Sharp 8C221, Service Manual

Page: 19 / 46

These notes may give the impression that the repair of
and sets is a complicated procedure.
,
However, no difficulties should be encountered provided
that it is remembered that extra care must be taken in
to valve-operated receivers.
EXAMPLES OF DEFECTIVE PARTS
Transistors
(a) Short-circuit of connections . . . Continuity in
both forward and backward directions when
measured by an ohmmeter.
Burn-out of connections (open) . . . No continuity
in both forward and backward directions when
measured by an ohmmeter.
Deterioration of characteristics.
Capacitors
(a) Change of capacity
No capacity (open)
Defective insulation (leak)
Short-circuit
Resistors
(a) Increase of resistance value
Generally, resistances tend to increase in value
during use. This often occurs in cases of higher
resistances than
ohms.
B u m - o u t
Resistance value is extremely increased.
Coil, Transformers
(a) Burn-out
Layer short line short iron core short . . . etc.
CHECKING OF TRANSISTORS BY OHMMETER
Transistors can be checked by measuring the forward
backward resistances between collector and base,
emitter and base. and
and
Since the function of a diode exists between emitter and
base, collector and base, low and high resistances are
indicated by polarity when measured with a test meter.
The former is the resistance and the latter is the
backward resistance.
Attention must be paid to the range of the ohmmeter.
In the case of an ordinary transistor, the range can be
found by
but the range of a power transistor must
be reduced for the measurement. Alteration of resistance
values measured by tester.
Short-circuit of connections . . . Both forward and
backward resistances become zero.
Burn-out of connections (OPEN) . . . Both forward
and backward resistances become infinite.
Deterioration of characteristic . . . Difference between
forward and backward becomes small.
Note: It is desirable to measure the transistor whilst
disconnected from the
, ,
R LEAK
LAYER SHORT
LAYER LEAK
I
SHORT
Figure
LAYER SHORT
Figure
BURN-OUT