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Maintainance of 2753p and peak drift

Torquil Macdonald Sørensen
 

Hi!

Three questions about a 2753p spectrum analyzer:

1) The unit can store graphs and configuration settings, so it has a
battery. Is there a danger of losing calibration data if the battery fails,
or is it only used for what I mentioned above? I would hate to be forced to
attempt to calibrate of this thing.

2) Does the unit contain SMD capacitors that should be changed as soon as
possible to avoid collateral damage od the pcb or other components?

3) I'm experiencing that spectrum peaks are drifting somewhat between each
sweep when the digital view is activate. For each frequency sweep, a given
peak will have drifted somewhat in one direction, until after a few sweeps
it again appears at around the original position, so it is kind of cyclic.
I think it only happens when the digital view is active. It is more
pronounced for low frequency peaks, maybe because the amount of drift is
absolute in hz/s, not relative to the frequency value. Anyone seen this
before?

Best regards,
Torquil Sørensen, Norway

John Miles
 

1) The unit can store graphs and configuration settings, so it has a
battery. Is there a danger of losing calibration data if the battery fails,
or is it only used for what I mentioned above? I would hate to be forced to
attempt to calibrate of this thing.
No calibration info is stored, only graphs, settings, and macros (for those units that support them).

2) Does the unit contain SMD capacitors that should be changed as soon as
possible to avoid collateral damage od the pcb or other components?
This depends more on the production date than on the model number. See http://www.ke5fx.com/49x_notes.pdf for some suggestions on what to look for.

3) I'm experiencing that spectrum peaks are drifting somewhat between
each
sweep when the digital view is activate. For each frequency sweep, a given
peak will have drifted somewhat in one direction, until after a few sweeps
it again appears at around the original position, so it is kind of cyclic.
I think it only happens when the digital view is active. It is more
pronounced for low frequency peaks, maybe because the amount of drift is
absolute in hz/s, not relative to the frequency value. Anyone seen this
before?
Likely normal, depending on the span. Off the top of my head, I don't recall whether it's the first or the second LO that is allowed to drift slightly between sweeps before being relocked, but it's described in the manuals. If you're not getting error messages, you are probably OK.

It wouldn't be a bad idea to go through the LO subsystem calibration in service volume 1. This isn't too time-consuming, and can give you some confidence in the adjustment margins of the various trimpots. But there's also a case to be made for not 'fixing' it if it's not broken.

-- john, KE5FX

Torquil Macdonald Sørensen
 

On 09/03/2020 00:34, John Miles wrote:
3) I'm experiencing that spectrum peaks are drifting somewhat between
each
sweep when the digital view is activate. For each frequency sweep, a given
peak will have drifted somewhat in one direction, until after a few sweeps
it again appears at around the original position, so it is kind of cyclic.
I think it only happens when the digital view is active. It is more
pronounced for low frequency peaks, maybe because the amount of drift is
absolute in hz/s, not relative to the frequency value. Anyone seen this
before?
Likely normal, depending on the span. Off the top of my head, I don't recall whether it's the first or the second LO that is allowed to drift slightly between sweeps before being relocked, but it's described in the manuals. If you're not getting error messages, you are probably OK.

It wouldn't be a bad idea to go through the LO subsystem calibration in service volume 1. This isn't too time-consuming, and can give you some confidence in the adjustment margins of the various trimpots. But there's also a case to be made for not 'fixing' it if it's not broken.

-- john, KE5FX

Thanks, that is very helpful to know! I guess I will have to have a look
at the other service manuals that I have managed to download
(492/494/496/2754/...) I was not able to find a downloadable service
manual for the 2753, or the 495 with the same frequency range. Would you
happen to know the frequency ranges for the 1st and 2nd LO in this unit?
Surely it is different from the higher frequency units?

I would also like to do some audio work with this unit since it goes
down to 100 Hz, but the peak drift problem is a bit too much at those
low frequencies. I think the peak drift is actually dependent on if I
use the peak locate feature button or not during the sweeping.

But I think the first items that need to be addressed are: noisy fan,
check electrolytics/SMD electrolytics/RIFA capacitors and look at the
state of the battery. The serial number is B030249 and it was apparently
owned by Boeing before, according to the stickers. The latest
calibration was done in 2002.

Torquil