HP 5334B Service Manual page 185

niques, measure the AGC voltage at the junction of CR15-C13 (See Note 7 in Table 8-12, Oscillator Normal Vol-
tages). If this voltage appears normal, the problem may be a defective quartz crystal (Yl). To verify this pos-
sibility, obtain a 10 p, h (HP Part No. 9100-2265) and a 12 ph inductor (HP Part No. 9100-2242). (Use the HP
numbered parts as these have been tested in the circuit.) On the oscillator board, remove the red and blue wires
connecting the crystal to the board. Place the 12 p . h inductor in place of these wires. With 12V applied to the cir-
cuit. adjust the FREQ. ADJ. (Cl) and the amplitude control (R6) for a good sine wave signal.
At some settings of C1 andlor R6, intermittent oscillations may appear.
Some minor adjustment of C1 and/or R6 should clear this. If this fails,
replace the
12
c~h inductor with the 10 p,h inductor and repeat the C1/R6
adjustment.
8-425. If replacing the crystal with an inductor produces oscillation, this is a very good indication of a defective
crystal. When replacing crystal Y1, read paragraph 8-384(b), Special Parts Replacement Considerations. If the
circuit will still not oscillate, the problem is most likely one of the oscillator circuit elements.
8-426. OUTPUT AMPLITUDE HIGH OR LOW. Many times this can be cured by the adjustment of R6 as
described in paragraph 8-427. If the correct amplitude cannot be obtained with this adjustment, monitor the sig-
nal at Q6 collector with an oscilloscope and set R6 to obtain an amplitude of 2.8V p-p. Then check Q5 and Q9
stages. If the adjustment is not effective, investigate the operation ,of AGC circuitry (Q3, CR4, CR5, C5, CG, R5,
R6, R7, or Ql).
8-427. Output Amplitude Adjustment
8-428. The output amplitude is adjusted by the setting of the variable resistor R G which is in the feedback of
the AGC circuitry. It is not accessible from the outside of the oscillator.
8-429. The following procedure should be used to adjust the output amplitude only if the output level falls out-
side the specified level, or repairs have been made to the main oscillator or AGC circuitry.
a. Remove oscillator from instrument.
b. Remove the three screws holding the bottom cover on the oscillator. Remove the bottom cover and
allow the oscillator to cool (if previously operated).
c. Remove the two screws securing the P.C. edge connector to the outer can. Remove the top foam in-
sulator to expose the oscillator circuits.
HP 5334B
-
Service Manual
8-65