Part 2. Troubleshooting; 4.6 General; Part 3. Alignment And Calibration; Null Indicator Alignment - Boonton 75D Instruction Manual

Direct capacitance bridge

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PART II.

TROUBLESHOOTING

4.6 GENERAL.

The troubleshooting chart in Table 6 lists faults in descending

order of probability.

This order of probability should be followed unless inspection

reveals an obvious defect, such as a charred part, a broken lead, or arcing discoloration.

Use the troubleshooting chart as a guide to locate a fault in one of the main assemblies

in the Model 75D and then to isolate a fault to a stage or circuit. Most faults then can

be isolated by performing voltage and resistance (V & R) measurements in accordance

with Figure II, When troubleshooting a stage or circuit, also check associated wiring

and any interconnecting cabling.

Use the schematic diagram to trace circuits and to

obtain values of component parts.

If a fault is located in the oscillator-detector

assembly, use Figurel4as a supplementary diagnostic aid.

During troubleshooting refer

to Figuresl2through 13 and the schematic as applicable, for locations of parts and

internal controls.

When troubleshooting and repairs are completed, perform the entire

procedure in the equipment performance checklist (Table 5) as a final test.

NOTE:

If a fault or malfunction appears to be in the bridge assembly,

call on the Boonton Electronics Corporation or your nearest

sales engineering representative.

The Model 75D warranty will

be null and void if the seals on the bridge assembly are broken or

removed without authorization.

PART III.

ALIGNMENT AND CALIBRATION

4.7

GENERAL. When alignment or calibration is required, perform only the

alignment or calibration procedures called for in the troubleshooting chart (Table 6).

Each alignment or calibration procedure lists the required test equipment and contains

applicable disassembly and reassembly references. When more than one procedure is to

be performed, reassemble the Model 75D after the last procedure is completed.

Figures

1 2 and 13

indicate the internal controls used for alignment or calibration.

4.8

NULL INDICATOR ALIGNMENT (R307).

(1)

Test equipment:

None.

(2)

Procedure:

Remove the Model 75D cabinet (par. 4.12).

Adjust the Model 75D front panel controls in accordance with Table 4.

Turn the GAIN control fully counterclockwise (ccw).

Remove tube V203.

Adjust R307 until the NULL INDICATOR pointer is directly over the

extreme left increment (zero) in the LO sector of the meter scale.

75D

b-370

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