HP 7970B Operating And Service Manual page 20

Repair and Replacement
4-5. The following procedures are recommended when
component replacement is necessary.
a. Remove defective component from board.
b. If component was unsoldered, remove solder from
mounting holes with a suction device (table 4-1) or a wooden
toothpick.
c. Shape the leads of replacement component to
match mounting hole spacing.
d. Insert component leads into mounting holes and
position component as original was positioned. Do not force
leads into mounting holes; sharp lead ends may damage
plated-through conductor.
Note
Although not recommended when both sides of
the PCA are accessible, axial lead components
such as resistors and tubular capacitors can be
replaced without soldering. Clip ends of defec-
tive component near body. Straighten leads left
in board. Wrap leads of replacement component
one tum around original leads. Solder wrapped
connection and clip off excess leads.
4-6.
REPLACEMENT.
4-7. The 7970B/7970C is of modular design. All major
transport assemblies are easily accessible for repair or re-
placement. The following paragraphs describe replacement
of critical transport assemblies. Refer to section VI for de-
tailed views of mechanical assemblies.
4-8. TAPE ROLLER AND BEARING ASSEMBLY.
4-9. The tape rollers are precision referenced to a step
on the mounting shaft. The bearings are very critical to pre-
loading. When replacing the tape roller and bearing assem-
blies refer to section V for adjustment procedures to prop-
erly preload the bearings.
4-10. CAPSTAN (10 - 37 .5 IPS UNITS ONLY).
4-11. The capstan replacement requires that the capstan
motor assembly be removed from the transport. The posi-
tion of the capstan is referenced to the mounting surface of
the capstan motor assembly, The following procedures de-
scribe capstan replacement.
a. Disconnect capstan motor and tachometer connec-
tors from capstan servo printed-circuit assembly.
b. Remove four socket-head screws securing the cap-
stan motor assembly to the transport casting.
4-2
7970B/7970C
c. Loosen two socket-head set-screws holding the cap-
stan to the motor shaft and remove capstan.
d. Place the capstan on the motor shaft and using a
scale with 1/64-inch graduations, position the front edge
(top) of the capstan 1-1/32 (±1/64) inch from the motor
mounting surface. (See figure 4-1.)
e. Tighten capstan set-screws and reinstall capstan
motor assembly .
f. Reconnect capstan motor and tachometer connec-
tors to capstan servo printed-circuit assembly.
Figure 4-1. Capstan PositiEll1
4-12. CAPSTAN (37.6 - 45 IPS UNITS ONLY).
4-13. The capstan replacement for 37.6 - 45 ips units is
the same as the 10 - 37.5 ips units except that a single screw
secures the capstan to the motor shaft. The capstan position
on the shaft is not adjustable.
4-14. REEL HOLDDOWN- ASSEMBLY.
4-15. The replacement of the reel holddown assembly is
not critical; however, an adjustment of the reel retaining
knob must be made to ensure that the tape reel mounts
firmly and does not slip. Refer to section V for a descrip-
tion of the reel retaining knob adjustment.
4-16. TENSION ARM ASSEMBLY.
4-17. The replacement of the tension arm assembly is not
critical; however, the tape rollers are critical to preloading.
The following procedures describe replacing the tension arm
assembly.
a. Disconnect the tension arm photosense connector
from the reel servo assembly.
Part 2