HP 85027A/B/C Service
SECTION 8
SERVICE
INTRODUCTION
You will find in this section information concerning troubleshooting and repair of the
HP 85027. Heed the caution signs or risk damaging the bridge. You may wish to read
the Theory of Operation with its associated diagrams as an aid to troubleshooting.
Troubleshooting the bridge begins with performing the Operator’s Check (Section 3) and
the Performance Tests (Section 4). If the bridge does not pass the Performance Tests,
refer to Adjustments in Section 5. If the problem persists, refer to Troubleshooting
Procedures later in this section. Those procedures require the use of test equipment
which is listed in Section 1, General Information.
You will also find the following inspection, repair and replacement procedures in this
section:
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Gaining Internal Access
*
Cable Continuity Check
Power Cable Replacement
*
Input Port and Test Port Resistance Checks
*
A2 Circuit Board Assembly Replacement
*
Microcircuit Check
Al Bridge Microcircuit Assembly Replacement
*
Power Supply Check
*
Signal Path Check
*
Clock/Control Check
*
Connector Inspection
*
HP 85027A APC-7 Connector Repair
THEORY OF OPERATION
The HP 85027 can detect RF or microwave signals which are either 27.8 kHz
squarewave modulated (AC mode) or unmodulated (DC mode). In both detection
modes, the bridge provides a 27.8 kHz square wave signal for the analyzer to interpret
and display.
In AC mode, the signal is amplitude modulated at the source. The bridge demodulates
(envelop detects) this signal to produce a 27.8 kHz square wave signal whose
peak-to-peak voltage corresponds to the magnitude of the signal at the bridge test port.
Since only the modulated signal is detected, unmodulated broadband noise and
extraneous signals are disregarded. Additionally, this technique provides nearly
drift-free operation
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