Editing Floppy Drive Repair (section)

== Alignment and adjustment ==

{{Warning|'''Radial head alignment cannot be done by trial and error, and attempting it makes a drive worse far more often than it makes it better.''' It requires a certified alignment diskette — one that cannot be copied — and an oscilloscope. Tandon specifies the '''Dysan 224/2A''' or equivalent for its 48 TPI drives, and requires both diskette and drive to stabilise at room temperature for '''one hour''' before any check.<ref name="tandon" />}}

'''Rule out everything else first.''' Alignment is the diagnosis of last resort. True alignment drift is indicated when '''both''' of these are true:

# Disks formatted in the drive read back correctly '''in that same drive''', and
# The drive cannot read good disks formatted on a known-good, correctly aligned drive.<ref name="mzd" />

Even then, the more likely causes are:

* '''A dirty track 0 sensor.''' Chuck(G), quoted on minuszerodegrees, notes that many apparent alignment faults on these drives turn out to be a dirty track 0 sensor.<ref name="mzd" /> Clean the optics before touching anything adjustable.
* '''Rail drag''' — the carriage not reaching the commanded cylinder.
* '''Spindle speed out of tolerance.'''
* '''The media.''' A double-density disk written or formatted in a high-density 1.2 MB drive does not meet the double-density standard and often cannot be read in a DD drive.<ref name="mzd" />

=== Spindle speed ===

The one adjustment that is safe to make. Tandon's specification for the TM100 series is '''300 RPM ± 1.5 %''' — 295.5 to 304.5 RPM — adjusted at R4 on the servo board.<ref name="tandon" /><ref name="mzd" /> Most 300 RPM drives of the period share both the figure and the adjustment method. Three ways to measure:<ref name="mzd" />

# The '''strobe rings''' moulded or printed on the spindle flywheel, one marked 50 Hz and one 60 Hz. Use the ring matching your mains frequency, under strong mains-powered fluorescent light. The pattern should stand still.
# '''ImageDisk's Test RPM''' command, or an equivalent utility.
# A digital oscilloscope with a frequency readout on the tachometer output of the speed-control IC.

Check the spindle flywheel's securing screw is tight before adjusting anything — a loose one causes a speed error that no adjustment will fix.<ref name="mzd" />

=== Track 0 ===

Track 0 detection is an optical or mechanical switch plus a mechanical stop. Clean it first. Adjust it only per the drive's own service procedure — Tandon's is Sections 5.9 and 5.10, with a defined switch position and a separate stop adjustment.<ref name="tandon" />