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Read Amplifier Calibration
Three potentiometers have been used in the read
amplifiers and bit detectors to facilitate setting
the regulated signal output and the bit detection
threshold. The following calibration procedure is
recommended:
1.
Deselect the heads by depressing GENERA
L
RESET on the Disk Synchronizer, and balance
the DC level appearing at pins Hand G of the
Overdriven and Limiter Amplifier (AMX-) to
within O. 1 volt of each other by means ofthe
potentiometer on the card.
2.
Set the machine to a continuous read condition
on the track and sector. Cylinders around
132 should be used because the amplitude
difference between single bit and all bit
patterns at that location will be slight.
3.
Use a 1-to-1 or a X10 compensated probe
with a wide band (2 mc or greater) preampli-
fier. Sync on index; use an expanded scale
of about 50 microseconds per cm, and observe
an AGC burst on pins A and F of the second
Linear Amplifier (ANF-) (Figure 2-3).
4.
Adjust the voltage level that appears at these
pins for a value offrom 6 v to 6.25 vby means
of the potentiometer on the AGC Detector
(A
UE-).
5.
If
this voltage level cannot be obtained, the
AGC Detector (AUE-), the Variable Gain
227-5583-1 (11-62)
Amplifier (ANE-), and the subsequent two
linear amplifiers (ANF-) should be checked.
NOTE:
On some machines, the card code for the
AGC Detector may be listed as ANH-j
A UE - is the later designation.
6.
Referring to Figure 2-4, observe the wave-
form that appears at pin A of the OR- AND
(ANW-) and by means of the potentiometer
on this card adjust the clipping level to 50%.
NOTE:
This is easily accomplished by maintaining
E2 (Figure 2-4) at a constant vertical de-
flection of one cm (by means of the oscil-
loscope variable voltage control), and by
adjusting the potentiometer on the OR- AND
(ANW-) to obtain a vertical oscilloscope
deflection of two cm for E 1 (Figure 2-4).
It
is very important that the base line of
reference used for measuring the clipping
level be after the recovery time as shown.
Any overshoot is to be disregarded in the
measurement of the 50% level.
DISK SURFACE REQUIREMENTS
The 353 disks are mechanically and electronically
perfect.
Servicing Procedures
2.3
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