Repair Tips - Philips TFT LCD Colour Monitor Service Manual

42 190B4 LCD
0. Warning
All ICs and many other semi-conductors are susceptible to
electrostatic discharges (ESD). Careless handling during repair
can reduce life drastically. When repairing, make sure that you
are connected with the same potential as the mass of the unit
via a wrist wrap with resistance. Keep components and tools
also at the same potenial !
1. Servicing of SMDs (Surface Mounted Devices)
1.1 General cautions on handling and storage
- Oxidation on the terminals of SMDs results in poor
soldering. Do not handle SMDs with bare hands.
- Avoid using storage places that are sensitive to
oxidation such as places with sulphur or chlorine gas,
direct sunlight, high temperatures or a high degree of
humidity. The Capacitance or resistance value of the
SMDs may be affected by this.
- Rough handling of circuit boards containing SMDs may
cause damage to the components as well as the circuit
boards. Circuit boards containing SMDs should never be
bent or flexed. Different circuit board materials expand
and contract at different rates when heated or cooled
and the components and/or solder connections may be
damaged due to the stress. Never rub or scrape chip
components as this may cause the value of the
component to change. Similarly, do not slide the circuit
board across any surface.
1.2 Removal of SMDs
- Heat the solder (for 2-3 seconds) at each terminal of the
chip. By means of litz wire and a slight horizontal force,
small components can be removed with the soldering
iron. They can also be removed with a solder sucker
(see Fig. 1A)
Fig. 1 DISMOUNTING
- While holding the SMD with a pair of tweezers, take it off
gently using the soldering iron's heat applied to ezch
terminal (see Fig.1B).
- Remove the excess solder on the solder lands by
means of litz wire or a solder sucker (see Fig. 1C).
1.3 Caution on removal
- When handing the soldering.iron. use suitable pressure
and be careful.
- When removing the chip, do not use undue force with
the pair of tweezers.

Repair Tips

- The soldering iron to be used (approx. 30W) should
preferably be equipped with a thermal control (soldering
temperature: 225 to 250¢ J )
- The chip, once removed, must never be reused.
1.4 Attachment of SMDs
- Locate the SMD on the solder lands by means of
tweezers and solder the component on one side. Ensure
that the component is positioned correctly on the solder
lands (see Fig.2A).
- Next complete the soldering of the terminals of the
component (see Fig. 2B)
2. Caution when attaching SMDs
- When soldering the SMD terminals, do not touch them
directly with the soldering iron. The soldering should be
done as quickly as possible, care must be taken to avoid
damage to the terminals of the SMDs themselves.
- Keep the SMD's body in contact with the printed board
when soldering.
- The soldering iron to be used (approx. 30W) should
preferably be equipped with a thermal control (soldering
temperature¡ G 225 to 250 C).
- Soldering should not be done outside the solder land.
- Soldering flux (of rosin) may be used, but should not be
acidic.
- After soldering, let the SMD cool down gradually at room
temperature.
- The quantity of solder must be proportional to the size of
the solder land. If the quantity is too great, the SMD
might crack or the solder lands might be torn loose from
the printed board (see Fig. 3).
Fig. 2 MOUNTING
Fig. 3 Examples