Sencore PS163 User Manual

MEASURING THE DC LEVEL
of an AC SIGNAL
The DC level of an AC signal is often more important
than the actual signal amplitude. The DC coupled
PS163 makes the critical level measurements ac-
curately using the following procedure.
Follow the set up procedure for the Dual Trace
Methods of DC voltage measurements. In the com-
posite video waveform in Fig. 3, the DC level of the
blanking level is 2 divisions at 1 volt/Div. or 2 volts.
The DC level of the top sync pulses is 3 divisions, or
3 volts. The DC level of the negative tips of the
video information is 1 division at 1 volt per division
or 1 volt.
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Fig. 3. Measuring DC level of video signal.
COMPARISON OF VOLTAGES
In some cases, such as a stereo amplifier, a comparison
of a good working channel to the defective channel
is a quick way of establishing the defective stage or
component. The Dual Trace PS163 is an ideal in-
strument for this purpose.
1. Set the scope to AUTO TRIGGERED and press
the DUAL ALTERNATE button on the VERTICAL
INPUT switch. Use the TRACE POSITION controls
to set each trace to the same reference point on the
scope grid.
2. Use CHANNEL A on the working channel as your
reference and CHANNEL B on the defective section.
Connect both probes to the same point in each unit or
amplifier, as shown in Fig. 4.
3. Note the deflection of the CHANNEL A and the
CHANNEL Btraces. They should be the same or very
close if there is no defect at this point. When the
CHANNEL B deflection does not match the A or re-
ference channel, then the defective stage has been
located.
COMPARISON OF DC VOLTAGES
STEREO AMPLIFIER
GOOD CHANNEL
INPUT OUTPUT
— CONNECT PSI63 CHANNEL A HERE
CONNECT PS 163 CHANNEL B HERE
DEFECTIVE CHANNEL
Fig. 4. Comparing voltages in stereo amplifier.
COMPARISON of AC SIGNALS
The same technique as above can be used to observe
AC signals to locate a defective stage.
1. Use the TRACE POSITION controls to center the
CHANNEL A trace in the upper half of the 10 x 10
grid, and the CHANNEL B trace in the lower half of
the 10 x 10 grid. Use sync from CHANNEL A.
2. Connect CHANNEL A to the desired test point in
the working channel and adjust the PS163 controls
for a viewable waveform. Set the CHANNEL B PPV
PER DIV switch to the same setting and connect it to
the same test point in the other channel. The same
amplitude waveform should be observed. If a dif-
ference exists, then you have located the defective
area in the chassis.
LOCALIZATION of
INTERMITTENTS
An intermittent condition is the most difficult to
locate problem in any piece of electronic equipment.
In many cases the trouble disappears as you try to
make a measurement. The normal troubleshooting
procedure with only one scope can waste much value-
able time as you are only able to observe one test
point at a time. A dual trace oscilloscope such as the
Sencore PS163 allows you to observe two test points
at the same time, and thus cut the time that it takes
to locate the intermittent condition in half. Use the
example of Fig. 5 with the following procedure to
locate an intermittent problem in a 5 stage amplifier.
1. In the first step, connect the CHANNEL A probe
to the input of Stage 1, and the CHANNEL B probe to
the output of stage 5.
Observe the output of stage 5 and the input to stage 1
both before and after the intermittent occurs. The
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Sencore PS163 Specifications

General

Brand	Sencore
Model	PS163
Category	Test Equipment
Language	English