Head Wear Service Check For Level 2 Attachments - IBM System/34 Maintenance Manual

25-998 Head Wear Service Check for
Level 2 Attachments
Head wear is determined by the head resolution and the
errors indicated on the inner tracks area of a diskette
(cylinders hexadecimal 40 through 4C).
Head resolution is the ratio of the signal amplitude of
hexadecimal FF in centimeters to the signal amplitude of
hexadecimal AA in centimeters multiplied by 100.
If the head resolution of both heads is more than 50,
the heads are good. If the head resolution of either
head is less than 40, that head is bad and the assembly
should be exchanged. When the resolution is between
40 and 50, use the ERAP data and the TU printouts to
determine if the head is bad.
The head is bad if the ERAP data and the TU printouts
indicate data errors on cylinders hexadecimal 40 through
4C on diskette 20 diskettes and the head resolution is
less than 50.
64
Example: Perform the following to scope head
resolution:
1.
Initialize a diskette 20.
a. Perform an IPL under SSP.
b. Sign on the system (if the system has the
password security function specified in the
machine configuration, you will need aid from
the customer to sign on).
c. Initialize a diskette 20 with the following
command:
INITfi"FORMAT
2. Set up an oscilloscope as follows:
Note: Use a Tektronix 453, 454, or a similar
oscilloscope with Xl0 probes.
Channel A sweep mode Normal
Channel A level
+
Channel A coupling
OC
Channel A slope +
Channel A source
External
Trigger
Normal
Mode
Add
Channell volts/division 5 mV/cm
Channel 2 volts/division
5 mV/cm
Channell input AC
Channel 2 input
AC
Invert
Pull out
Times per division
20 JJ.s/cm
Channel 1 probe
l
THP-13 (preamp TP1)
Channel 2 probe
l
THP-14 (preamp TP2)
Connect trigger to
A-A 1
Q2U~2
(+MS address compare)
1
See paragraph 25-950 for control card test pins.
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