IBM 727, Руководство по инструкции

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14.0 SERVICE AIDS
14.1 FUSE REPLACEMENT
The fuses for the tape drive are located on the lower left, facing the rear of the
machine. The left row of fuses are for the AC lines; the right row are for DC lines.
Because a blown fuse leaves the tape drive in an unknown status, the tape drive door
should be opened before a blown fuse is replaced. An open tape drive door insures
that tape is not broken when the fuse is replaced, and it insures that some transient
condition does not cause writing on tape as the new fuse is inserted.
14. 2 ERASE HEAD POLARITY AND STOPPING DISTANCE
When in reset write status the erase head and the write heads should be mag­
netizing tape in the same direction. If the erase head were magnetizing tape oppo­
site to the write heads, then the write heads would reverse the tape magnetization
in seven tracks between record s. This reversal of tape magnetization is undesirable.
Determine the erase head polarity as follows:
1. Write a record of all one bits with either the control unit or the tape tester.
If using the tester, make sure the write triggers end up being off. (If not, keep
writing short records until they do end up being o f f .)
2. P ress the reset button on the tape drive.
3. Unload and develop the tape.
4. If the polarity of the erase head is correct, the marks on tape where the
write heads were turned off are very faint. See Figure 17a. If the polarity of the
erase head is wrong, the marks on tape where the write heads were turned off are
very distinct. See Figure 17b.
This same method can be used to check the stopping distance of the tape. How­
ever, if the marks under the write head are too faint to be seen, the following method
can be used to actually put bits on the tape.
1. Write the record of all 1 bits as before.
2. Pull the capstan motor plug and write a second record, ending with the write
triggers on. If using the tape control unit, it is necessary to disable the write trig­
ger reset line.
3. Reset the tape unit and unload.
A sim ilar procedure can be used for determining the stopping point after back­
spacing.
1. Write the record of all 1 bits.
2. Backspace.
3. Pull the capstan motor plug.
4. Remove the erase inverter to prevent the possibility of destroying the begin­
ning of the first record.
5. Write the second record, ending with the write triggers on (reset write tgr.
line disabled).
6. Reset the tape unit and unload.
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