TAPE TRACKING AND SKEW ADJUSTMENT AFTER PARTS REPLACEMEI\

Tape tracking and skew checks should be performed when any of the following components are replaced:

Upper Swing Arm tracking) and read/write head alignment (skew) procedures:

alignment of the capstan to the tape path assures that the tape

.. BIT 4 SYNC

BITS

-STATIC SKEW

t - - - t - -TURNAROUND JUMP

NO STATIC SKEW 1 - - - I TRACKING AND SKEW

PROPERL Y ALIGNED)

Figure '-1. Static and Dynamic Skew and Turnaround Jump 7.4.1 Capstan Alignment (Tape Tracking)

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The capstan motor is mounted with three spring-loaded screws.

Adjusting the screws will influence the lateral position of the capstan wheel. The capstan wheel must be positioned so that the tape travels properly in the tape guide, as in the following procedure:

1. Open the threading cover and remove the outer flange from the upper tape guide.

2. Close the threading cover, mount and load a known good scratch tape, then open the threading cover to provide access for checks and adjustments.

3. Enter rna i ntenance program 00 to move tape forward .. Ensure that tape is flush with but not forced against the rear flange of the upper guide and is not riding over the front of the upper guide. If necessary, adjust capstan motor mounting screw 3 .. Refer to Table 7-1 and Figure 7-2.

4. Enter maintenance program 02 to perform the shoeshine routine (forward/backward tape motion). Ensure that tape;s not pushed against the back flange or hanging over the front of the tape guide in either forward or backward motion.

Table 7-1. Capstan Alignment Instructions CONDITION

Tape tracks to front edge in both forward and backward Tape tracks to back edge in both forward and backward Tape tracks to back in forwar'd and tracks to front in backward Tape tracks to front in forward and tracks to back in backward

READIWRITE HEAD ALIGNMENT SCREW

AD JU·S TMENT Turn screw Turn screw Turn screw turn screw Turn screw turn screw

CAPSTAN WHEEL

READ/WRITE HEAD

3 CW 3 CCW

1 CW or 2 CCW 1 CCW or 2 CW

Figure 7-2. Capstan and Read/Write Head Alignment

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If necessary, use instructions in Table 7-1 and Figure 7-2 to adjust tracking so that the tape travels in the same position on the guide in both forward and backward directions.

Ignore at this as the capstan out the jump.

time any tape jump which may be present just changes direction; do not attempt to adjust 5. Check tape position on the capstan wheel. Ens'ure that tape tracks towards center of the capstan wheel and does not overhang the wheel on either side. If necessary, adjust motor mounting screw 3 as in step 3 above. If an adjustment was necessary, repeat step 4 above.

6. Unload and remove the scratch tape and reinstall the outer flange of the upper tape guide.

7.4.2 Head Skew Adjustment

The head skew must be adjusted so that all bits of a data byte will come under the R/W head within a specified time window. The adjustment also ensures that the head is not so skewed that it reads bits from more than one data byte at a time.

1. With power off, remove the card cage cover and disconnect the write head cable from the front of the WR card (slot A4).

2. With power on, mount and load a master alignment tape without a write enable ring. Tape must meet the requirements of Storage Technology specifications. Ensure the File Protect indicator is illuminated at the completion of the load.

3,

CAUTION

Never do a high speed rewind on a master alignment tape.

Connect a dual-trace oscilloscope channel 1 to bit on the RD card (slot A6) and channel 2 to bit 5

(Refer to Figure 7-3) The scope settings should follows:

4 (Tp 4) (Tp 5).

be as

Sweep microseconds. If necessary, readjust the read/write head

RD CARD (SLOT ASI

TP10 0 TP9 0 TP4 0 TPS 0 TPO 0 TP10 TP20 TP8 0 TP30 TP70 TP50 TP110

GROUND

veo ERROR VOL T AGE BIT 4

BIT S BIT 0 BIT1 BIT2 BIT P BIT 3 BIT 7 BIT 5 GROUND

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alignment screw. (It may be necessary to perform steps 10 and 11 three or four times to ensure that forward and backward skew are negligible.)

12. Enter maintenance program 02 to perform the shoeshine routine. Examine closely the upper tape guide and ensure that tape is not forced to the guide flanges. This can be best accomplished by removing the outer flange of the upper guide and ensuring that tape does not overhang the guide.

Reinstall the flange when the check is completed.

13. If necessary, very slightly adjust capstan motor mounting screw 3. If this adjustment is made, return to step 10

Failure to achieve proper alignment may require reperforming this procedure or may indicate a defective component in the tape path, such as bent swing arm, a defective capstan, or a burred or nicked tape guide or flange. A bent swing arm is often characterized by excessive tape jump on the capstan as

tape direction changes.

14. Measure the dynamic skew (timing jitter) using the following measurement technique:

a) Enter maintenance program 00 to move tape forward.

b) Sync scope on Bit 5 and measure the timing width of the scope trace at 0 Vac point (50% point of peak-to-peak transition) ,

c) sync scope on Bit 4 and measure the total time width (jitter) of Bit 5 scope trace at 0 Vac point,

d) The dynamic skew is equal to the measurement of Step c minus the measurement of Step b. It must be equal to or

less than 7.0 microseconds.

e) Enter maintenance program 01 to move tape backward and repeat Steps b through d to measure backward dynamic skew. It must be equal to or less than 7.0 microseconds.

15. If dynamic skew is not within specifications, check for defective tape path parts. If any parts must be replaced,

repeat entire tape tracking and skew adjustment procedure.

16. When the tracking and skew requirements are met, unload and remove the master alignment tape. With power off, reconnect the cable to the WR card and reinstall the card cage cover.

17. Run all internal diagnostics.