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HP 85027A/B/C Service
2.
Set the RF output to +13 dBm with the modulation on.
3.
With a true RMS DMM, measure the voltage across the two output pins of the
microcircuit.
4.
The bridge diode is probably good if the reading in step 3 is approximately
0.07Vrms.
5.
If the reading in step 3 is low, remove the self-adhesive plastic label with the note
which explains the switch configuration and center the load potentiometer (R29,
see Figure 5-2). Measure again. If the reading remains low, the microcircuit is
defective and must be replaced.
A 2 Circuit Board Assembly Replacement
1.
To remove the circuit board, first open up the bridge and unsolder the power
cable wires (see "Gaining Internal Access" and "Power Cable Replacement").
2.
At the circuit board pads, unsolder the signal, signal ground and chassis ground
wires from the microcircuit.
3.
Remove the four screws and lock washers which fasten the A2 circuit board to the
standoffs.
4.
Reverse the above procedure to install the repaired or replacement board.
5.
Refer to Section 5, Adjustments, and perform them as indicated to match the A2
board to the A1 microcircuit.
6.
Reassembly the remaining parts of the bridge.
A1
Bridge Microcircuit Assembly Replacement
1.
Type the serial number of the HP 85027 on the rear panel label supplied with the
new or replacement bridge assembly.
2.
On the HP 85027A only, remove the coupling nut from the APC-7 test port
connector with a thin 1/2 inch open-end wrench.
3.
Remove the two screws holding the (test) port cover (end plate) and remove the
port cover.
4.
Remove the two screws holding the cable cover (end plate). This will allow the
cable and cable cover to move freely.
5.
Unsolder the two white/black wires (signal ground and chassis ground) and the
white/red wire (signal) at the microcircuit. Remove the capacitor from the
microcircuit pins.
6.
Remove the four screws and lockwashers which fasten the A2 Circuit Board
Assembly to the standoffs.
7.
Remove the A2 Circuit Board Assembly with the cable cover and cable from the
extruded housing.
8-4
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