+Oetailed
Troubleshooting Procedures When
PA
Fails:
..,
When PA fails (1)
Phenomena: Short circuit between VOO
of
PA
and the ground.
Gauses
:(1
)One
of
bypass capacitors
C14
to
C19
or
C24
to
C29
of CAH-377
power amplifier has short-circuited.
(2)0ne
of FETs TR11 to TR1
E?.
TR21 to TR26, TR31 to TR36 or TR41
to TR46 of CAH-377 power amplifier has short-circuited between
drain
(0) and source (S).
(3)0thers
< Troubleshooting procedures >
(1
)Remove the
two
fuses (15 A each) from between the
PA
unit
and
power
supply unit.
(2)Check.
two
CAH-377
power
amplifiers
for
the
electric
conductivity between VDO and
the ground with a tester to find which one is out
of
order. ln the normal state, the
electric conductivity between VOO and the ground shows diode characteristics
(cathode: VOO, anode: ground).
(3)Check the external appearance
of
the bypass capacitors
or
FETs
of
the failed CAH-
377 power amplifier for damage, etc.
(4) ln the case
of
a short circuit between drain (0) and source (S)
of
FET, check the
resistance value between gate (G)
and
source (S)
to
locate the failed FET because
in most cases between gate (G) and source (S) has short-circuited. As
shown
in
Fig. 12, in
the
case
of
a short-circuit between gate (G) and source (S), the resis-
tance value between gate
(G) and source (S)
of
each TR12 to TR16 is about 54
n.
lf
all FETs are normal,
the
resistance value between gate (G) and source (S)
of
each
FET
is
about
1 0 k n .
Fig.12
24
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