Service
Manual '41 Models
7800, 7850, 8800
and
9800
A
shorted or defective tube
is often a cause of faulty tone
quality.
A
loose connect.ton at the
terminals or the terminal
on tt.e chassis can s:ffect
the tone quality.
Check the
volUJ!le
control by
rotating i t when a record i s
being
p
l
a
yed.
I
f sudd
e
n c
n
a
n
ges
lr1
volume are notlced, the cause
may be dirt between the contact
arm and resistor in the control,
or a worn resistor.
It is often
possible to remove dir�
or scale
ty
rotat1ng the control back and
forth rapidly.
!f1
after trying
this, the control still causes
sudden changes in volume, when it
is rotated
slowly,
repla
c
ing of
the control is a�visable.
C.
�!OTOR
HUM
Bum is sorr.etimes caused by
the "motor when the
loops
in the
motor mounting springs
{Fig. 4,
No.
1841) touch where they cross.
Thls happens when the spr1ngs be
come damaged in handling and can
be corrected by bendj.ng them so
they do not touch.
D.
HUM DURING
W.i\Rff,U.P
PERIOD
On
some
of
the earlier type
825-5
and 825-lO amplifiers. a
slight hum was noticeable When
the tubes in the amplifier warmed
up.
'l'o
eliminste this hum, the
heater of one of the 6J5GT driver
tubes (Fig. 10, Item
33; Fig. 13,
Item 33)
s
b
o
u
lc
be removed from
the
€.€
volt
w
i
nd
ing
of
�he am
power transformer
(Fig.
Item 23; Fig.
13,
Item 23)
and
connected to the 6 . 0 volt
winding of the program lighting
transformer
(
Fig.
10,
Item 2 5 ;
F i g .
lo, Item
2
5
)
.
By changing
the wiring
to
the heater
of
this
tube
(
Fig. 10, Item
33;
Fig. 13,
ltem
33)
to correspond with the
schematic diagrams (Figs.
9
and
12),
the hum during the warmup
period will be entirely elimin
ated.
E.
MICROPRONIC
TUBES
Due to the high gain and
audio output of the type 825-5
and 825-10 amplifiers, the input
6JSGT tube
10,
Item 32;
Fig. 13,
Item
occasion�lly
becomes
rn1crophon ic.
I
nter
changing this 6J5GT tube with
either of the 6J5GT driver tubes
(Fig.
10,
Item
33
or
34;
F
ig. 13,
Item 33 or 34) may eliminate
this condition, and
if
it does
not, the 6.J5GT (
F
'
ig.
lO,
Item
3
2
;
F l g .
13,
Item
32)
tube should be
replaced with
a
new tube.
I � .
PROP ER H U M B E R O F C R E l> I
TS
F A I L
TO R E G I S T E R I
H
T H E EL E C T R I CAL S E L E C T O R
A .
CREDI'l' MAGNET DOES NOT RE
SPO�D TO COIN
If
the Credit Magnet does
not respond to a coin, a check
should be made
for proper
c6n
nection of the
coin
chute to the
Solenoid Drum.
The credit mag
net ( F l g . 24, Item
17)
may also
be defective.
There may be a
2. 7
broken wire or a bad contiection.
In checking the credit circuit,
ref er to schematic diagram (Fig.
21) which shows complete circuit
and components involved.
All
plugs should be checked for
proper seating and contact points
of series relay should be ir�
spected.
Содержание 7800
Страница 40: ...c r f 1 i l r u Z i 33 I 1 1 0 0 00 00 Cl _ 0 0 i ...
Страница 44: ...CrSSI S REAR I I Ell CUTAWAY f3 I ll 37 ...
Страница 47: ... I iit L 7 8 _ 1 I I I I F I G U R E HO 6 SYM HONf ...
Страница 50: ...llll F l GURE H O 7 SYMPHOH II O I ...
Страница 57: ...CD w _ _ 0 _ i c a 0 x L I I I L i _ _ _ _ _ ____ _ _ _ _ _ _ _ _ ____ __ _ _ _ _ J 56 ...
Страница 61: ... 1 I I J I l4MlJ l ar Ii JJJ I __ I I 6 0 1m l i111 UH d uu i I f f I t I I gz d nl a s e M i ua f II Ii ...
Страница 73: ...F I G U R E H O 30 SLUG R E J E C T O R Q FRONT 72 ...
