Pcb Inspection - Samsung MH020FPEA Service Manual

6-4 PCB Inspection

6-4-1 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. When soldering the lead wires of any new part, be sure
to polish them using an emery paper or the like before
soldering 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.
6-4-2 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
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 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.
9. Although some part of the PCB surface are coated with
coating material for protection from dust and dirt,
soldering is also available to the coating part. Because
this coating is thin and is weak for soldering heat.
But coating material remaining on the solder part should
be cleaned up before soldering a new component to
prevent the solder part from becoming bad conduction.
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