Thanks for valuable comments John ?
I will try to verify the Power Supply levels as well as inspect the caps on it first to make sure the caps in the PSU are not bad/getting bad.
The power meter is on the RF I/O? input only.? ? You can get an input level on the ANTENNA but that's usually with the SA .....at least that's how I normally do it.
Thast is how I also do it when using ANT IN port.
However, when I read page 65 in the "Assembly Level Repair" document at
it suggests a TX power reading available when using the ANT IN port when diagnosing faults in the RF Analyzer section:
To isolate the RF Analyzer:
? On the Test Set:
? Press PRESET.
? Press TX.
? Set Tune Mode to Manual. .
? Set Tune Freq to 100 MHz.
? Set Input Port to Ant.
? On the external RF signal generator:
? Set the frequency to 100 MHz CW.
? Set the amplitude to 0 dBm.
? Connect the output to the Test Set¡¯s ANT IN connector.
? Set the RF signal generator frequency to 100, 500, and 900 MHz. For each frequency,
the TX TEST display on the Test Set should read as follows:
? TX POWER should read approximately 0.001 ? for each frequency.
? TX FREQUENCY should read 100, 500, and 900 MHz respectively.
? If the Test Set has a Spectrum Analyzer, temporarily select SPEC ANL and note the
level and frequency of the signal¡¯s fundamental component. (Press TX to return to
the TX TEST screen.)
However, as the last paragraph says, TX level has to be chosen to see TX power if the unit has the SA module installed?
I usually? run the MISC DIAGS? as well to verify all three RF ports and often pull the RF I/O module and open to inspect for any over power if I have the unit open.
Ok will test that as well tonight. Will inspect the RF I/O module during the weekend.
The diagnostic mostly uses the calibration signal internal to the card to test.? May have a bad LO output MMIC on the card.? Sometimes the RF chokes open up as well.
Ok, do you mean a bad LO outut MMIC on the SA module itself?
Ah! Reading page 643 in the Assembly Level document indicates that this calibration signal is on the SA card.
I am looking in the schematic for the SA module from the CLIP-files for the 8920A and I see the section of the schematic for the calibration signal but not sure which of the IC:s there would be LO output MMIC?
Would it be U3A, U3B and/or the U10A?
