Sencore PS163 User Manual

even the newer I. C. demodulator. You are no longer
imited to just viewing a vector pattern at the output
of the difference amplifiers.
Fig. 15. Vector pattern showing weak blue signal.
Incorrect Phase Angle: The phase angle between the
R-Y and B-Y signal is from 90 to 120 degrees, depend-
ing upon the receiver and the manufacturer. This
angle is adjustable in most of the older receivers and is
fixed in the newer sets. To set the phase angle,
connect the scope and obtain a vector pattern as pre-
viously described.
Set the third or R-Y bar to its proper position and
note the position of the sixth or B-Y petal. It should
fall between the B-Y mark (90°) and the number 7
(120°) on the vector graticule. Adjust the demod-
ulator phase transformer to position the B-Y petal on
its correct mark. The R-Y petal will move slightly. It
should be repositioned with the tint control to its
proper mark and the position of the B-Y petal re-
checked.
Most of the newer receivers have fixed components
and do not require adjustment. If one of these fixed
components is replaced, the angle should be checked
to be sure that you are on or close to the proper angle.
An off value part can shift the angle so it is difficult
for your customer to obtain flesh tones.
Total loss of Color: A total loss of color will result in
no pattern except the blanking as shown in Fig. 16.
The color oscillator, color killer, bandpass amplifier or
demodulator could be at fault. Convert the PS163
from a vector scope back to a single or dual trace
scope by pressing one of the other VERTICAL IN-
PUT buttons and use normal troubleshooting proced-
ures to locate the defective stage.
Fig. 16. Vector pattern obtained with no color
output.
Solid State Chroma Amplifiers: In many of the newer
receivers transistors are being used to drive the picture
tube. The signal level is still quite high at this point,
but the cathodes are being driven and not the con-
trol grids as was done with tube receivers. The probes
must be connected to the cathodes of the CRT to ob-
tain a vector pattern on these receivers. This will give
an upside down and backwards looking pattern. This is
normal. The important points about the vector pat-
tern still remain the same. Use the 9 on the vector
grid as the R-Y mark, the BURST as the B-Y mark,
and the B-Y as the burst mark. It will also be nec-
essary to shunt the video information to ground to ob-
tain a clean vector pattern. To do this, temporarily
connect a 20mfd electrolytic capacitor from the base
of the video amp to ground.
SQUARE WAVE TESTING
WITH THE PS163
Square wave testing of audio and video amplifier is
astandard procedure with many advanced technicians.
The response of the amplifier as well as many circuit
troubles are easily determined by the shape and dis-
tortion present in the square wave. Loss of high fre-
quency response, phase shift, poor low frequency
response and ringing are a few of the problems that
can be found with this method.
21

Sencore PS163 Specifications

General

Brand	Sencore
Model	PS163
Category	Test Equipment
Language	English