Have had this 2755AP for 10+ years; for the first time in recollection I've needed to use very narrow span width (to inspect output of a HP synthesizer). Frequency being inspected is 1000 MHz. When span is set to 500 Hz/div, I get occasional "Tuning failure 2nd LO". When span is set to 200 Hz or 100 Hz/div, the error messages are more frequent but not continuous. The error message does not appear at power-up self-test.
I used Shift 0 3 to access "2ND LO DIAGNOSTIC AID".
Doesn't appear I can post the photo here, but this is the displayed info:
TUNE VOLTS NOMINAL=0.01V DAC SET = 0.19V
2ND LO FREQ DESIRED = 2.182.000GHZ COUNTED = 2.182.099GHZ
OFFSET FREQ DESIRED = 18.000 000MHZ COUNTED = 17.900MHZ
OFFSET SETTING ACCURACY 294.912KHZ
The verbiage in the service manual (volume 1, page 6-12, section titled "TUNING FAILURE - 2ND LO" includes the text
"The offset setting accuracy is the maximum permitted difference between the actual and desired offset frequencies. The setting process ends when the difference becomes less than or equal to this value. The tolerance depends on frequency span and band."
I'm puzzling over what this is trying to tell me.
Also I believe the analyzer has a built-in back-up battery which has not been touched in at least the 10 years I've had the unit here. Does the back-up battery store some calibration coefficients that could have been lost? There has been no error message related to back-up battery specifically.
Thanks!
Dave
