TROUBLESHOOTING
GUIDE
When
0
defect
occurs
in On electronic
circuit
the firs
t
component
suspected
is usually
the vacuum tube. Many of
the inexpensive
tube teste
r
s
will not indicate
all the possible
~ internal
faults
in a voeuum tube - sli ght defects
often sneak
past these
t
e
sters.
It is b
et
ter to subst
i
tut
e
another
tube of
the same typ
e
.
Sometimes
j
t
i
s possi bl
e
to swi tch (transpose)
t
ub
e
s from
one circuit
to another.
This
.
method of testing
is most suitable
when testing
an
individual
stereo
channel.
When a good tube
is switched
with
0
defec
t
i
v
e
One of the SOme type the symptom
will be'ransferred
from one stereo
channel
to the other.
When substitut
i
ng
tub
e
s
i
t
is absolutely
necessary
to be
cer
t
ain
t
he tube being inserted
is
·
good - a new
t
ube, from a
fr
e
sh Iy opened carton,
is not necessa
r
i
Iy a perfect
tub
e.
D
e
-
fec
t
s ",an occur from shipping
and
h
a
n
dling
.
If you have any doubts
about the quality
of a
t
ub
e
try it
i
n an identical
'
e
i
rcuit
that is ope
r
ating
properly.
For example
,
a tube with heoter-ea
th
ode
leakage
may operate
normally
in a
circuit
with its cathode
grounded;
transpOSe
(swi
t
ch)
it with
One in a circuit
tha
t
has a cathode-b
i
as
resistor
and it will
cause
a lo
t
of hum
.
•
AC-interloek
plug
and
,..,eket,
power cord and plug. wall ou
t
l
e
t.
•
Automatic
shut~ff
sw
i
tch
51 (par
t
of SELECTOR
s
wi
tch)
•
Power
s
witch
54
.
•
Automatic
shut
-
off
switch
5
1
(par
t
of SELECTOR
switch)
.
•
J9 and its plug and
t
h
e
interconnecting
cable and th
e
turntabl
e
sw
it
ch o
n t
h
e
record player.
Di
s
to
r
tion
Hum, Weak or
No oudio output
Check:
•
SPKR swi
t
ch
position
and its operation
.
Test
or
.
subst
i
tut
e
VI. Test for p
r
op
er
DC voltages
a
t:
CR2, C2, R3; R3
,
R6
,
C3B; R6, R7, C3C;
R7, C3D
.
•
Setting
of HUM ADJUST CONTROL
(R2).
•
29S
-
volt
DC
'
pow
e
r supply
fi I
t
er (C3A, B, C, 0 ),
•
Bios supply
(CR3 an
d
C4) fo
r
AC ripple.
DistortIon
Hum, Weak or
No
'
C
udi
a
outpu
t
(
LEFT
ehonnel
only) SELECTOR
In
P
H
ONO
nod FM po
s
itions.
•
Remov
e
plug
f
rom Ll;FT
RCRDR OUT jock, if used.
Test
(filament
l
eakage
for hum) Or
s
ubstitu
t
e
VI,
V4,
VS.
Hum or
No aud
i
o output
(
RIGH
T
channel
only) SELEC
T
OR
in PHON
O
and FM positions
.
•
Remove plug f
r
om RIGHT RCRDR OUT jock,
i
f used.
Test
(fi lament
leokage
fo
r
hum) or substitut
e
VI,
V4,
V5.
Hum or
S
ELECTOR
in PHONO po
s
ition
s
on
l
y
No audio output
•
J3, J7, J9 and their plug
s
and interconnect
i
ng
c
ables
t
o th
e
r
e
co
r
d player.
•
Clean and t
i
gh
te
n
oil g
r
ound connections.
.
•
R
e
vers
e
AC
li
ne-card
p
lug in wall ou
t
let
•
Rev
e
rse
AC l
i
ne-eord
plug from record
player
i
n J
1
8 (on chassis)
if u
se
d
.
Hum o
r
No audio outpu
t
S
EL
EC
TOR
i
n
FM position
o
n
l
y.
•
Try other stations
•
Reverse
AC line.cord
pl
u
g
i
n wall ou
t
l
e
t.
Ch
e
ck
:
•
An
t
enna
connection
s
and ant
e
n
n
a
(outdoor)
T
e
st
(
f
i
l
ament
leakage
for hum) o
r
subst
it
u
t
e
Vll,
V
1
2, V13, V14.
Hum-
No aud
i
o output
Di
s
tortion
Ch
e
ck
:
•
Balanc
ed
modulato
r
0401 and C409, C410; C407
,
C412i
L401,
L402.
Test
(filament
leakage
for hum) or subst
i
tut
e
V401, V402.
.
•
IS. V402, C406, R433, R434, R43S, CR402, CR401
.
•
A li9nm
e
nt of Z421
.
