Digital-To-Analog Converter (Dac) Troubleshooting - HP 5334B Service Manual

8-341. If the Level-Shifter is operating correctly:
a.
Measure the input to the MRC, UU) of the ExecutiveMeasurement Block. The
1
MHz signal at pin
30 of U20 should be an ECL signal of 0.8 Volts p-p riding on a dc level of approximately
+
2.7 volts.
b. If the signal is missing or is a TTL signal, check the voltage divider components R51, R52, and C54
for opens or shorts. Also check the dc level adjustment divider, R128 and R130.
8-342. The Trigger Light One-Shot circuit should cause the front panel trigger light to flash at a 10 Hz rate,
when using the same setup and input as before. If the trigger light is dead:
a. Check the output of the one-shot, U21B. The signal at pin 5 should be a 10 Hz TTL signal. If this out-
put is good, the signal may not be reaching the front panel.
b. Trace the signal through the inverter U24E, the current-limiting resistor pack (R118) and finally, to
the front panel LED (DS61).
8-343. If the one-shot output is dead:
a. Measure the input at U21B pin 6 and verify the presence of the 1 MHz, ECL signal of
+
1
volt p-p
offset by
-
1.3 volts dc. Troubelshoot the Schmitt Stage if this signal is missing.
b. If the input is good, disconnect the
1 MHz input to the Counter and measure the dc reference at
U21B, pin 7. It should be approximately
-
1.3 volts. If this voltage is incorrect, check the Vbb
reference voltage at pin
1
for an approximate level of
-
1.3 volts. Also check resistor R53 and
capacitor C45 on the reference voltage line for opens or shorts.
8-344. A trigger light failure may be caused by a defective feedback loop. To check for this:
Settings of 5334B
AUTO TRIG
...................................
OFF
SENS
.................................................
OFF
No Input Signal to the Counter.
a.
Vary the TRIGGER LEVEL control over its range and note whether the Trigger Light turns ON
and OFF. If the one-shot
will
not operate manually, replace U21.
b. If the Trigger Light works correctly in the manual mode, but will not flash at approximately 10 Hz
rate during a measurement, then the feedback loop is defective. Check the feedback components R54
and C47 for opens or shorts.
8-345. DIGITAL-TO-ANALOG CONVERTER (DAC) TROUBLESHOOTING
8-346. Failure symptoms in the DAC block include not being able to perform the DAC Zero or DAC Gain Ad-
justments, and a defective READ LEVELS-Trigger Levels or READ LEVELS-Peak Levels display. There are
no Failure Messages which apply specifically to the DAC block. However, a defective DAC Integrated Circuit
may cause a failure message display related to the Measurement Data Bus.
HP 5334B
-
Service
Manual
8-48