Fluke 6080A - Modulation Check 6 E-14.; Input Signals and Control Input Signals Checks 6 E-15.

TROUBLESHOOTING AND REPAIR
FREQUENCY AND PHASE MODULATION
Modulation Check 6E-14.
For errors and faults in modulation, use Table 6E-4.
Table 6E-4. FM Oscillator Modulation Control (Normal Operation)
NOTE: Set SPCL 909, RF Freq 800 MHz, INTFM DEV 250 kHz @ 1 kHz (Alternate: Use EXTFM
with low frequency signal generator, JF 6011 set to 1 kHz and 383 mV RMS into EXT FM input.)
MOD FREQ
100 Hz
1 kHz
5 kHz
VOLTAGE AT
TP4
500 mV-peak
500 mV-peak
500 mV-peak
SIGNAL AT JUNCTION
U38-1/C70
250 mV-peak
25 mV-peak
< 5 mV-peak
SIGNAL
TP1
4 p-peak
4 p-peak
4 p-peak
To check modulation, proceed as follows:
1. First check FM input to FM PCA at J6 for 4V-peak. If this is not present, check
Modulation Control PCA FM circuitry and inputs.
2. For error at TP4 and TP1, check the high modulation frequency path, U40, etc.
3. For error at the U38-1/C70 junction, check the low frequency modulation path
U38, etc
4. Check all ranges for modulation correctness at output. Use the Modulation
Control Table (Table 6E-1) for the logic and the ranges for all FM DEV ranges.
Check CMOS analog switches and drivers for proper operation.
5. Check Phase Modulation for correctness at output. If the output is not correct,
check the øM circuits associated with U40 for problems at high modulation
frequencies; for errors at low modulation frequencies check the øM circuits
associated with U38.
6. For errors in Special Functions LORATE FM and HIRATE, øM check the
circuits associated with U40 and U38.
7. For errors in DCFM, check circuits associated with FM Steer and U5 and circuits
with the loop amp U25 and relay K4, and the LODCFM detector U27. Also check
the FM Steer circuits on Modulation Control PCA. The process is implemented by
the controller.
Input Signals and Control Input Signals Checks 6E-15.
Check the input signals and control input signals as follows:
1. If the modulation signal is not present at J6 FM, check the Modulation Control
PCA (A11) for the FM DAC and amplifiers and switch inverter.
2. If the 20 MHz is not present from the Output PCA (A8), check the switched +5Vsw
on J4, and the +5V DC on J7 to the Output PCA.
3. If the control signals are not correct on J1 according to the Modulation Control
Table (Table 6E-1), check the latches on the Modulation Control PCA (A11).
6E-12