Perpelxing issue with a DPO3054

I have a DPO3054 which required calibration. But it was working fine and passing SPC all the time
I sent it in to Keysight Cal Lab and they performed full performance tests before and after factory adjustments were done
and scope was passing SPC and all tests were excellent and in spec
so I receive the scope and right out of the box it fails SPC (after warm up) and also has about 1mV DC balance (offset) at 1mV/div
on ch 3 and 4 and a less on channel 1 and 2 but still out of spec even though the "after" test show it was about 0.03mV

so I sent it back to Keysight lab and right away the scope passes SPC 4 times and another full performance test shows it is in spec
and the technician ran SPC for me several more times and it passed

I receive the scope and exactly the same issue as before :-( :-(

I moved it to other rooms in the house and also into the basement but it never passes SPC

any idea!!??
 

Hello,

I apologize, but this is a strange issue.

I've discussed this request with our development and service teams and we have a few ideas:

Have you tested this on different line power? i.e. at your office or another building?

This could be a power supply issue.

If you continue to experience this issue, I would recommend returning the scope to Tektronix for evaluation.

This way, we can verify the product directly: https://www.tek.com/en/service-quote

Unfortunately, we can't verify what was performed by the other calibration lab and can't comment on their findings.

However, are there other members of the user community who have experienced a similar issue?

Hopefully, other forum members can also weigh in here.

I hope this has been helpful.

Tektronix Applications Engineer

yes I also used it with an isolation transformer and chagned the voltage to other than 120V (tried down to 100V) but didnt help<br> I dont think my house is particularly humid or hot either...but the scope passed SPC whenever it was with Keysight lab<br> the date of the last passed SPC in the scope also verifies that it did pass when it was there.<br> <br> <br> &nbsp;

Hello,<br> <br> Does the MDO's Self Test utility report any failures? <ol> <li>Push Utility</li> <li>Push Utility Page and then select Self Test</li> <li>Push OK Run Self Test</li> </ol> <br> I agree with Jacob my first thought was, "what is different between your house and the cal lab?" and that made me think about Line Power. Power Supply problems can manifest with strange symptoms. Another possibility is that the channel shows some offset drift only when the channel is open. Put a short or 50Ohm term on the channel and run AutoZero. AutoZero may remove that DC drift. It wouldn't, however, explain why SPC was failing. SPC is designed to run with the channels disconnected and open.<br> <br> I'm also curious what the cal lab adjusted. Our <a href="https://www.tek.com/en/manual/oscilloscope/mdo3000-service-manual-mdo3000">service manual</a> does not publish any adjustments that can be made by 3rd party cal labs. A Tek Service center would have much better diagnostic and repair capability.<br> <br> Sorry I don't have a guaranteed solution at this point.<br> <br> &nbsp;

no, self test always passes.<br> there is no autozero function<br> &nbsp;

My mistake I misread your title and was referencing MDO3000 support docs. The DPO3000 is a different instrument and has its own firmware and documentation. The service manual shows several adjustments available on the DPO3k including DC Voltage that the cal lab probably performed.

The most recent firmware is v2.40 released 6/20/2012. Could you try updating that? This instrument ended long term support in 2018 so it may be difficult to find parts if we discover its a hardware issue.

unit has always had latest firmware
I also tried 2.31 with no change

my best guess is that it is some kind of EMI issue...it may be generated by the scope itself but it is somehow enhanced when it is in my house.<br> I moved it to a very quiet room with absolutely no electrical equipment running (not even light bulbs) and it still failed<br> although strangely the amount of DC offset on ch3 and 4 was a little less.<br> I also made a haphazard shield (faraday cage but not quite) around the scope and then ran SPC and still failed<br> then when I sent it back to Keysight, it passed. I asked the technician to run it several times over a period of 5 days<br> and also to move it to another office and he did and it always passed so he sent it back to me ...<br> other than this the scope works and measurements are very accurate, BW is about 600MHz and pretty flat...DC ffset accuracy is good&nbsp;<br> and performance test data (done twice) also shows that everything is in spec...<br> <br> &nbsp;

Faraday cage is a good experiment to check for external EMI issues. If you short the CH3 and CH4 center pin to the shell of the BNC connectors, that would also show if any EMI is coupling in through the front end. I'm afraid if its an internal EMI source it may be harder to pinpoint and resolve. I haven't seen EMI issues display as a DC offset but it's not impossible.