Realistic STA-85 - Page 16

SYMPTOM CAUSE AND REMEDY
24l, Noisy
VOLUME
control A) Defective VR551
or VR552
Replace the variable
resistor.
B) Defective
capacitor C506,
C901, C905 or C912
Replace the defective
capacitor(s).
25l.
SIGNAL meter not
functioning.
A) Defective
meter
Replace
the meter.
B)
ln
case
of
FM reception, lC2O1,
D2O4 or TH201
defective
Replace the defective
component(s).
C)
ln
case of AM reception, 1C401 or VR401
defective
Replace the defective
component(s).
26l,
AUTO-MAGIC
AFC has
no effect
when
AUTO-M
switch is
ON.
(White
light
behind the
tuning meter
does not
change
to red
when
the
tuning
control is touched.)
A) Transistor TR701
,TR7O2
or lC 1C701 defective
Replace the defective
component(s).
B)
Resistor R706,
R715, R716 or R718 defective
Replace the defective resistor(s).
C) Diode D7O1, D7O2
or
D852 defective
Replace
the defective diode(s).
D) Capacitor
C7O4
or
C705
defective
Replace the
defective capacitor(s).
E)
Defective switch SW2.
Replace the
switch.
271
Red light
does not
light when the
tuning
control is
released.
A) Defective transistor
TR701
(open)
or TR702
(short)
Replace
the defective transistor(s).
281 Hl-FlL
has no
effect.
A)
Defective switch
SW6
Replace
the switch.
B) Defective capacitor
C702
Replace
the
capacitor.
NOTE:
Transistors
TR605 and TR606
protect
the audio output stage when abnormally high current
flows through
TR609
and TR610,
caused by
excessive drive at input, or too
low
impedance
load
is connected
at output.
lf
increase
of
the
current
is
excessive,
the voltage across
R623
and
R626
will
turn
on
TR605 and
TR606
which
are normally not biased
"on".
The
collector
potential
of these transistors
(through
D601 and D602 diodes) reduce bias on
TR607 and
TR608,
which
causes output transistor
current
(TR609
and
TR610)
to reduce.
This
performs
two safety
functions.
1.
Protects
the output
circuit devices.
2.
Protects
the
speakers from loud
clicks,
pops
and
excessive levels.
TO
OBIVT
CIBCUIT
TO
OBIVT
CIRCUIT
16