Fluke 6060B Instruction Manual page 169

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40-47. ALC Loop Control Voltage
PROCEDURE
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l . Connect a l V peak (2V p-p), 1-kHz signal source to the external MOD IN PUT.
Program the UUT for 350 M Hz, 7 dBm, 7 1 % AM depth, and EXT AM ON.
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3 . M easure the ac and the d e voltage at TP7. The rms voltage should be nominally
50% of the de voltage.
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4. Program the UUT for 35% AM depth. The rms voltage should be nominally
25% of the de voltage.
If the UUT fails this test, the problem lies somewhere between the EXT MOD input and
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TP7 (ALC loop-control voltage), To further localize the problem, the same test can be
done by measuring the ac voltage at U302 pin 8 (input to level DAC). If the measured ac
voltage does not change as programmed AM depth is changed, eitherthe A M DAC or its
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control is at fault. The AM OAC (A2A4U30 1 ) is an 8-bit DAC and is set to twice the
programmed A M depth, e.g., 1 80 for 90% A M .
I f the U UT passes this test, then the A L C loop control voltage i s correct, and the problem
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is in the ALC loop. A likely cause of excessive AM depth error and harmonic distortion is
detector non-linearity_ The following test checks detector linearity.
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40-48. Detector Linearity
PROCEDURE
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Install the plate covers and let the UUT warm u p at room temperature for one
hour.
2. Program the UUT for 350 M Hz, 12 dBm, modulation OFF.
3. Program [SPCL] [8)[ I ] and [SPCL) [9][ 1 ] to disable level correction and enable
amplitude fixed range.
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4. Measure power with a power meter at the UUT RF OUTPUT. Note the reading.
5. Program the UUT for 2 dBm using the EDIT keys. The measured power should
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be 1 0 dB ± 0.2 dB below the reading noted in step 4.
6. Program the UUT for -8 dBm using the EDIT keys. The measured power
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should be 20 dB ± 0.4 dB below the noted reading.
7. Program the UUT for [SPCL] [0][0).
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If the UUT fails this test, the problem is likely to be in the detector or detector-linearizer
circuit. If the UUT passes the test, the problem is constrained to the other ALC loop
elements, and is likely to be a bandwidth problem associated with the loop amplifier or
I the modulator or modulator-lineari�er circuit.
40-49. RPP
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When servicing the A2A5A2 Attenuator j RPP Control PCB, use the three d
points to aid in the troubleshooting of the assembly. The RPP can be t
protect position) by momentarily shorting the two points of TP
Control
MAINTENANCE
TROUBLESHOOTING ANO REPAIR
u
pin test
al -
r e
d (to the
I . ipp
It can be reset by
40-21