Samsung MC18AC2-09 Service Manual page 32

5-3 PCB Inspection
5-3-1 Cautions for Part Replacement
1. The human body carries much static
electricity. Before touching a part for
repair, replacement or the similar purpose,
be sure to touch a grounded metallic
portion by hand to let the static electricity
go through the metallic portion to the
earth.
Especially when handling any micro
computer or IC, carefully remove such
static electricity before touching them.
2. When repairing any part on a work bench,
be sure to place an insulative sheet on the
bench and always keep the sheet surface
neat without any metal fragments. If any
such fragment touches a part, a secondary
trouble will possibly be caused in the part.
3. Before replacing any parts, be sure to turn
off the power supply. If such replacement
is done with the power supply kept on, an
electric shock, short circuit or destruction
of a part may result.
4. During replacement or repair of a part,
carefully handle it : The printed circuit
board has fine lead wires (jumper wires)
and glass-made parts (diode) on its
substrate.
So if a circuit board is roughly handled,
such lead wires and parts will be easily
broken or damaged by bending or shock.
5-3-2 Procedure
The parts should be replaced in the following procedure.
Check for any faulty part.
Detach the faulty part.
Replace it with a new part.
Check the operation of the new part.
The repair is completed.
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5. When soldering the lead wires of any new
part, be sure to polish them using an
emery paper or the like before solding
them.
Since the lead wires of any new part are
covered with an oxide film, solder cannot
adhere to the lead wires if not polished.
6. When soldering any part, care should be
exercised not to apply any high-wattage
soldering iron to the part for a long time.
Some parts are of so low a heat resistance
that they may be broken or have the
properties changed if a soldering iron is so
applied (Otherwise, the pattern may
possibly be separated and raised).
7. The heat of the soldering iron should be
transferred to the entire object to be
soldered. If the solder pieces are not well
fused due to insufficient transfer of the
heat from the soldering iron, no satisfacto-
ry electrical continuity can be assured
even if the soldered objects appear well
connected to each other.
8. The solder used should be limited to a
minimum. If excessive solder is used, it
will cause inter-pattern contact, which
may cause malfunction of the circuit.
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