HP 5334B Service Manual page 165

8-323. If the high frequency signal is not getting through, trace the signal through the circuit and check the com-
ponent that
is
not passing the signal. Remember to use a 10 MQ probe at the gate of FET Q8.
Measure approximately 280 millivolts p-p with
+
0.22 volt dc offset at the gate of Q8.
8-324. To check the LOW FREQUENCY path set the equipment as follows:
53348 Signal Source
1
kHz, 1 Volt p-p sine wave
(set HP 3325A to
5V
to generate
1V
p-p signal)
0 volt, dc offset
50Q
....................................................
ON
AUTO TRIG
...................................
OFF
a. Apply the 1 kHz
signal to the Channel A Input.
b. Adjust the TRIGGER LEVEWSENS control for a 0 volt dc level at the emitter of Q10.
c. Measure approximately 350 millivolts p-p at the emitter of Q10.
8-325. Should the low frequency output be incorrect, trace the signal through the low frequency path to find
the faulty component. Remember that signal measurements at the input to U30 should be taken with a 10
megohm probe to ensure an accurate reading.
a. Measurement approximately 140 millivolts p-p with no dc offset at the inputs of U30 (pins 2 and 3).
b. Measure approximately 10 millivolts p-p with a
-
1.7 volt dc offset at the output of U30 (pin 6).
8-326. If the 5334B miscounts, or displays a reading without a signal being applied to it, the problem may be
due to self-oscillation in the low frequency circuit. With no input into the Counter, probe the collector of Q6. If
a signal is present, changing operational amplifier U30 may clear up the problem.
8-327. To check the Trigger Level function:
Settings of the 5334B
AUTO TRIG
...................................
OFF
a. Remove any.input signal to the Counter.
b. Measure + 4 to
-
4 volts at the emitter of Q10 as the front panel TRIGGER LEVELISENS control
is varied over its full range.
8-328. If the voltage at QlO is incorrect:
a. Check that the voltage at the collector of Q6 has the proper range ( + 4 volts).
b. Check the inputs to the operational amplifier, U30, at pins 2 and 3. Both inputs should stay at 0-volt
dc regardless of the front panel TRIGGER LEVEL control setting.
8-329. If the voltage at the collector of Q6 is wrong:
a. Check the voltage from the TRIGGER LEVEL at the junction of resistors R112 and R l l l near the
input of U30. Measure -2.5 to +2.5 volts as the TRIGGER LEVEL is adjusted.
b. This voltage passes through switching circuitry in the DAC block on its way to the operational
amplifier, so the TRIGGER LEVEL control or the DAC block may be at fault.
HP 5334B
-
Service Manual
8-45