Editing Floppy Drive Repair (section)

=== 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" />