Philips 190E2FB/00 (AP), Service Manual

Page: 85 / 90

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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
potential!
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 solde r (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)
While holding the SMD with a pair of tweezers, take it off gently using
the soldering iron's heat applied to each terminal (see Fig. 1 B).
- Remove the excess solder on the solder lands by means of litz wire or
a solder sucker (see Fig. 1C).
While holding the SMD with a pair of tweezers, take it off gently using
the soldering iron's heat applied to each terminal (see Fig. 1 B).
- 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 handling the soldering.iron. use suitable pressur e and be
careful.
- When removing the chip, do not use undue force with the pair of
tweezers.
- The soldering iron to be used (approx. 30 W) should preferably be
equipped with a thermal control (soldering temperature: 225 to 250 C).
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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
Fiq. 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. 30 W ) should preferably be
equipped with a thermal control (soldering temperature: 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).
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