3
Safety instructions, Maintenance instruction,
4
3
Safety instructions, Maintenance instruction, Warnings and Notes
3.1
Safety instructions for repairs
Figure 3-1
1.
Safety regulations require that during a repair:
–
the set should be connected to the mains via an
isolating transformer;
–
safety components, indicated by the symbol (see fig.
3.1), should be replaced by components identical to
the original ones;
–
when replacing the CRT, safety goggles must be worn.
2.
Safety regulations require that after a repair the set must
be returned in its original condition. In particular attention
should be paid to the following points.
–
As a strict precaution, we advise you to resolder the
solder joints through which the horizontal deflection
current is flowing, in particular:
•
all pins of the line output transformer (LOT);
•
fly-back capacitor(s);
•
S-correction capacitor(s);
•
line output transistor;
•
pins of the connector with wires to the deflection
coil;
•
other components through which the deflection
current flows.
Note: This resoldering is advised to prevent bad
connections due to metal fatigue in solder joints and is
therefore only necessary for television sets older than
2 years. The wire trees and EHT cable should be
routed correctly and fixed with the mounted cable
clamps.
–
The insulation of the mains lead should be checked for
external damage.
–
The mains lead strain relief should be checked for its
function in order to avoid touching the CRT, hot
components or heat sinks.
–
The electrical DC resistance between the mains plug
and the secondary side should be checked (only for
sets which have a mains isolated power supply). This
check can be done as follows:
•
unplug the mains cord and connect a wire between
the two pins of the mains plug;
•
set the mains switch to the on position (keep the
mains cord unplugged!);
•
measure the resistance value between the pins of
the mains plug and the metal shielding of the tuner
or the aerial connection on the set. The reading
should be between 4.5 MW and 12 MW;
•
switch off the TV and remove the wire between the
two pins of the mains plug.
–
The cabinet should be checked for defects to avoid
touching of any inner parts by the customer.
3.2
Maintenance instruction
It is recommended to have a maintenance inspection carried
out by a qualified service employee. The interval depends on
the usage conditions:
–
When the set is used under normal circumstances, for
example in a living room, the recommended interval is 3 to
5 years.
–
When the set is used in circumstances with higher dust,
grease or moisture levels, for example in a kitchen, the
recommended interval is 1 year.
–
The maintenance inspection contains the following actions:
•
Execute the above mentioned 'general repair
instruction'.
•
Clean the power supply and deflection circuitry on the
chassis.
•
Clean the picture tube panel and the neck of the picture
tube.
3.3
Warnings
1.
ESD
All ICs and many other semiconductors 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 set by a wristband with resistance. Keep
components and tools also at this same potential.
–
Available ESD protection equipment:
–
anti-static table mat (large 1200x650x1.25mm) 4822
466 10953
–
anti-static table mat (small 600x650x1.25mm) 4822
466 10958
–
anti-static wristband 4822 395 10223
–
connection box (3 press stud connections, 1 M ohm)
4822 320 11307
–
extension cable (2 m, 2 M ohm; to connect wristband
to connection box) 4822 320 11305
–
connecting cable (3 m, 2 M ohm; to connect table mat
to connection box) 4822 320 11306
–
earth cable (1 M ohm; to connect any product to mat or
connection box) 4822 320 11308
–
complete kit ESD3 (combining all 6 prior products -
small table mat) 4822 310 10671
–
wristband tester 4822 344 13999
2.
In order to prevent damage to ICs and transistors, all high-
voltage flashovers must be avoided. In order to prevent
damage to the picture tube, the method shown in Fig. 3.2
should be used to discharge the picture tube. Use a high-
voltage probe and a multimeter (position DC-V). Discharge
until the meter reading is 0V (after approx. 30s).
3.
Together with the deflection unit and any multipole unit, the
flat square picture tubes used from an integrated unit. The
deflection and the multipole units are set optimally at the
factory. Adjustment of this unit during repair is therefore not
recommended.
4.
Be careful during measurements in the high-voltage
section and on the picture tube.
5.
Never replace modules or other components while the unit
is switched on.
6.
When making settings, use plastic rather than metal tools.
This will prevent any short circuits and the danger of a
circuit becoming unstable.
7.
Wear safety goggles during replacement of the picture tube
3.4
Notes
1.
The direct voltages and oscillograms should be measured
with regard to the tuner earth , or hot earth as this is called
(see fig. 3.3)
2.
The direct voltages and oscillograms shown in the
diagrams are indicative and should be measured in the
Service Default Mode (see chapter 8) with a colour bar
signal and stereo sound (L:3 kHz, R:1 kHz unless stated
otherwise) and picture carrier at 475.25 MHz.
Summary of Contents for 286NS-05
Page 14: ...10 Direction for use 28 Comet 10 Direction for use ...
Page 15: ...10 Direction for use 29 Comet ...
Page 16: ...10 Direction for use 30 Comet ...
Page 17: ...10 Direction for use 31 Comet ...
Page 18: ...10 Direction for use 32 Comet ...
Page 19: ...10 Direction for use 33 Comet ...
Page 20: ...10 Direction for use 34 Comet ...
Page 25: ...6 Overview oscillograms 10 Comet ...
Page 34: ...7 Electrical diagrams and print lay outs 19 Comet CL 86532029_008 eps 240698 ...