Receiver Troubleshooting - HP 3456A Operating And Service Manual

Model 3456A
c
.2V
.2V
.2V
Figure B·A·9. Input to
. 8-A-42. Incorrect Number
Wavdorm. With
waveform at the core of T I .
a . I f all the Low Pulses are missing, check the
waveform shown in Figure 8-A-98 at pin 2 of U19. If
the waveform is good, replace U19. I f not, replace UI5
or U19.
b. If all the High Pulses are missing, check the
waveform shown in Figure 8-A-9C at pin ID of U19. If
the waveform is good, replace U19. If bad, replace UI5
or U19.
c. If more than 9 pulses are on the waveform at the
core of TI, use a logic probe and make sure that pin 2 of
U6 toggles. If pin 2 toggles, replace U I . If not, replace
U6.
d. If fewer than 9 pulses are on the waveform at the
core o f T l , replace U I . (Note: Make sure the failure in
Step a and b is not present, before replacing U \.)
8-A-43. Incorrect Combination of Pulses.
probe, check for toggling at pin 2 of U6. If pin 2 is not
toggling, replace U6. If the pin toggles, replace UID.
8-A-44. Incorrect Wavdorm.
incorrect timing caused by U6b and c, U2b and c, and
5 "sec. Pos. Trig.
B
Pos. Trig.
5 "sec.
5 "sec. Neg. Trig.
un.
or Pulses on the
an oscilloscope, observe
With a logic
This may be because of
Ul7a. Check for Input/Output shorts on U2 and U6. If
a short is noted, replace the defective
are noted, replace U 1 7 .
Make sure the f ailure is not an Incorrecl
Number o f Pulses, before troubleshooting
for an Incorrect Wavef orm.
8-A-4S. Receiver Troubleshooting.
8-A-46. Troubleshooting the Receiver can be done by
using the following Signal Tracing Technique:
a. With an oscilloscope, check for the waveform
shown in Figure 8-A-1D at the core of A3T2. I f the
waveform is not present, replace T2.
.2V
Figure 8-A-10. Receiver Inputs.
b. Measure for the waveform shown in Figure
8-A- I t A at the junction of RI7 and R21 (Figure
8-A- I I B shows the expanded waveform).
waveform is not present, replace T2 .
the
.2V
Figure
c. Measure for the waveform shown in Figure
8-A-12A at pin 6 of U21. (Figure 8-A-12B shows the ex-
le.
If no shorts
NOTE
5 l'sec. Pos. Trig.
A
5 "sec. Pos. Tr1g.
2 l'sec.
Pos. Trig.
Output of 12.
B-A- t t .
Service
I f the
8-A-19