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HP 85027A/B/C Service
In DC mode, the source signal is not modulated. Instead the bridge converts the signal
into an equivalent DC voltage which it then chops at a frequency of 27.8 kHz. Finally
it amplifies the chopped signal to simulate the signal produced by AC detection and
outputs this signal to the analyzer. This technique is preferrable for devices such as
some amplifiers with ALC circuits and very narrow bandwidth filters.
TROUBLESHOOTING PROCEDURES
If a problem persists after you have performed the Operator's Check in Section 3 or the
Performance Tests in Section 4, perform the troubleshooting procedures outlined below.
CAUTION
The HP 85027 contains microcircuits which are highly
sensitive to electrostatic discharge (ESD). Work only at a
station equipped with an anti-static surface. Wear a grounded
wrist strap. Do not touch the center contacts of the connectors
with your fingers. Before you make a measurement, ground
the leads of the digital multimeter by touching them to the
grounded instrument chassis.
Gaining Internal Access
To obtain access to the interior of the HP 85027, proceed as follows:
1.
Disconnect the bridge from the analyzer.
2.
With the HP 85027A only, use a thin 1/2 inch open-end wrench to remove the
coupling nut from the APC-7 test port connector.
3.
Remove the two screws which hold the (test) port cover (end plate).
4.
Remove the port cover.
5.
Slide the top dress cover out of the bridge housing. The component side of the
circuit board and the bridge assembly are now accessible.
Cable Continuity Check
1.
Disconnect the HP 85027 from the analyzer and ground the leads of the DMM by
touching them to the grounded chassis of the DMM.
2.
Use a digital multimeter (DMM) to check the continuity of the conductors of the
power cable (Wl) from the connector pins to the wire connections inside the
bridge housing. Table 8-1 lists the Wl connector pins and the corresponding wires.
3.
If there are any discontinuities , replace cable Wl by following the instructions in
Power Cable Replacement.
8-2
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