Tektronics DSA71254C Oscilloscope issue - Page 1
Forum section: electronics / testgear

author: jongs
author_rank: Newbie
timestamp: April 01, 2025, 08:44:25 am
content: Hi.I am using a Tektronics DSA71254C. However, it suddenly started showing the following symptoms and is not measuring correctly. This waveform is from measuring a 140MHz pulse. The diagnostics show no issues, but there's an error during calibration. The repair company says they can't find the cause.Have you ever seen these kinds of symptoms before?

author: coromonadalix
author_rank: Super Contributor
timestamp: April 01, 2025, 10:25:57 am
content: can you post the diagnostic screen ?

author: stj
author_rank: Super Contributor
timestamp: April 02, 2025, 09:17:30 am
content: interesting that it's worse on the transition than the peaks.could it be capacitance on the input?

author: KrudyZ
author_rank: Frequent Contributor
timestamp: April 03, 2025, 03:46:19 am
content: Do all channels show the same problem?

author: jongs
author_rank: Newbie
timestamp: April 03, 2025, 04:45:57 am
content: The equipment came back from the repair shop today, and I will check it and post about it.

author: jongs
author_rank: Newbie
timestamp: April 03, 2025, 04:51:41 am
content: And the output signal on the front of the scope is the same even when measured. The results are the same for all channels as well.

author: jongs
author_rank: Newbie
timestamp: April 03, 2025, 06:11:15 am
content: The Diagnostics result and Calibration result are as follows.When measuring by connecting a fast edge signal to the front of the scope, the edge is greatly affected by the BW.

author: jongs
author_rank: Newbie
timestamp: April 03, 2025, 06:12:41 am
content: test result.

author: jongs
author_rank: Newbie
timestamp: April 03, 2025, 11:30:13 pm
content: Please give me any opinion or suggestion.

author: KrudyZ
author_rank: Frequent Contributor
timestamp: April 04, 2025, 03:36:36 am
content: Try turning on all four channels at the same time, no need to hook up anything to the other channels.This will reduce the sample rate from 100 to 50 Gs/s.If this changes the trace then it is likely caused by a defect in the interleaving to the ADCs.I don't know how this specific instrument is built, but many of the high end units use several ADCs in parallel to get to the high sample rates and then interleave them.The bandwidth setting is very likely a digital filter rather than a switchable analog front end low pass, so it could filter out the interleaving errors, creating much cleaner signals for the lower bw settings.This is all just a somewhat educated guess, though.EDIT: I see that you are already at 50 Gs/s. In that case see if you can increase the sample rate to 100Gs/s which would use a second channel ADC and might make things even worse (or not)

author: jongs
author_rank: Newbie
timestamp: April 04, 2025, 04:49:44 am
content: 50Gs/S result and 100Gs/s result.

author: 44kgk1lkf6u
author_rank: Regular Contributor
timestamp: April 04, 2025, 02:11:05 pm
content: The marker on the screen does not line up with the transition in the waveform. Is it normal or did it show up along with the problem?Can you save the data in CSV in addition to a screenshot? Then people can try to see if there is some pattern in the glitches.What happens if you trigger on something else? You can set the oscilloscope to trigger on mains, and then capture single shots until an edge shows up on the screen. If that gets rid of the glitches, then we know the problem is likely related to the trigger stuff.

author: dxl
author_rank: Regular Contributor
timestamp: April 04, 2025, 07:46:33 pm
content: Looks to me like broken calibration data (ADC interleave calibration). I don't know how many ADCs this scope has, but usually they are using 4 or more ADCs with higher sample rate. Can you test whether this problem also happens with low sample rates? Like a few MS/s?EDIT: Ah, KrudyZ mentioned that already. Nevermind then.

author: dxl
author_rank: Regular Contributor
timestamp: April 04, 2025, 08:05:17 pm
content: I found some records from modifying my tekscope software (I have a MSO70404 where one ADC is broken, so i had to modify the firmware to ignore that).From my records there's a telnet port 1072 where the tekscope software listens for commands. This can be used to move the phase of each ADC with the 'a2dPhase' command. My records say:Code:A2DPhase <X> <Y>Y=0 - 3X0,1 = Ch12,3 = Ch24,5 = Ch36,7 = Ch4# 12.5GS/s no fastacqA2DPhase 0 0 -10A2DPhase 0 1 -15A2DPhase 0 2 -0A2DPhase 0 3 0So X is the channel, while Y is the ADC. My scope has 25GS/s iirc, and each channel has 4 ADCs, so 16 ADCs in total. I would assume that if your scope has 100GS/s it has even more ADCs. Guess it would be pretty hard to align the phases of all ADCs manually.

author: dxl
author_rank: Regular Contributor
timestamp: April 04, 2025, 08:10:57 pm
content: My scope logs all kinds of debug to c:\TekScope\calibration, console.log and calidiag.log might be of interest. Although you should get SPC fails if there's a problem in there. But it doesn't hurt to take a look...

author: nctnico
author_rank: Super Contributor
timestamp: April 04, 2025, 08:13:44 pm
content: To the OP: can you switch the scope to dot mode? If yes, post an image of that. This will probably reveal a repetetive pattern where some samples are OK and some are completely off.

author: jongs
author_rank: Newbie
timestamp: April 07, 2025, 01:14:58 am
content: Thanks, everyone.I checked the logs and found a failure record on March 21. There are no other failure records before that date. Coincidentally, another engineer connected a laptop to the GPIB on that day. It seems like there might be a connection, but I'm not sure if it's a software or hardware issue.The fail log starts from line 369.**********************************************************acquireData2 failedPhase cal pass 2acquireData2 failedPhase cal pass 3acquireData2 failedPhase cal pass 4acquireData2 failedERROR (0xffffffff): digPhaseCal failedCh1: 06:54:25 Attached 1X SN:N/A v0.0 Delay: 0.000e+000sCh2: 06:54:25 Attached 1X SN:N/A v0.0 Delay: 0.000e+000sCh3: 06:54:26 Attached 1X SN:N/A v0.0 Delay: 0.000e+000sCh4: 06:54:26 Attached 1X SN:N/A v0.0 Delay: 0.000e+000s

author: jongs
author_rank: Newbie
timestamp: April 07, 2025, 05:36:28 am
content: I updated the firmware to the latest version, from 7.6.1 Build 5 to 10.8.7 Build 29. I was able to see the SPC failure message in the console.log.**********************CAL: SPC failed, checksum mismatch, expected 13500 found 4069713:50:15:790 tmgrclass.cpp:TmgrStartup(2237) tmgrTaskInitFailure to open Multiscope Registry.Multiscope Mode: StandAloneCalling rtlStartup.....