Philips A02U AA Service Manual page 5

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The semiconductors indicated in the circuit diagram and in
the parts lists, are interchangeable per position with the
semiconductors in the unit, irrespective of the type
indication on these semiconductors.
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Manufactured under license from Dolby Laboratories.
'Dolby', 'Pro Logic' and the 'double-D symbol', are
trademarks of Dolby Laboratories.
Figure 2-2 Dolby Prologic
2.4.2
Schematic Notes
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All resistor values are in ohms and the value multiplier is
often used to indicate the decimal point location (e.g. 2K2
indicates 2.2 kohm).
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Resistor values with no multiplier may be indicated with
either an "E" or an "R" (e.g. 220E or 220R indicates 220
ohm).
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All capacitor values are expressed in micro-farads (µ= x
10^-6), nano-farads (n= x 10^-9), or pico-farads (p= x 10^-
12).
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Capacitor values may also use the value multiplier as the
decimal point indication (e.g. 2p2 indicates 2.2 pF).
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An "asterisk" (*) indicates component usage varies. Refer
to the diversity tables for the correct values.
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The correct component values are listed in the Electrical
Replacement Parts List. Therefore, always check this list
when there is any doubt.
2.4.3
Rework on BGA (Ball Grid Array) ICs
General
Although (LF)BGA assembly yields are very high, there may
still be a requirement for component rework. By rework, we
mean the process of removing the component from the PWB
and replacing it with a new component. If an (LF)BGA is
removed from a PWB, the solder balls of the component are
deformed drastically so the removed (LF)BGA has to be
discarded.
Device removal
As is the case with any component that, it is essential when
removing an (LF)BGA, the board, tracks, solder lands, or
surrounding components are not damaged. To remove an
(LF)BGA, the board must be uniformly heated to a temperature
close to the reflow soldering temperature. A uniform
temperature reduces the chance of warping the PWB.
To do this, we recommend that the board is heated until it is
certain that all the joints are molten. Then carefully pull the
component off the board with a vacuum nozzle. For the
appropriate temperature profiles, see the IC data sheet.
Area preparation
When the component has been removed, the vacant IC area
must be cleaned before replacing the (LF)BGA.
Removing an IC often leaves varying amounts of solder on the
mounting lands. This excessive solder can be removed with
either a solder sucker or solder wick. The remaining flux can be
removed with a brush and cleaning agent.
After the board is properly cleaned and inspected, apply flux on
the solder lands and on the connection balls of the (LF)BGA.
Note: Do not apply solder paste, as this has shown to result in
problems during re-soldering.
Device replacement
The last step in the repair process is to solder the new
component on the board. Ideally, the (LF)BGA should be
aligned under a microscope or magnifying glass. If this is not
possible, try to align the (LF)BGA with any board markers.
Safety Instructions, Warnings, and Notes A02U AA
To reflow the solder, apply a temperature profile according to
the IC data sheet. So as not to damage neighboring
components, it may be necessary to reduce some
temperatures and times.
2.4.4
Practical Service Precautions
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It makes sense to avoid exposure to electrical shock.
While some sources are expected to have a possible
dangerous impact, others of quite high potential are of
limited current and are sometimes held in less regard.
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Always respect voltages. While some may not be
dangerous in themselves, they can cause unexpected
reactions - reactions that are best avoided. Before reaching
into a powered TV set, it is best to test the high voltage
insulation. It is easy to do, and is a good service precaution.
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Before powering up the TV set with the back cover off
(or on a test fixture), attach a clip lead to the CRT DAG
ground and to a screwdriver blade that has a well insulated
handle. After the TV is powered "on" and high voltage has
developed, probe the anode lead with the blade, starting at
the case of the High Voltage Transformer (flyback - IFT).
Move the blade to within two inches of the connector of the
CRT. If there is an arc, you found it the easy way,
without getting a shock! If there is an arc to the
screwdriver blade, replace the part that is causing the
problem; the High Voltage Transformer or the lead (if it is
removable)
2. EN 5