HP 5334B Service Manual page 166

8-330. If the Q6 collector voltage lacks the proper range, check the gain resistors (R95, R96, R110, and R111)
before replacing any active components. An open, or shorted, resistor may be the problem. This could cause the
voltage at the collector of Q6 to be nonvariable.
8-331. If the Q6 collector voltage is stuck at -5 volts, Q6 is probably shorted. If the voltage is stuck at 0-volt,
the probable cause is a shorted base-to-emitter junction in the emitter-follower, Q10.
8-332. If Q6 collector voltage is stuck at greater than
+
4 volts:
Check the voltage across the base-to-emitter junction of Q6. If the correct voltage drop of 0.7 volts is measured,
Q6 may be open or not turning ON, or Q8 or Q10 may be shorted out.
8-333. If the Q6 base-to-emitter voltage is not correct:
a. Check Q6 base drive resistor R79 and stabilizing resistor R61 for opens or shorts.
b. Also check filtering capacitor C58 for a possible short. If these components appear to be good, either
Q6 or U30 may be defective.
8-334. The next section of the Channel A circuit, the SCHMITT STAGE, has only one active component, com-
parator U22. In most cases, replacing U22 will clear up a failure in this stage.
NOTE
When signal tracing in this circuit, the ECL signals at the output of U22 will
show some ringing unless a short ground lead is used on the oscilloscope
probe.
8-335. If the SCHMITT STAGE is suspected of failing, set the equipment as follows:
5334B
Signal Source
FREQ A
...........................................
ON 1
MHz,
1
Volt p-p sine wave
(set HP 3325A AMPTD to 3 to generate a 1V p-p signal)
0 volt, dc offset
50i2
....................................................
ON
SENS
.................................................
ON
SENS control
.................................
Fully CW
a. Apply the signal to the Channel A Input.
b. Measure the signal amplitude before and after the divider circuit (R55 and R75) at the input of
U22A. Measure the signal at the emitter of Q10 where it should equal 350 millivolts p-p and at U22A
input pin 7 where it should equal approximately 250 millivolts.
c. If this amplitude is incorrect, check the divider circuit components R55, R75, and C70.
d. Next measure the complementary ECL outputs of the U22A comparator at pins
1
and 2. Observe a
+
1V p-p square wave signal with a
-
1.25V dc offset. Any ringing on the signal is probably caused
by the length of the ground lead on the oscilloscope probe.
HP 5334B - Service
Manual
8-46