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HP 437B
Service Sheet BD1
1 ms/DIV
Figure 8-8. A4TP5 Phase Detector Waveform
Service Sheet A4b Troubleshooting
16.
17.
18.
8-36
SERVICE
Select a digital filter setting of 1 for the Power Meter.
This selects the
fast low-pass filter.
Connect the oscilloscope to A4TP7.
Verify that the dc voltage at A4TP7 is approximately equal to the peak
@
voltage at A4TP5 (see Step 9).
Select a digital filter setting of 512 for the Power Meter. This selects
the slow low-pass filter.
Verify that the dc voltage at A4TP7 is approximately equal to the peak
voltage at A4TP5 (see Step !0).
Verify that the dc voltage from the AUTO-ZERO
DAC at the junction
of R57 and C26 (see Figure 8-9) is between +15 mV.
Figure 8-9. R57-C26 Junction Location
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