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7970B/7970C
Repair and Replacement
SECTION IV
REPAIR AND REPLACEMENT
4-1.
INTRODUCTION.
4-2.
This section provides repair and replacement pro-
cedures for the tape transport of the HP 7970B/7970C Dig-
ital Magnetic Tape Units.
a. Avoid unnecessary component substitution; it can
result in damage to the PCA circuit board and/or adjacent
components.
b. Do not use a high·power soldering iron. Excessive
heat may lift a conductor or damage the board.
4-3.
REPAIR.
CAUTION
Do not use a sharp metal object such as an awl
or twist drill to remove solder. Sharp objects
may damage the plated-through conductor.
4-4.
The etched printed-circuit assemblies (PCA's) used
are of the plated-through type consisting of metal bonded
to both sides of an insulating material. The metallic con-
ductors are extended through the component holes by a
plating process. Soldering can be performed on either side
of the PCA with equally good results. Table 4-1 lists recom-
mended tools and materials for use in repairing etched PCA's.
The following are recommendations and precautions pertin-
ent to PCA repair work.
c. Use a suction device (table 4-1) or wooden tooth-
pick to remove solder from component mounting holes.
d. After soldering, remove excess flux from the solder
areas and apply a protective coating to prevent contamina-
tion and corrosion.
Table 4-1. Printed-Circuit Assembly Repair Equipment
ITEM
USE
DESCRIPTION
RECOMMENDED MODE L
Soldering Tool
Soldering and unsoldering
Wattage rating: 47-1/2 to 56-1/2W
Ungar #776 Handle with
Tip Temp: 850
0
to 900°F
Ungar #4037 Heating Unit*
Soldering Tip*
Soldering and unsoldering
Shape:
pointed
Ungar #PL111*
Suction Device
Removes
molten
solder
Soldapullt by Edsyn Co.,
from connection
Arleta, California
Resin (Flux)
Removes excess flux from
Must not dissolve etched circuit
Freon
Solvent
soldered area before appli-
base board material or conductor
Aceton
cation of protective coating
bonding agent
Lacquer Thinner
Isopropyl Alcohol (100% dry)
Solder
Component
replacement,
Resin (flux) core, high tin content
printed-circuit board repair,
(60/40 tin/lead), 18 gauge (SWG)
and wiring connections
preferred
Protective
Contamination and corro-
Good
electrical
insulation,
Krylon R** #1302
Coating
sion protection
corrosion-prevention properties
Humiseal Protective Coating,
Type 1 B 12 by Columbia
Technical Corp., Woodside 77,
New York
*For working on etched boards; for general purpose work, use Ungar #1237 Heating Unit (37.5W, tip temp of 750°
to 800° F) and Ungar #P L 113 1 /8-i nch ch isel ti p.
** Kryton, Inc., Norristown, Pennsylvania
Part 2
4-1
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