Hitachi 36UX59B Service Manual page 6

MSLXU
Fuses and conventional Resistor Removal/Replacement
Clip each fuse or resistor lead at top of circuit board hollow
stake.
Securely crimp leads of replacement component around stake
l/8 inch from top.
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 "lift-off" 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 area 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 fol-
lowing 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.
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.
At Other Connections
Use the following technique to repair defective copper pattern at
connections other than IC Pins. This technique involves the instal-
lation of a jumper wire on the component side of the circuit board.
Insulated Jumper Wire
1. Remove the defective copper pattern with a sharp knife.
Remove at least l/4 inch of copper, to ensure hazardous con-
dition will not exist if the jumper wire opens.
2. Trace along the copper pattern from both wire sides of the pat-
tern break and locate the nearest component directly con-
nected 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 sol-
der the connections.
CAUTION: Be sure the insulated jumper wire is dressed so
that it does not touch components or sharp
edges.
Frequency Synthesis (FS) Tuning Systems
Always unplug the instrument AC power cord before discon-
necting or reconnecting FS tuning system cables and before
removing or inserting FS tuning system modules.
The FS tuner must never be disconnected from the FS tuning
control module while the power is applied to the instrument.
When troubleshooting intermittent problems that might be
caused by defective cable connection(s) to the FS tuning sys-
tem, remove the instrument AC power as soon as the defec-
tive connector is found and finish confirming the bad connec-
tion with a continuity test. This procedure will reduce the prob-
ability of electrical overstress of the FS system semi-conduc-
tor components.
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.
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