Sansui AU-70 - Service Note

SERVICE NOTE
Symptom
No power when power switch is
pushed on
Probable Cause
1./ Defective power switch .
2.
Defective line cord .
Replace .
Replace .
What to Do
3. Loose contact betwe en plug and socket or R eco ndition or re pla ce .
defective plug .
4. Blown fuse. Replace .
Power indicator is lit when power
switch is pushed on. but;
A. the unit does not work at all. 1. Def e ctive tube.
2. Abnormal voltage in tubes and o ther parts .
B .
PNONO and TAPE does not
fu nction.
1.
Defective head amplifier ( transistor section ).
2.
Defective selector switch.
3.
Loose contact or short - circuit between input
terminal and pin - jack .
4.
Defective record pla ye r.
tape
recorder. or
others. connected to the
unit.
5.
Defective coupling condenser .
C. Weak sound
on
AUX . 1.
Abnormal
voltage
in power circuit and
PHONO and TAPE .
other parts.
A. Normal voltage at ' eve ry part 1. Defective fixed resistance .
but weak sound on AUX
2. Short -c ircuit in ou tput transformer.
3. Discharged capacitor.
4. Aged tube .
5.
Defecti ve slide switch or selector switch .
I
,
If again blown after replacing. check power
transformer ( T, ) & path condenser (C
s
,) in
power circuit for short-circuit.
Check V , ~ V 9 and silicon diodes.
Check voltage in tube and other parts and
replace. if necessary . If voltage is OK. check
AUX input circuit and hereafter.
Rep l ace
transistor
head amplifier unit.
Replace
or
repair S2'20 and / or S2e. S 2f
Replace or
repair.
Replace .
Re
plac e C,
and / or Cs.
Check and repair .
Check R ,,~ R ,s . R 66~ R" and Compound part
CRS01. CRS02.
Check C 2 ' ~ C Z " C
a6
and C
a
, tubular electro -
ly tic capacitor C
2
,. C
26
. C.
o
.
C" .
-- -------------------+---------------- ------- ------ ~------------------------ -- ---
I
B. Normal voltage at every part 1. Defective selector switch .
but weak sound on PHONO
and TAPE .
2. Abnormal input circuit :
between input terminal
defective shielded wire .
loose contact
and pin · jack:
3.
Defecti ve
record pla y er . tape recorder or
others. connected to the unit .
4.
Defecti ve coupling condenser.
5.
Discharged by pass condenser.
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Replace or repair S 2" S 20. S 2e . Sz f. S". and
S JO
Repla ce or r epa ir.
Replace
Check C ,. C
z
•
C,.
C
6
• C, . and
Cs.
Check
Cs.
C,.
C
9
•
and C 'O .
Symptom
A . Distorted so und on AUX.
B. Distorted sound on PHO NO
and TAPE.
A . Hum on AUX .
Probable Cause
What to Do
1. Aged tube .
Check V ,~ V 9 '
2. Short -c ircuit In output transformer .
Check and repair T z and T 3
3. Defecti ve loudspeaker. Replace .
4. Defective record pla y er. adapto r or others. Replace
connected to the unit.
l. Defecti ve record pla ye r. tape rec order or Replace .
o
th e rs . connected to the unit.
2. De fecti ve tubular elect r oly tic capacito r.
3. Di
scon ne c tion at fixed resistance .
l. Electrol ytic capacit or di scharged .
2. D
efec t ive tube.
Replac e C, and / or C
2
.
Chec h R 2 , ~ R az . R •. R,a. R ... R
15
• R '6 . R
17
• R'B.
R '
9. R
zo
. R
2
, and R
22
.
Check C
a
,. C66 ~ C' 3 . C76~C77'
Check V, ~ V 9.
3. Def ective record pla ye r. ada pt or or others. R ep lac e.
connected to the unit.
4. Hum balancer not properl y a dj uste d. Check VR .. a nd VR ".
5. Dis connected NF r esistor. Ch eck RS2 and R
s3
.
B . Hum on PHONO and TAPE. l. D efec tive shielded wire and / or wrong con- Replace a nd connect correctly
nection of record pla ye r. tape reco rder or
others .
2. Audio system and shielded wire induced
f rom outside .
3.
Residual hum of audio sys tem co nnected
to the unit.
A . Noise on AUX and TUNER . 1. Fix ed resistor badly connected or touched
by a nother part .
Keep prop er dis tance between audio system
and inductor.
Replace or repair.
. 2. Capacitor nearly short- cir cui ted or touched Check C'6. C
S7
• C
60
•
C
6
, .
by another part.
3. Primar y coil of output transformer nearly Check T z and T a.
dis co nnected.
4. Defecti ve tube . Check V, ~ V 9.
B . Noise on RHONO and T A PE . 1. Fixed resistor defective or ne a rly discon- Check R 7~ R a2
nected.
2. Defecti ve capacitor. Check C ,~ClO
3. Noise or bad connection of audio system Replace or repair
connected to the unit.
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