28. Attenuator Rpp Troubleshooting 6D-21 - Fluke 6080A Service Manual

ATTENUATOR/RPP TROUBLESHOOTING
Attenuator problems are most likely to be relay contact problems.
Connect the power meter to the UUT RF OUT connector and check the nominal levels
at 100 kHz and 1056 MHz per Table 6D-5 to isolate a faulty attenuator section.
Table 6D-6 can be used to verify proper control of the attenuator sections versus the
programmed UUT level. Errors here could indicate a problem with the Controller
PCA or the Relay Driver PCA (Q1 through Q7 and associated circuitry).
A through path problem on the Attenuator/RPP PCA may be difficult to isolate. First
verify the Output PCA signal. See paragraph 6D-8. If there is an apparent through
path problem but one of the observed levels from Table 6D-5 is correct, that associated
relay may be at fault. Another method to isolate a bad relay is to remove the
Attenuator/RPP assembly from the module leaving the control/power ribbon cable
attached. Connect a grounding lead between the Attenuator/RPP housing and the
Output Module. Program the UUT to +10 dBm and check continuity with an
ohmmeter from J1 through to C7. Be sure that the RPP is not tripped. Tracing through
the Attenuator/RPP may find a defective relay contact.
RPP trip operation can be checked using the test points provided on the Relay Driver
PCA. Connect a power meter to the UUT RF OUT connector and program the UUT
to SPCL 01 and then set level to +10 dBm. A momentary short across the terminals of
TP1 should trip the RPP causing the observed output power to drop by more than 30
dB. Failure indicates a problem with U1-A, U1-D, Q8, Q9, K8, or associated circuitry.
The RPP can be reset by pressing the RF ON button. The RPP itself can be reset by a
momentary short across TP2 but this will not reset the rest of the UUT to RF ON.
Failure indicates a problem with U1-B, U1-A, or associated circuitry. Program the
UUT to amplitude fixed range (SPCL 51) and edit the level to -10 dBm using the knob.
Place a clip lead short across TP3. This will allow the RPP to trip at low RF levels.
Now edit, with the knob, the level upwards in 1 -dB steps. The RPP should trip prior to
reaching +13 dBm. Failure indicates a problem with CR1 (on the Attenuator/RPP
PCA) or with U1-A, U1-D, Q8, Q9, K8, or associated circuitry (on the Relay Driver
PCA).
ATTENUATOR
6 dB
12dB
24 dB #1
24 dB #2
24 dB #3
24 dB #4
24 dB #5
Table 6D-5. Attenuator Levels
PROG LEVEL SPECIAL FUNCTION
+6 dBm
0 dBm
-12 dBm
-12 dBm
-12 dBm
-12 dBm
-12 dBm
TROUBLESHOOTING AND REPAIR
OBSERVED LEVEL
(NOMINAL)
+6 dBm
0 dBm
-12 dBm
923 -12 dBm
924 -12 dBm
925 -12 dBm
926 -12 dBm
RF LEVEL/AM
6D-28.
6D-21