Pcb Inspection; Cautions For Part Replacement - Samsung AQ07A1VE Service Manual

5-3 PCB Inspection

5-3-1 Cautions for Part Replacement

1. The human body carries much static electrici-
ty. Before touching a part for repair, replace-
ment or the similar purpose, be sure to touch
a grounded metallic portion by hand to let the
static electricity go through the matallic por-
tion 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 with-
out any metal fragments. If any such fragment
touches a part, a secondary trouble will possi-
bly 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, care-
fully 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 cov-
ered with an oxide film, solder cannot adhere
to the lead wires if not polished.
6. When soldering any part, care should be exer-
cised 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 sol-
dering iron is so applied (Otherwise, the pat-
tern may possibly be separated and raised).
7. The heat of the soldering iron should be trans-
fered to the entire object to be soldered. If the
solder pieces are not well fused due to insuffi-
cient 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 mini-
mum. If excessive solder is used, it will cause
inter-pattern contact, which may cause mal-
function of the circuit.
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