RCA Victor TRK-12, Manual

Page: 13 / 29

PAGE 2 6 5 - C
TRK9, TRK90, TRKI2, TRKI20
Figure 12— Partial Video Chassis W iring T R K -9 and T R K -1 2 W ith P icture A V C . Otherwise same as Figure 13.
Television Service Suggestions
the 5V4-G dam per tube can be replaced by a 5Z4. This may
cause a slight spreading of the picture on the left-hand side.
16. Picture compressed on left-hand side. Shrinking of
the picture on the left-hand side may be caused by a defec-
tive 6L6 horizontal o utput tube. Also check 6L6 cathode
resistor.
17. Inability to center picture. This may. be due to low
voltage across the centering control caused by a defective
low-voltage rectifier or low line voltage. A nother possibility
is th a t the elements in the Kinescope may be tilted. This can
be checked as follows:
W ith the brightness control at normal setting, turn the
receiver on and observe the position of the illuminated spot
during the few seconds before the horizontal and vertical de­
flection voltages start operating. T h e illuminated spot should
be in the center of the Kinescope (its position during these
few seconds is not affected by the centering controls). If the
spot is off center, it is a definite indication th at the Kinescope
“ gun” is tilted.
18. D istorted sound or sound in picture. A n open in one
side of the antenna transmission line can cause distorted
sound. O th e r possibilities include:
(a ) If the sound-IF response curve is n o t linear fo r 75
kilocycles on each side of 8.25 me., distortion will result.
(b ) Inaccurate adjustm ent of the oscillator frequency bn
any channel may result in no sound o r distorted sound, due
to the fact th at the sound-IF beat frequency will no t be 8.25
me. If the oscillator frequency is too low, the beat note, in­
stead of falling on the high-frequency slope of the sound-IF
response curve, may fall on the low-trequency slope. In this
case, the sound may be satisfactory, b u t operation on this
side of the curve should be avoided. In some localities, it
results in sound image interference from other channels.
A quick and definite method to check the oscillator fre­
quency is as follows:
(a ) T une in a television station.
(b ) .T urn the fine-tuning trim m er to minimum capacity.
This should prpduce some evidence of sound in the picture.
T h e sound usually appears as horizontal bars o f . varying
density, and these vary in step with the speech o r music. T he
bars disappear when the voice o r music stops.
(Continued)
(c ) T urn the trim m er for best sound quality. This should
correspond to approximately half-capacity of tnie trimmer.
(d ) T u rn the trimmer toward maximum capacity. If the
slope of the sound-IF response curve is narrow, this will move
the beat on to the_ peak of the response curve, producing
low volume and severe distortion.
O n service work in the home o r where test equipm ent is
not available, if one or more of the oscillator frequencies re­
quire re-adjustment, the recommended procedure is as
follows:
(a) T une in the television station on the channel which re­
quires re-adjustment of the oscillator frequency.
(b ) T u rn the fine-tuning trim m er to minimum capacity.
(c ) T u rn the magnedte-ebre for the particular oscillator
coil toward the highest frequency position (core moved away
from the coil). This will definitely p u t sound in the picture.
T urn the core in the opposite direction, to lower the oscil­
lator frequency, until the sound is barely perceptible in the
picture. Leave the core in this position.
(d ) Now, by turning the fine-tuning trim m er to half-
capacity, it should be possible to secure good tone quality
with no trace of* sound in the picture.
If the sound-IF is deliberately moved into the picture-IF
by adjusting the oscillator core to produce the highest fre­
quency, the effect of the sound-IF interference will produce
a “ reversed" image, somewhat like a film negative.
T h e customer should be instructed to adjust the fine-tuning
control for-best sound quality, a t which point there is no
sound in the picture. If the set is turned on in a cold room,
it may be necessary for the customer to readjust the fine-
tuning trim m er to compensate for the slight' d rift in oscillator
frequency during the warm-up period.
O n all converted receivers, the fine-tuning trim m er is per­
manently fastened to the fine-tuning control, so th a t it is not
necessary to press in on the control knob. ( “C " washers are-
slipped between the end of th e shaft and the rubber drive
and cement is used between the rubber drive cone and the
cup on the fine-tuning trimmer.)
19. Insufficient sound. In locations remote from the trans­
mitter, additional sound volume can be obtained in the 9-inch
and 12-inch receivers by eliminating the irtverse feedback in
the audio 'amplifier of the radio chassis.
( Continued )