Emerson Keystone Figure 637, Service Manual

Page: 10 / 37

Emerson Radio
of retrace of horizontal scanning, the field built
up in the .primary collapses and induces a high-
voltage. This voltage is applied to the high-voltage
rectifier (V 1 8 ). From 8.5 to 10 kilovolts is pro­
duced by the power supply. The rectified voltage
is filtered by C63 and R89, and applied to the
second anode of the kinescope. Chassis 120113B
differs from Chassis 1201 IB in that C63 is return­
ed to B— , instead of the plate of V I 9.
b. L O W V O L T A G E S U P P L Y : The low-voltage
supply uses a full-wave rectifier (V 29) and trans­
former (T 1 2 ). A series arrangement is used to
supply plate voltage, to reduce current require­
ments.
As a result, separate filament windings
are used to keep the heater-cathode potentials
within ratings, and the electrolytic filter conden­
sers are not grounded to the chassis. The center-
tap of T12 is not grounded but is negative (B — )
with respect to ground. The cathodes of the sweep
circuit and video amplifier tubes are negative to
ground (about -205 volts) and the heaters are
conected to the ungrounded filament winding ( Y ) .
6. INTERCARRIER SOUND— The audio circuits
are conventional. The 4.5 me. heterodyne between the
video and audio i-f carriers is taken from the shunt-
tuned circuit (L2, C79) at the output of the video de­
tector (V 4 ). The 4.5 me. signal is amplified by the
audio i-f amplifier (V 7 ), whose output is coupled to
the limiter (V 8 ). V8 feeds the discriminator (V 9 A ) ;
the output of the discriminator is amplified by V93,
ana tne audio output (V 1 0 ).
7. DEFLECTION YOKE AND FOCUS COIL
ASSEMBLY: The deflection yoke and focus coil
form a complete assembly. The yoke contains the
vertical and horizontal deflection coils (L 8 and
L 9 ). The focus coil (L 10) combines a permanent
magnet with the electromagnet (P M and E M ).
The yoke and focus coil are independently ad­
justable.
Vertical centering is accomplished by mechani­
cal adjustment of the focus coil; horizontal center­
ing is done electrically by the H OR. C E N TER­
ING control (R 103). Later production of Chas­
sis 12011 OB and 120113B makes use of a pivoted
mounting for the EM-PM focus coil, together
with a “ wobble plate” to provide for mechanical
adjustment of horizontal and vertical centering.
The “ wobble plate” consists of a ring of perme­
able material (steel) surrounding the neck of the
kinescope, adjacent to the EM -PM focus coil.
The plate may be moved in a plane at right-angles
to the axis of the kinescope, both vertically and
horizontally, by means of a slotted section and
lever. In addition, the focus coil may be tilted in
bqth directions by means of a second lever which
is adjustable from the rear of the cabinet, without
removing the back. This enables precise mechani­
cal control of centering.
Section
5.
MAINTENANCE A N D ALIGNMENT
1. GENERAL— All adjustments must be made only
by qualified service technicians. Unsatisfactory oper­
ation should be analyzed and circuits checked syste­
matically to locate and correct sources of trouble.
WARNING
High voltages in excess of -8000 volts are present
in the chassis, during operation. Exercise care in
servicing the receiver, when energized.
Do not
remove, handle, or replace the kinescope unless
gloves and goggles are worn.
2. CHASSIS REMOVAL— To remove the chassis,
follow the outlined procedure.
a.
Pry off all control knobs.
b> Remove the six screws which fasten the back in
place.
c. Remove the speaker plug.
d. Remove the four chassis bolts and carefully slide
the chassis from the cabinet. When inverting the
chassis, place a supporting block under the power
transformer.
3. KINESCOPE REPLACEMENT —
CAUTION
Before removing the kinescope, discharge the tube
by connecting an insulated test prod to the chassis
and to the high-voltage anode. Wear gloves and
goggles before handling the tube.
To remove the tube, proceed as follows:
a. Disconnect the high-voltage lead at the top of the
kinescope and discharge the tube.
b. Remove the enclosure which protects the base of
the kinescope.
c. Remove, the tube socket and slide off the ion trap.
d. Loosen the hold-down strap at the front of the
tube and carefully withdraw the kinescope for­
ward from the deflection yoke and focus coil as­
sembly.
To install a new kinescope, follow the above pro­
cedure in reverse. Make certain that the tube is
seated against the edges of the deflection yoke
assembly, with the high-voltage anode connection
at the top. In replacing the ion trap, position the
unit so that the arrow points towards the front of
the chassis.
NOTE
Whenever the kinescope is removed or replaced,
the mask should be carefully cleaned with a soft,
lintless cloth. Do not use carbon tetrachloride or
any cleanser containing abrasive material.
The
face of the kinescope should also be wiped clean,
before replacing the chassis in the cabinet.
4. MECHANICAL DEFLECTION A D J U S T ­
MENTS — See figure 5-1. Replacement of the kine­
scope or of any of the components of the deflection
system will require readjustment o f the deflection yoke
assembly, focus coil, and ion trap.
NOTE
Before making any deflection adjustments, make
certain that the enclosure is in place, covering
the base of the kinescope, and is firmly fastened.
The adjustments to the focus coil can be made
through openings provided in the enclosure.
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Scanned by mbear2k - Jan 20121/17