HP 7970B Operating And Service Manual page 21

7970B/7970C
b. Using retaining ring pliers, remove outer retaining
ring holding tape roller to tension arm. (See figure 6·6.)
c. Note the positions of the shims and washers and
remove the shims, washers, and tape roller from tension arm
shaft.
d. Remove the tension arm spring.
e. Remove the three screws and washers that secure
the tension arm to the transport casting.
f. Mount the new tension arm assembly and reassem·
ble in reverse order of disassembly.
g. Perform adjustment procedures described in sec-
tion V.
4-18. PHOTOSENSE ASSEMBLY.
4-19. The photosense assembly (EOT/BOT) position rel-
ative to the tape path is critical. The following procedures
describe replacing the EOT/BOT photosense assembly.
a. Loosen (do not remove) the two screws that secure
the photosense assembly to the transport housing.
b. Remove the photosense assembly from the housing.
c. Note the color-coding of the wires attached to the
photosense assembly and remove the wires.
d. Strip and solder the wires to the new photosense
assembly in the same positions noted in step "c."
e. Inspect the photosense insulator remaining on the
transport. If the insulator is damaged, remove and replace
with a new insulator (HP part number 07970-01176).
f. Place the new photosense assembly into position
and tighten the screws just enough to allow the position of
the photosense assembly to be shifted.
g. 'Thread a reel of tape on the transport and position
the photosense assembly 1/8-inch from the tape. Ensure
that the face of the assembly is parallel to the tape path.
h. Tighten the photosense mounting screws.
4-20. MAGNETIC HEAD ASSEMBLY.
4-21. The magnetic head assembly contains all critical
tape path components. Use extreme care in handling the as-
sembly. The following procedures describe replacing the
magnetic head assembly.
a. Disconnect the magnetic head assembly connectors
from the read preamplifier assembly and write interconnect
assembly (units equipped with write data modules).
Part 2
Repair and Replacement
b. Remove the two screws that secure the read pre-
amplifier assembly to the transport casting.
c. Position the read preamplifier assembly to allow
access to the magnetic head assembly.
d. Remove the three hex-head screws that secure the
magnetic head assembly to the transport casting.
e. Carefully remove the magnetic head assembly.
CAUTION
The magnetic head assembly contains all critical
tape path elements. Do not allow the guides,
cleaner, or head assemblies to contact the trans-
port casting. Use extreme care in positioning the
magnetic head assembly as not to scratch the
head surface or misalign the tape path elements.
f. Carefully place the new head assembly into posi-
tion and secure it to the transport casting with mounting
hardware.
g. Replace the read preamplifier assembly and recon-
nect the magnetic head assembly connectors.
4-22. REEL SERVO PRINTED-CIRCUIT ASSEMBLY.
4-23. The reel servo printed-circuit assembly replacement
is not critical; however, the mounting bracket of the assem-
bly also serves as a heatsink. Prior to installing a new or re-
paired reel servo printed-circuit assembly, ensure that the
transport mounting surface and the assembly mounting sur-
face are well coated with a thermal-compound.
4-24. CAPSTAN SERVO PRINTED-CIRCUIT
ASSEMBLY.
4-25. The capstan servo printed-circuit assembly replace-
ment is not critical; however, the assembly contains a strap-
ping network in the form of a dummy DIP connector. The
position of this connector on the assembly is very critical.
If the unit is operated with the connector removed or in the
wrong position, damage to the unit may result. Refer to
figure 7-10, Capstan Servo Assembly Schematic Diagram to
determine correct position of the connector.
4-26. The mounting bracket of the capstan servo printed-
circuit assembly also serves as a heatsink. Prior to installing
a new or repaired capstan servo assembly, ensure that the
transport mounting surface and the assembly mounting sur-
face are well coated with a thermal compound.
4-3/4-4