Editing Sinclair QL Microdrive Troubleshooting Guide (section)

== Spinning a drive for test ==

To check a drive mechanically or with a scope you need it to run continuously. Sinclair's program does this — key it in with a known-good pre-recorded tape in MDV1:<ref name="sm" />

<pre>
100 DEFine PROCedure sedes(n,flag)
110 reg=98336:pc_sel=2+flag
120 FOR i=1 TO n
130 POKE reg,pc_sel
140 pc_sel=pc_sel&&253
150 POKE reg,pc_sel
160 pc_sel=2
170 END FOR i
180 END DEFine

200 DEFine PROCedure start_mdv(n)
210 sedes n,1
220 END DEFine

300 DEFine PROCedure stop_all
310 sedes 8,0
320 END DEFine
</pre>

<code>start_mdv(n)</code> turns on drive ''n'' and keeps it spinning; <code>stop_all</code> stops all drives.<ref name="sm" />

With a drive spinning:<ref name="sm" />

# Using an oscilloscope, check that a signal is present from the read head (INA at IC29) and trace it through to the RAW inputs on the ZX8302.
# '''Nothing from the head''' — the head is faulty (drive replacement).
# '''Input to IC29 but no output''' — faulty IC or headboard component.
# Check the headboard connector the same way.
# Repeat on the second drive. '''If both drives appear to work, suspect the ZX8302''' — it is socketed, so it is easy to substitute.
# Check the clock signal on pin 25 of the ZX8302.

A known-good ZX Microdrive plugged into the external Microdrive port is another way to decide whether the fault is in the machine or in the drives.<ref name="sm" />