IBM 727, Manual Of Instruction, Page: 47 / 163

14,3 MOVING COIL CIRCUITRY
For satisfactory operation, the moving coil must be excited by 50ma. Refer to
section 1 5 .8 .8 .
Marginal conditions in the moving coil circuitry can be determined by bias check­
ing the 140v supply to its lower limit. These conditions show up as increase in start-
stop time, i . e . , decrease in record gap. Prim arily, the tubes in question are T01J-4,
T01J-5 and T02J-4, T02J-5.
14.4 CHECKING FOR REVERSAL FAILURES
Trouble encountered while running program s involving backspacing, even though
the tape drive is in correct adjustment, may be due to reversal failures. A check for
reversal failures can be made as follows:
1. Write all 1 bits continuously on the tape.
2. Run a tape diagnostic that involves backspacing.
3. If the tape drive gives an error and continues to run forward when the program
is stopped, it indicates a reversal failure.
The tape drive can be stopped manually. The reversing circuits and mechanism
should be thoroughly investigated.
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