11-3 11-3
Measuring point
C:
The first stage of the modulator is an integrator. An integra-
ted rectangle results in a triangle.
Measuring point
D:
The oscillator signal (squarewave) is fed to the second inte-
grator (7122-B).
Measuring point
E:
The integrated rectangle results in a triangle. 7122-C works
as a comparator. 7122-D improves the shape of the pulses.
Measuring point
F: Output modulator
In this pulse width modulated square wave the analog
Audio signal is included. Measurements with an analog
scope will show a jitter on the falling edge.
The modulator frequency is still fixed to 500kHz. Similar to a
frequency modulation - in this case the amplitude of the
analog audio signal varies the pulse width, the frequency
defines the speed.
Measuring point
G:
The low-side driver signal <G1> (Ch2) is the modulator out-
put level-shifted by transistor 7128. The high-side driver sig-
nal <G2> (Ch1) is the inverted low-side driver signal level-
shifted by transistor 7119.
Service Hints
Measuring point H: gate-signal of the FETs
Ch1 = H1, CH2 = H2
Measuring point
I:
Digital output signal.
Measuring point
J:
The following three signals are measured after output filter
5101 with different timebases.
Measuring point K:
After common mode coil 5102 - the audio signal is restored.
Service Hints
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