HP 5334B Service Manual page 167

8-336. If the Schrnitt outputs are missing or incorrect:
a. Verify that the correct input is present before replacing U22. If only one of the two ECL outputs is in-
correct, check the resistor pack, R37, for opens or shorts before replacing U22.
8-337. The Comparator Offset adjustment (AVOS, R58) can be checked using the same setup as in the pre-
vious tests:
a. Note the present voltage at U22A pin 8. This voltage is needed so that the offset can be returned to
its original value.
b. Vary the Channel A voltage offset resistor (AVOS, R58) over its f u l l range. The voltage at pin 8
should vary from
+
20 to - 20 millivolts.
c. If this voltage is incorrect, check the
+
5 and
-
5.2 supply voltages at R58. Also check the divider
resistors R56 and R57 as well as R58 for opens or shorts.
d. Remember to reset the voltage at pin 8 to its original value after making this check.
8-338. If the SENS control does not work when the Counter is in the Sensitivity mode:
a. Check the LATCH ENABLE l i e at pin 4 of U22A. The voltage should vary from approximately
+50 to -50 millivolts as the SENS control is adjusted over its f u l l range. If these voltages are incor-
rect, check the SENS control or the DAC block switching circuitry. If the voltage has the correct
range, U22 may be defective.
8-339. In the last part of the Channel A circuit, the BUFFER STAGE, a problem can be partially isolated by
observing the failure symptoms of the Counter. During a measurement, the display may be incorrect or missing,
or the front panel trigger light may fail to flash. If only one of these failures occur, the fault is probably in the
buffer stage. Replacing U21 may f u r the problem. However, if both of these symptoms occur together, verify the
output of the previous Schmitt stage before troubleshooting the buffer stage.
8-340. To check the Buffer Stage:
Settings of 5334B
Settings of Signal Source
FREQ A
.......................................
ON 1
MHz, 1 Volt p-p sine wave
(set HP3325A AMPTD to
.5V
to generate a 1V p-p signal)
0 volt, dc offset
50R
....................................................
ON
AUTO TRIG
...................................
OFF
SENS
.................................................
ON
SENS control
.................................
Fully CW
a. Apply the signal to the Channel
A
Input and note the failure symptoms.
b. A display problem is caused by the Level-Shifter, U21C which provides the input to the Multiple-
Register Counter (MRC).
A
defective Trigger Light function is caused by the Trigger Light One-
Shot, U21B.
c. Measure the output of the level-shifter U21C, at pin 12. If the
1
MHz, TTL signd is missing or incor-
rect, verify the input to the level-shifter at pins 10 and 11.
d. If the complementary ECL signals are not present, check the damping and pull-down resistor packs,
R36 and R37, for opens or shorts. Verify that the output of the Schmitt Stage is correct.
HP 5334B
-
Service Manual
8-47