Fluke 6080A Service Manual page 221

8. Using an oscilloscope, check for the presence of a 2V p-p sine wave at TP4 and
measure its amplitude with an AC voltmeter to verify it is 0.7071V rms within
±0.1% (±0.7 mV). If the sine wave is not present or is distorted, check S1, S2
(U10), and U9B and associated components. If amplitude is slightly off, recalibrate
(R9) using normal calibration procedures.
9. Using an oscilloscope, verify the presence of a 4.66V p-p (±5%) sine wave signal at
TP9 and check for visible distortions. If the sine wave is not present, is distorted, or
is of the wrong amplitude, check level DAC U8, and U11A. If U8 and U11A are
OK, it could be a write data error that could result from a faulty U1 or an interface
bus fault.
10. Using an oscilloscope, verify the presence of a zero centered 8V p-p sine wave at
TP5. If the signal is distorted, check U11B and associated resistors (R11, R12,
R13) and switches (S3, S4). With an AC voltmeter, check for 2.8284 V rms ±0.1 %
(±2.8mV). If the signal not within specified accuracy, recalibrate (R13) using
normal calibration procedures.
S1-S6 refer to analog switches on the Modulation Oscillator.
Pulse Generator Troubleshooting
To troubleshoot the pulse generator, proceed as follows:
SETTING UP:
1. Put instrument into preset default state by selecting entering SPCL 758.
2. Set up the instrument for internal pulse operation (SPCL 741).
3. Enable INT AM modulation.
4. Enter MOD FREQ of 10 kHz (100 us period).
5. Set the pulse width to 25 us (SPCL 759).
TEST PROCEDURE:
Modulation level control has no effect in pulse mode.
1. Verify the presence of a 10.0-MHz logic signal at TP10. If no signal is present at this
point or the signal is the wrong frequency, either U1 is faulty, a data write error has
occurred, or the 20-MHz signal is inadequate.
2. Using an oscilloscope connected to TP11, verify that the TTL level PULSE signal
from U1, is at 10 kHz and that it has a positive pulse width of 25 us. If not, it is
probable that U1 is faulty.
3. Using an oscilloscope, verify that the TTL level PULSE described in step 2 above is
present at TP5.
4. Using an oscilloscope to observe TP4, verify that the same pulse shape described in
step 2 is zero centered, with an amplitude of 2V ±10% p-p. If either the amplitude
or wave shape is incorrect, check U5 and the associated resistors (R22, R23, R24,
R25).
NOTE
TROUBLESHOOTING AND REPAIR
INTERNAL MODULATION OSCILLATOR
6F-8.
6F-5/6F-6