Amiga Floppy Disk Drive Track Alignment

Summary

A floppy disk drive can get out of alignment for various reasons. This happens when the heads are not aligned with the tracks on a floppy disk compared to the Track 0 sensor.

A typical symptom of a misaligned drive is that it can format a floppy disk, that it can read and write, but cannot read (and subsequently, write) to an original unmodified disk, or one that was formatted on another well know good drive.

The re-alignment process makes micro adjustments until the Track 0 sensor is aligned with Track 0 on the floppy disk. The way to detect whether these are aligned is to use X-Copy CheckDisk feature, which reads the blocks on the tracks and reports back how good or bad the reading is. When the CheckDisk process reports everything is healthy then the re-alignment is successful.

Requirements

To re-align a floppy drive the following are required:

• An original known good working AmigaDOS floppy disk. Like an original Workbench disk. Or a disk formatted on a known good floppy drive.

• ATK (Amiga Test Kit) - download ADF images from https://github.com/keirf/Amiga-Stuff

• X-Copy 3 and above, with CheckDisk function - download ADF images from http://jope.fi/xcopy/

• Be able to boot in to X-Copy or ATK on floppy with a good drive, or as an ADF with a Gotek drive.

Drive Signal Tests

It is assumed, and required, that there is nothing else wrong with the floppy drive and that all other drive signals and functions are working.

To check and confirm this, boot in to Amiga Test Kit and use the Floppy Drive Signals Test to test the suspect floppy drive.

Check that:

1. You get a READY signal, when a floppy disk is inserted.

2. You can stop and start the motor.

3. You are getting index pulses when the motor is running.

4. You can step in and out of Track 0.

5. You can step in or out by changing the direction.

Track Alignment Methods

There are two ways to re-align a floppy drive depending on the type of the suspect floppy drive.

Most, if not all, drives will have an adjustable Track Motor to move the read/write heads, but not all drives will have an adjustable Track 0 sensor.

• Drives with adjustable the Track 0 sensor. There is typically a screw that holds the Track 0 daughter board in place, with glue to prevent the screw loosening. The Track 0 daughter board can usually be adjusted back and forth on slot holes.

• Drives with a non adjustable Track 0 sensor, but have adjustable Track Motor. There are typically two screws securing the Track Motor.

Depending on which type, depends on how you make the adjustments. Both methods makes use of using the X-Copy CheckDisk feature to determine how aligned the Track 0 sensor is with the tracks on the known good floppy disk.

X-Copy CheckDisk

The X-Copy CHECKDISK function will check all the selected tracks on the disk for errors. For tracks confirming to AmigaDOS, a green 0 (zero) is shown. For tracks not conforming to AmigaDOS, a red error number will be displayed. These numbers are as follows: -

1 - More or less than 11 sectors on the track,

2 - No sync found .

3 - No more sync found after gap.

4 - Header checksum error

5 - Error in the header / long format

6 - Data block checksum error.

7 - Long track.

8 - Verify error.

When you first run CheckDisk on an misaligned drive you will get red errors numbers - this screen shots shows red errors at the beginning of the CheckDisk whilst it is running:

The end goal of the re-alignment process is to get all green 0's (zeroes) as the final result of CheckDisk :

Re-alignment by adjusting the Track 0 Sensor

This example is for the Chinon FB-254 drive. Refer to the diagram above.

Boot up X-Copy and select the suspect drive as the Source, ensuring that it has its power and data cable connected properly.

Locate the screw securing the Track 0 Sensor daughter board. Locate the two alignment slots and remove any glue in it.

Put in the known good AmigaDOS floppy disk in the drive.

Follow the following steps to re-aligned the drive.

1. Start the X-Copy CheckDisk function.

2. Loosen the screw securing the Track 0 Sensor daughter board.

3. Micro adjust the Track 0 Sensor daughter board, along the alignment slot.

4. Let X-Copy CheckDisk read for a few blocks.

5. If you get red error numbers, go back to Step 3 and repeat, going in the opposite direction if you reach the end of the alignment slot and start X-Copy CheckDisk again if required.

6. If you get green 0's then got to proceed to next step.

7. Tighten the screw and let the X-Copy CheckDisk finish.

8. Repeat X-Copy CheckDisk again.

9. If you get red error numbers again then go back to Step 1.

10. If you all green 0's then alignment for that good known disk is complete.

It is advisable to perform the X-Copy CheckDisk on a variety of known good disks, as there may be very small variations in track alignment between floppy disks and drives that become edge cases.

Re-alignment by adjusting the Track Motor

To come...