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oscilloscope w ith two channels. TP3 is used in grounding the oscilloscope.
TP1 and TP2 are used in checking the read/w rite head for its different characteristics or in checking
and adjusting the tracking alignment, and the index burst timing.
(2) TP4 (read data
Signal)
This is the test point of the read data pulse. The READ DATA Signal appears here.
In FM mode, a data Signal with 2F or 1F period is observed, while in MFM mode, a data Signal with
2F, 1.5F or 1F period is observed. (See Table 106.)
This test point is used in check of asymmetry.
Mode
F re q u e n c y " " \ ^ ^
1 MB
1.6 MB
2F
4
/
a s
2 /
a s
1.5F
6 /
a s
3 /xs
1 F
8 /
a s
4
/
a s
Table 106
(3) TP5 (index sensor)
This is the test point of the index sensor photo-transistor output. A waveform with soft leading and
trailing edges appears here, since the sensor output Signal is taken out before flow ing across the
Schmitt inverter. Here it is necessary to check that the output voltage of the index sensor is normal
(with no waveform split).
(4) TP6 (write protect sensor)
This is the test point of the w rite protect sensor photo-transistor output. The WRITE PROTECT output
Signal appears here. W ith a disk in which a measure for w rite protection is taken (its notches are
masked), it becomes low level.
The voltage at this test point should be more than 3 V in the w rite enable state (the notches are open)
and less than 0.5 V in the write protect state.
This test point is used in check of the write protect sensor.
(5) TP7 (Disk-in sensor)
This is the test point of the disk-in sensor photo-transistor output.
This
Signal becom es low level w hen
a
disk is inserted into the
FDD.
(6) TP8 (track 00 sensor)
This is the test point of the track 00 sensor photo-transistor output. The voltage at this test point should
be within the ränge shown in Fig. 107.
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