TROUBLE SHOOTING GUIDE
Methods of Checking
Repairs will be considerably simplified by careful observa-
tion of the defect and its location to a specific part of the
circuit.
Once this has been done it can be said that
of the repair has been completed.
To do this an understanding of the outline of the
used
in solid state
T.V. will be of great assistance in
quickly
diagnosing the cause of trouble.
When checking, the following procedure is
Carefully note the symptoms of the trouble. Ensure
that the defect is in fact caused by the receiver and not
by a fault in transmission, by switching to alternative
channels.
If the fault is present on all channels locate the defective
circuit in the receiver.
Where the defective circuit has adjustable controls
ensure that these are correctly set. If adjustments have
no effect on the fault be sure to
to the original
positions.
Measure voltages and waveforms of the suspected circuit
block and, if defects are found, replace the transistors,
or other components.
(a) Check the collector voltage and waveform of
transistors.
Check voltage between base and emitter of
transistors.
(Generally
1 v for silicon
transistors and
v for germanium tran-
sistors).
Measure the terminal voltages and waveforms of
Check resistors, capacitors and coils.
Note:
When removing components from the
dis-
connect the leads by heating the soldered portions
with a soldering iron, removing surplus solder
with a
tool.
PART
COPPER FOIL
TOOL
Melt the solder and suck it
up by the
tool.
Figure
PRECAUTIONS TO BE TAKEN DURING
In servicing, some of the methods used for valve systems
do not work on solid state
T.V. receivers. Keep in
mind
Transistors and
MUST NOT be overloaded, even
momentarily.
In the case of valves, damage is rarely caused even if the
anodes and screens are severely overloaded, provided
that this condition is not maintained for very long.
Transistors and
however, should not be subjected
to overload even for a moment.
Be sure to switch off the power source when removing
or soldering leads or measuring resistance.
Essential Conditions in Checking Transistors
The test and replacement of power transistors must be
carried out in such a way that the transistor is kept in
its heat-sink.
Valve checking is simple but with tran-
sistors testing is complicated by the fact that screws and
solder must be removed. Never test a power transistor
which is not securely fixed in its heat-sink otherwise
damage will be caused by overheating as power tran-
sistors consume large current.
To check small transistors, remove as quickly as possible
with a soldering iron avoiding excessive heating of the
transistor.
Avoiding short-circuits
When checking voltages or waveforms take care not to
produce shortcircuits with the test probes or test clips
of the meter or oscilloscope.
During operation:
DO NOT short the emitter resistor.
DO NOT short or open circuit the bias resistor.
DO NOT short the collector resistor.
DO NOT allow adjacent legs of
to come into contact
with each other.
Do Not Operate Vertical Output Circuit With Parts
Removed.
If the vertical output circuit is operated with parts
removed a large
pulse may be produced which
can cause
or deterioration of transistors.
In checking the horizontal deflection circuit, abnormal
oscillation such, as sparking the high voltage circuit and
stopping the oscillator circuit must be avoided.
If the high voltage circuit is checked by sparking the
driver or the input pulse is cut off abruptly with the
horizontal output circuit operated, the output transistor
may be damaged.
The output transistor is designed to
withstand high voltages but if it is heated or subjected
to abnormal conditions for long periods the resistance
against voltages’ will be considerably reduced, and the
transistor may be damaged if subjected to an input
circuit shock (cutting off the input instantly) or output
circuit shock (sparking the high voltage circuit).
Others
Wires must be carefully arranged after check and repair.
(Be sure to connect them to the original places taking
care not to induce high voltages or other circuitry).
Summary of Contents for 8C221
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