Safety Instructions, Warnings, and Notes
2.
2.
Safety Instructions, Warnings, and Notes
Index of this chapter:
2.1 Safety Instructions
2.2 Warnings
2.3 Notes
2.1
Safety Instructions
Safety regulations require the following
during
a repair:
•
Connect the set to the Mains (AC Power) via an isolation
transformer (> 800 VA).
•
Replace safety components, indicated by the symbol
h
,
only by components identical to the original ones. Any
other component substitution (other than original type) may
increase risk of fire or electrical shock hazard.
Safety regulations require that
after
a repair, the set must be
returned in its original condition. Pay in particular attention to
the following points:
•
Route the wire trees correctly and fix them with the
mounted cable clamps.
•
Check the insulation of the Mains (AC Power) lead for
external damage.
•
Check the strain relief of the Mains (AC Power) cord for
proper function.
•
Check the electrical DC resistance between the Mains (AC
Power) plug and the secondary side (only for sets that have
a Mains (AC Power) isolated power supply):
1.
Unplug the Mains (AC Power) cord and connect a wire
between the two pins of the Mains (AC Power) plug.
2.
Set the Mains (AC Power) switch to the "on" position
(keep the Mains (AC Power) cord unplugged!).
3.
Measure the resistance value between the pins of the
Mains (AC Power) plug and the metal shielding of the
tuner or the aerial connection on the set. The reading
should be between 4.5 Mohm and 12 Mohm.
4.
Switch "off" the set, and remove the wire between the
two pins of the Mains (AC Power) plug.
•
Check the cabinet for defects, to prevent touching of any
inner parts by the customer.
2.2
Warnings
•
All ICs and many other semiconductors are susceptible to
electrostatic discharges (ESD
w
). Careless handling
during repair can reduce life drastically. Make sure that,
during repair, you are connected with the same potential as
the mass of the set by a wristband with resistance. Keep
components and tools also at this same potential. Available
ESD protection equipment:
–
Complete kit ESD3 (small tablemat, wristband,
connection box, extension cable and earth cable) 4822
310 10671.
–
Wristband tester 4822 344 13999.
•
Be careful during measurements in the high voltage
section.
•
Never replace modules or other components while the unit
is switched "on".
•
When you align the set, use plastic rather than metal tools.
This will prevent any short circuits and the danger of a
circuit becoming unstable.
2.3
Notes
2.3.1
General
•
Measure the voltages and waveforms with regard to the
chassis (= tuner) ground (
H
), or hot ground (
I
), depending
on the tested area of circuitry. The voltages and waveforms
shown in the diagrams are indicative. Measure them in the
Service Default Mode (see chapter 5) with a colour bar
signal and stereo sound (L: 3 kHz, R: 1 kHz unless stated
otherwise) and picture carrier at 475.25 MHz for PAL, or
61.25 MHz for NTSC (channel 3).
•
Where necessary, measure the waveforms and voltages
with (
D
) and without (
E
) aerial signal. Measure the
voltages in the power supply section both in normal
operation (
G
) and in stand-by (
F
). These values are
indicated by means of the appropriate symbols.
•
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.
2.3.2
Schematic Notes
•
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).
•
Resistor values with no multiplier may be indicated with
either an "E" or an "R" (e.g. 220E or 220R indicates 220
ohm).
•
All capacitor values are given in micro-farads (
µ=
x10
-6
),
nano-farads (n= x10
-9
), or pico-farads (p= x10
-12
).
•
Capacitor values may also use the value multiplier as the
decimal point indication (e.g. 2p2 indicates 2.2 pF).
•
An "asterisk" (*) indicates component usage varies. Refer
to the diversity tables for the correct values.
•
The correct component values are listed in the Spare Parts
List. Therefore, always check this list when there is any
doubt.
2.3.3
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, is being removed, it is
essential when removing an (LF)BGA, that 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 risk 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.
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