TM
11-5835-243-34/EE641-AA-MMl-010/E154
MTT/TO
31S3-4-110-1
displaced signal. Measure the period from start of
(6) Measure record period over which initial
sweep to the center of time jittered initial signal
signal transition is time jittered (fig. 3-6, dynamic
transition (fig. 3-6) for 10 seconds minimum, at the
skew). Verify that the dynamic skew does not ex-
end of tape, center of tap, and beginning of tape
ceed 7.5 microseconds.
Record the maximum period. Verify that reverse
NOTE
static skew is 0.0 6.0 microseconds.
Do not allow tape transport to go into
e. Forward/Reverse Skew Comparison. Deter-
rewind status.
mine algebraic sum of forward and reverse static
(7) When EOT status is indicated, depress
skew measurements taken in tests in para c and d
STOP switch on exerciser. Observe that PARITY
above. Verify that total static skew does not exceed
ERRORS counter displays zero error.
0.0 4.0 microseconds.
d. Reverse Skew.
(1) Depress RUN REVERSE switch on
3-20. Tape Transport Troubleshooting
exerciser. Observe the two channels displayed on
When a tape transport fails any of the functional
oscilloscope and select either CH1 or CH2
troubleshooting tests in paragraphs 3-9 through
TRIGGER that allows the positive-going edge of
both signals to be displayed.
been completed, perform entire test to verify the
NOTE
repair.
The skew measurement to be recorded in
step (2) is used in para e below. If sweep is
CAUTION
triggered by CH1, the measured period is
When troubleshooting the tape transport,
assigned a positive (+) value. If triggered
observe all safety precautions. Discon-
by CH2, measured period is assigned a
nect electrical power unless performing
negative (-) value.
service required electromechanical or
(2) Observe time displacement of the most
electronic actuation.
Table 3-2. Tape Transport Troubleshooting Chart
Probable cause
Action
Trouble
SELECTED status light on exerciser
Unit not selected.
Check SELECT switch. select line must
be low.
off.
Replace A4 assembly.
Control logic bad.
Install cartridge.
READY status light on exerciser off.
Cartridge not installed.
Check SELECT switch. Select line must
Unit not selected.
be low.
Replace switch.
Cartridge in place, interlock switch
bad.
Access door not closed.
Close and lock access door.
Replace switch.
Door closed, interlock switch bad.
Wait to complete rewind.
Unit is rewinding.
Replace A4 assembly.
Control logic bad.
Install cartridge.
REWIND status light when
RWND
Cartridge not installed.
Position tape away from BOT.
Tape in cartridge is at BOT.
switch inside door is pushed.
Replace switch.
RWND switch bad.
Replace A4 assembly.
Control logic bad.
Install cartridge.
REWIND status light off when commended
Cartridge not installed.
Position tape away from BOT.
Tape in cartridge is at BOT.
to rewind.
Close and lock access door.
Access door not closed.
Command unit to stop.
Unit is in run command.
Install new tape in cartridge.
B O T status light off after complete re-
No BOT strip.
Installed new sensor and LED.
wind when commanded to stop.
Strip sensor or LED bad.
Replace A5 assembly.
BOT status light off after complete
Servo control bad.
Replace A4 assembly.
rewind.
Control logic bad.
Install new tape in cartridge.
EOT status light on exerciser off when
No EOT strip.
Install new sensor and LED.
at EOT.
Low tape sensor or LED bad.
Strip sensor or LED bad.
Replace A5 assembly.
Servo control bad.
Replace A4 assembly.
Control logic bad.
Clean commutator or replace brushes.
Unit goes into rewind status before given
Servo motor has noisy brushes.
rewind command and before EOT is
Install new tape in cartridge.
reached.
Cartridge has worn tape.
3-12
