the drive upside down, instead of on its side. I find it easier to work on it upside down.

On the underside of the drive, there’s a large stepper motor with two screws holding it in place. Loosen the two screws, but don’t remove them. Commodore secured them with enamel at the factory, so they can be tough. Try different sizes of screwdriver until one works. You should be able to turn the screws with moderate force. If you feel the driver slipping, you have the wrong size or your screwdriver is too worn out. If you strip the screws, you’ll make matters much worse. I found a new #2 screwdriver worked well.

While I have the drive flipped over, I like to tape a piece of paper over the transformer that protrudes out the back. This is where the high voltage comes into the drive. I’m more comfortable if I have something between the voltage and me while I’m working on the drive.

Aligning a Commodore 1541 disk drive

Commodore 1541 drive alignment
Aligning a Commodore 1541 disk drive requires more patience than anything, if you have the right software.

With the drive mostly disassembled and laying on its side or back, reconnect it to your C-64 or 128. Load your alignment program off a drive that works, or better yet, off a modern solid state solution like an SD2IEC, 1541 Ultimate, or Pi1541. These solutions can load your software without you having to find a way to write it to an actual Commodore drive, which is much more convenient and much more reliable.

Run the program, then when it asks you what drive number to align, enter the drive number. My Pi1541 and my real 1541 are both drive 8, so I loaded the program, shut down my Pi1541, then powered on my real 1541.

Insert a commercially produced, unprotected disk like Commodore’s Test/Demo disk that shipped with the 1541, then let the program continue. Use the left arrow key (in the upper left of the keyboard) and up arrow key (near the return key) to step the drives tracks up and down. You want to check the drive’s alignment at tracks 1, 18, and 35. If the drive can’t read track 18, it can’t load software. But it’s also possible for a drive to be able to read the high tracks reliably but not the lower tracks, or the other way around. You want to be able to read all three tracks with a reported condition of SATISFACTORY for the drive to be reliable. Don’t aim for perfection. Even emulated drives don’t give a reading of EXCELLENT on the critical tracks.

Adjusting the Commodore 1541 disk drive

After you loosen the two screws I circled in bright red, you align a Commodore 1541 disk drive by turning the big round motor a fraction of a degree.

If the drive’s condition reads POOR or NEEDS ALIGNMENT on one or more of those three critical tracks, you need to adjust the drive. Turn the stepper motor a tiny amount, and I do mean tiny. The motor’s full range of motion is only a couple of degrees. The software will tell you what track and sector it’s actually reading. Ideally, you should be getting readings from the software that you’re reading the target track (1, 18, or 35) and always see a number on the sector, because the software is aiming for the center of the track. A really badly misaligned drive will report it’s a track high, or at the half track. If the drive starts out at the half track and you adjust it and it reports it a track high, or low, turn the motor in the other direction.

It’s fiddly and requires a lot of trial and error. But within a few minutes, you should be able to get a reading of SATISFACTORY on all three tracks. Feel free to step through the whole drive and check the intermediate tracks, but if you can read all three, you should be able to read the others.

The software will also check half tracks. On early 1541 drives at least, you’ll usually get a reading of POOR on the half tracks. As long as you can step all the way up and down the disk without getting NEEDS ALIGNMENT, you should be good.

At this point, tighten the screws on the stepper motor back down.

Re-assembling your Commodore 1541 disk drive

At this point, quit the software, then shut down your C-64 and your 1541. Unplug the drive from the power before you start disconnecting data cables. Squirt a bit of thread locker on the screws on the stepper motor to hold them in place, and let it dry for about 30 minutes.

Place the drive mechanics in the lower half of the case and replace the six screws. Remove the two screws holding the drive cage, and remove the cage. Plug the drive light back in, then replace the cage and the two screws. Replace the top cover, then carefully flip the whole drive over and replace the four screws holding it together.

And that’s it. That’s how you align a Commodore 1541 disk drive.

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One thought on “Align a Commodore 1541 disk drive

  • February 16, 2021 at 10:21 pm

    nice article. i may be going down this road soon, but first I delve into getting an image of the alignment software.

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