04
Aug
13

Aligning a Canon MD 5501 5.25″ FDD

Floppy drive minus shield

Floppy drive minus shield

A couple of weeks ago I mechanically serviced an old Canon 5.25″ floppy disk drive that came out of our old computer. As I mentioned here, the drive was in desperate need of repair and restoration. I decided to repair this particular drive mostly for sentimental reasons as it was the first floppy disk drive I used and learned programming with.

Firstly I had to make sure I had everything I’d need to make sure the drive was completely functional. It’s important to have some blank disks so you can test your new drives alignment without risking something with data on it. Another working floppy drive is a must as you’ll need to check that disks work in both drives correctly. Finally some software that tells you what track is under the head and how good the signal is. I found David Dunfields ImageDisk is perfect for that task as it gives a beep to tell you how good the signal is. This means you can hear the signal change as you manually move and adjust the head.

I ran the software with a good drive and a newly formatted good 1.2M disk, just so I could get a baseline and an idea of what I should get when the drive is repaired. Next I transferred the drive to be repaired into the machine so I could see what the current situation is. I used to software to move the heads back and forth to check that the mechanism was indeed completely functional with good results. The drive was however out of alignment as it was reading track 2 instead of track 0 where it thought it should be.

Every floppy disk drive has it’s own different mechanism for aligning the disks. Some of the older drives have a screw that you can adjust, others will be different. The Canon drive that I have is a one quarter sized drive, so it doesn’t have room for the older style of mechanism. In fact the stepper motor arrangement is pretty much the same as those of the newer 3.5″ floppy drives. My drive has two main ways of aligning the heads. It has a zero track sensor that can be moved after loosening a screw. It is basically and optical interrupter type sensor and is easy to adjust. The other way is to loosen some screws and move the whole head assembly. Fortunately I didn’t have to do that.

I remembered what my Dad had done to the drive. My Dad knows a bit about electronics and likes to fix things, and he did this a lot when I was a kid. I used to watch him work, and it’s part of the reason I like to fix things myself. Unfortunately Dad doesn’t know a whole bunch about fixing computer/digital electronics, including this floppy drive.

Dad was cleaning the old computer to get all the dust out. He took the drive out and cleaned the heads using metho like you do for tape recorders (which was the dominant audio medium of the time). In order to do this he had removed the upper head from the assembly to get better access. When he reassembled the drive he didn’t align the upper head with the lower one, and I found upon inspecting it they were a couple of millimetres out. Fortunately it was easy to fix, loosening a few screws, moving the heads and tightening. Appart from that he had actually done a pretty good job of cleaning it.

I finished aligning the drive by moving the optical sensor until I got the best result I could. But even though the drive was aligned it seemed to still find bad sectors randomly around the drive. I tried re-aligning it a few times to see if I could improve the situtation but couldn’t improve it. I found a few problems including the cable for the heads hitting the drives shielding. Still I couldn’t stop what seemed like random bad sectors. Each time I re-formatted the drive from scratch the bad sectors turned up in different places.

So it looked like there might be a problem with the heads themselves. I cleaned them with some metho and cotton buds much the same way as Dad did, but without removing the upper head. This seemed to yield better results, but not perfect. The heads in this drive are connected to the main controller board via some small cards in edge connectors on the board. I pulled these out and cleaned them carefully with medical wipes (they have isopropyl alcohol in them). This seemed to do the trick, floppies formatted and checked out with no bad sectors!

Finally to test the drive works with disks from other drives, I used the other drive to check the disks made by the one under repair and vice versa. They both were able to read and write to the same disks, and even both found the same bad sector on the main disk I had been using for testing. This is why I bought some “new” blanks, I was sure with all the fiddling I might damage a disk, turns out I was right to do so. The repair went so well, I’ve permanently installed the drive in my MS-DOS machine.

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