Hitachi UT47X902 Service Manual page 7

Fuses and Conventional Resistor Removal/
Replacement
1. Clip each fuse or resistor lead at top of circuit board
hollow stake.
2. Securely crimp leads of replacement component around
stake 1/8 inch from top.
3. Solder the connections.
CAUTION: Maintain original spacing between the
replaced component and adjacent components and
the circuit board, to prevent excessive component
temperatures.
Circuit Board Foil Repair
Excessive heat applied to the copper foil of any printed
circuit board will weaken the adhesive that bonds the
foil to the circuit board, causing the foil to separate
from, or "liftoff," the board. The following guidelines and
procedures should be followed whenever this condition is
encountered.
in Critical Copper Pattern areas
High component/copper pattern density and/or special
voltage/current characteristics make the spacing and
integrity of copper pattern in some circuit board areas
more critical than in others. The circuit foil in these areas
is designated as Critical Copper Pattern. Because Critical
Copper Pattern requires special soldering techniques to
ensure the maintenance of reliability and safety standards,
contact your Hitachi personnel.
at iC Connections
To repair defective copper pattern at IC connections, use
the following procedure to install a jumper wire on the
copper pattern side of the circuit board. (Use this technique
only on IC connections.)
1. Carefully remove the damaged copper pattern with a
sharp knife. (Remove only as much copper as absolutely
necessary.)
2. Carefully scratch away the solder resist and acrylic
coating (if used) from the end of the remaining copper
pattern.
CRIMP AND
SOLDER
Install jumper wire and solder.
3. Bend a small "U" in one end of a small-gauge jumper
wire and carefully crimp it around the IC pin. Solder the IC
connection.
4. Route the jumper wire along the path of the cut-away
copper pattern and let it overlap the previously scraped
end of the good copper pattern. Solder the overlapped
area, and clip off any excess jumper wire.
BARE JUMPER
WIRE
at other Connections
Use the following technique to repair defective copper
pattern at connections other than IC Pins. This technique
involves the installation of a jumper wire on the component
side of the circuit board.
DEFECTIVE
COPPER
REMOVED
Insulated jumper wire
1. Remove the defective copper pattern with a sharp knife.
Remove at least 1/4 inch of copper, to ensure hazardous
condition will not exist if the jumper wire opens.
2. Trace along the copper pattern from both wire sides of
the pattern break and locate the nearest component directly
connected to the affected copper pattern.
3. Connect insulated 20-gauge jumper wire from the nearest
component on one side of the pattern break to the lead of
the nearest component on the other side.
Carefully crimp and solder the connections.
CaUtion: Be sure the insulated jumper wire is dressed so
that it does not touch components or sharp edges.
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