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3.
RDX, RDY, and -WEDGE
Use the oscilloscope differential input and connect the probes to pins
6 and 7 of U2.
This is RDX and RDY, the analog signal from a read
head, amplified by the flex circuit.
Expect about 20 mV p-p at the
disk outer diameter, 15 mV at the inner diameter.
This signal is
difficult or impossible to sync, and shows a broad band on the screen.
Now, trigger the oscilloscope on -WEDGE, pin 12 of U13, or pin 5 of
J5.
The servo bursts can now be observed, but all wedges are on top
of one another.
To separate them and observe the details of just one
wedge, trigger on pin 5 of U13, and delay the sweep.
Note that -WEDGE requires that the pulse detector and FYLO be working.
4.
+RAW DATA
Use another oscilloscope channel, and simultaneously with RDX and RDY,
observe +RAW DATA, the input signal to FYLO, on pin 6 of U9.
Observe
a TTL-type pulse for each transition of RDX and RDY.
5.
+ENCODED DATA
Observe at pin 4 of U9, or pin 13 of J5.
+ENCODED DATA is the output
of FYLO, and is the same as +RAW DATA.
6.
+READ DATA
Observe this at the same time as RDX and RDY.
It is a TTL-type sig-
nal, the input to DICEY, ready to be decoded.
It is synchronous to RD
CLOCK, and its presence means the servo is keeping the head on track,
and that the pulse detector and FYLO are operating.
7.
AMC Circuit
Observe BURST PEAK, pin 1 of U10, or pin 2 of J5.
Trigger using the
signal -WEDGE.
Look for a series of pulses (each about 10 micro-
seconds in duration) going negative from a 3.7 V dc base line.
The
pulse amplitude (from the 3.7 V dc base line) is proportional to the
amplitude of the servo bursts, and the group occurs simultaneously
with -WEDGE.
FYLO must be working to observe this.
5.5.3 Test Connector J5 Signals
Test connector J5 is used in the factory to test the PCB, but it also
provides a convenient place to observe some signals for trouble-
shooting.
The signals are listed in Table 5-1.
5-4
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