Pcb Inspection; Cautions For Part Replacement - Samsung AQ12?5(6)MB Service Manual

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.
Samsung Electronics
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
transfered 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 satisfactory 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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