Oscillator Section Normal Voltages - HP 5334B Service Manual

8-414. OPTION 010 OSCILLATOR CIRCUIT TROUBLESHOOTING
8-415. The oscillator circuits are relatively simple and straightforward. The following paragraphs will briefly
describe the major circuit areas, a troubleshooting outline, and some helpful suggestions to make the
troubleshooting process easier. The oscillator consists of four sections, listed below:
a. Oscillator Q1, Q2, and associated circuitry.
b. AGC Q3, CR4, CR5, and R6.
c. Output circuit Q5 and Q9.
d. 5.W power supply CR2, CR3, and Q4.
The oscillator is the signal source. Its output level is controlled by the AGC. The 5.7V power supply provides an
extra-stable clean voltage source for the oscillator circuits. The output circuits provide a high-level signal capable
of driving a 50n
to 1KSZ load.
8-41 6. Normal Operation
8-417. The output of the oscillator circuit at Q2 collector is a 10 MHz undistorted sine wave with an amplitude
of approximately 2.8V p-p. The AGC voltage (measured at CR5-C13 junction) is approximately
-
1.5V. The
10 MHz signal passes through Q5 to Q9 base at about the same level. The voltage gain of amplifier Q5 (base to
collector) is approximately 2 with a 50a load on the output. The output of transformer T1 is approximately
1.5V p-p. All 10 MHz signals found in the oscillator will be undistorted sine waves unless otherwise noted in
Table 8-12, Oscillator Section Normal Voltages.
8-41 8. Troubleshooting
8-419. When troubleshooting the oscillator section, remove the oven mass from the housing and the covers
from the oven mass as described in paragraph 8-397. Connect 12V to the oscillator section; use the special con-
nector described in paragraph 8-386, Special Test Connector. Set the power supply current limit to 60 mA. DO
NOT apply power to the oven circuits!
8-420. Initial troubleshooting and probing should be done on the backside of the boards (trace side) while they
are secured to the oven mass (see paragraph 8-398, step h). This way the circuits are more easily handled. When
the fault is isolated to a few components, the unit may then be disassembled for final troubleshooting and repair.
8-421. Helpful Hints
a. Most points in the oscillator circuits cannot be measured with a dc voltmeter. The reactance of the
voltmeter probe and leads will load the circuit and give false readings. Instead, use an oscilloscope
with a high input impedance probe for these measurements. Table 8-12, Oscillator Section Normal
Voltages, indicates when a dc voltmeter can be used.
b. Before reinstalling the oven mass into the housing, adjust the output amplitude as instructed in
paragraph 8-427, Output Amplitude Adjustment.
8-422. Symptoms of failures in the oscillator sections will generally fall into one of the following categories:
a. No output.
b. Output Amplitude is low or high.
c. Excessive drift of output frequency.
HP 5334B
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Service Manual
8-63