Products > Test Equipment

DSA875, damaged?

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RFDx:

--- Quote from: grg183 on June 20, 2023, 03:26:53 pm ---At the time of the damage I had it set on 2.508GHz with 10MHz span, 30dB internal attenuator, 20dBm reference level and the signal was displayed top flattened on the 20dBm mark, later I found the connected device was outputting around 26dBm.
--- End quote ---

The damage level with 30dB attenuation is above 30dBm. I don't think the frontend is damaged. Does the attenuator still work? Does the preamp increase the level by ~17dB? Your 26dBm input signal and the additional attenuation of exactly 26dB doesn't seem to be a coincidence. Did you somehow change the "reference level offset" by 26dB? A level setting somewhere in the menu could be off.

tautech:

--- Quote from: RFDx on June 21, 2023, 03:03:23 pm ---
--- Quote from: grg183 on June 20, 2023, 03:26:53 pm ---At the time of the damage I had it set on 2.508GHz with 10MHz span, 30dB internal attenuator, 20dBm reference level and the signal was displayed top flattened on the 20dBm mark, later I found the connected device was outputting around 26dBm.
--- End quote ---

The damage level with 30dB attenuation is above 30dBm. I don't think the frontend is damaged. Does the attenuator still work? Does the preamp increase the level by ~17dB? Your 26dBm input signal and the additional attenuation of exactly 26dB doesn't seem to be a coincidence. Did you somehow change the "reference level offset" by 26dB? A level setting somewhere in the menu could be off.

--- End quote ---
Running Preset will fix that.
It's damaged for sure.

grg183:

--- Quote from: RFDx on June 21, 2023, 03:03:23 pm ---The damage level with 30dB attenuation is above 30dBm. I don't think the frontend is damaged. Does the attenuator still work? Does the preamp increase the level by ~17dB? Your 26dBm input signal and the additional attenuation of exactly 26dB doesn't seem to be a coincidence. Did you somehow change the "reference level offset" by 26dB? A level setting somewhere in the menu could be off.

--- End quote ---

That's an interesting observation, it does seem weird for it to be a coincidence! However as tautech says the Preset should fix that. Its still really weird that it's still measuring but just attenuated.
I confirm that the pre-amp and internal attenuator are still working correctly and they are applying the expected amount of gain and attenuation also in the < 3.2Ghz range.

I will try to double check that it is not the TG but that was not in use at the time and I was seeing the same attenuation on my signal as well, so that is unlikely.

 Contacted Rigol service center and they say it is a damaged receiver, their only option is a ~€4k full motherboard swap :(
I will probably just get a SSA3075X-R to replace it and keep the DSA875 as a spare knowing that the reading is off, or even just as a generator. I don't see it making sense spending that much money to repair it.

RFDx:

--- Quote from: grg183 on June 22, 2023, 09:28:21 am ---I confirm that the pre-amp and internal attenuator are still working correctly and they are applying the expected amount of gain and attenuation also in the < 3.2Ghz range.
--- End quote ---

This means the damage must be somewhere in the 1. IF section. A fault in the fixed frequency IF would manifest as a flat but attenuated amplitude plot. The upper 3.2...7.5GHz range probably downconverts directly to the 2nd IF and still works as expected.

grg183:

--- Quote from: RFDx on June 23, 2023, 01:33:40 am ---
--- Quote from: grg183 on June 22, 2023, 09:28:21 am ---I confirm that the pre-amp and internal attenuator are still working correctly and they are applying the expected amount of gain and attenuation also in the < 3.2Ghz range.
--- End quote ---

This means the damage must be somewhere in the 1. IF section. A fault in the fixed frequency IF would manifest as a flat but attenuated amplitude plot. The upper 3.2...7.5GHz range probably downconverts directly to the 2nd IF and still works as expected.

--- End quote ---

I think that is an excellent observation! It's probably 'just' the IF amplifier damaged. I will definitely have a look inside and see if I can identify the IF section and troubleshoot it somehow.
I'm definitely not spending 4k+ to repair this.

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