IBM 727 Manual Of Instruction page 84

switch while the tape is in motion.
changed in a go status.)
19.4. 3 Measurement of Skew
A master tape (P/N 503928) for checking skew of the read-write head is provided
for every installation,,
Use the master tape and set up the tester and tape drive for reading.
tive timing between the 1 track and C track can be observed in the following manner.
Set the vertical calibration for ten volts per major division and the horizontal
calibration for 5 usee per major division.
use the read bus hub as the input.
track (the sync pulse), the trace can be shifted so that the peak lines up with the
center vertical line. Then set the response select switch to the C track, and ob­
serve the time position of the two signals. If it happens that the C track is leading
the 1 track, the sync and signal probes will have to be reversed.
six-usec skew (flutter) between 1 and C tracks is within specifications (section 1 5.2.6).
1 9.4 .4 Checking Forw ard-Reverse Magnet Transfer
The tape unit is loaded, selected, and read}\ The tester switches are set as fo l­
lows: read-write switch on READ, manual switch in neutral, the go-fb switch on
forward-backward, and the start-stop switch on. Alternately, the forward and r e ­
verse magnets are energized at a frequency determined by the start-stop frequency
dial.
The scope is set to a vertical calibration of 20 volts per division and a horizontal
sweep of four ms per major division.
be seen with the scope input at lp and a positive external sync from the go-fb hub.
For the reverse-m agnet wave form , the input signal is taken from In with the posi­
tive external sync from the go-fb hub (Figure 26).
19.4.5 Checking Moving Coil Wave Form
The tester set-up is the same as for checking forw ard-reverse magnet transfer
except that the go-fb switch is set to GO.
down. The scope is set for . 5 volts per division and five ms per major division.
The scope is not grounded as the input is taken from across edge connectors l r and
2n. CAUTION: The scope is about 100 volts above ground. Use an external sync
from the go-fb hub and change polarity to get a start pulse and a stop pulse (Figure 27).
(Damaged tape may result when tape motion is
This test can be made using the tape drive tester.
Sync the scope on the skew sync hub and
By setting the response select switch to the 1
The forward-magnet transfer wave form can
The moving coil now oscillates up and
84
The rela­
A maximum of