Issue with my Siglent SDS1202X oscilloscope - Page 1
Forum section: electronics / repair

author: jfcen29
author_rank: Contributor
timestamp: March 22, 2025, 12:13:22 pm
content: Hello eveyone,I am facing to an issue with my Siglent oscilloscope SDS1202X.On both inputs the voltage measures are wrong.The issue appears from one day to the other but at the beginning I could observe the signal with a poor quality like the ground of the probe was disconnected.But now there is no trace.Here below what I observe on my scope.For example, in auto mode trigger, no signal on the inputs, I cannot see the trace on the scope on both inputs. Look at the two pictures default_setting_ch1.png and defaut_setting_ch2.png.If I want to set the ground on both channels, there is an offset. This offset depends on the vertical calibration.( Loot at the picturech1_and_ch2_set_gnd.png).If I try to mesure a simple DC signal of 5V, there is no trace on the display. Loot at the picture dc_signal_input.png.If I try an "auto setup" by clicking the dedicated button, the setup seems to be completely crasy. Look at the picture autosetup.png.I tried to do a self calibration but it didn't fix the issue.I also reflashed the firmware with the latest version and also with the older version but it doesn't fix my issue.All other functionnalities of the oscilloscope seem to be OK (display, keyboard, network for catching the sceenshots, etc...)By reading the service manual, I checked the different tension of the power supply and also of the mainboard.I noted this different values of tension (I have not the schematic of the board):from the connector of the power supply:=======================================pin1,2: 6.532V (normal range 6.3- 6.6V) => OKpin3: -9.510V (normal range -9.1- -9.5V) => just out of the range. Don't think it could be the issuepin8: 15.296 (normal range 14.8- 15.2V) => just out of the range. Don't think it could be the issueOn the mainboard, no signal on the inputs, fan unplugged============================================================theorical tension measured tension test point number status6.5V 6.484V borne L48 OK1.5V 1.5132V TP69 OK1.2V 1.2294V TP64 OK1.8V 1.9196V TP16 OK5.0V 5.017V TP61 OK5.0V 5.032V TP103 OK3.3V 3.305V TP20 OK-5.0V -4.917V pin of C1014 OK-5.0V -4.958V pin of C1009 OK-9.3V -9.526V TP100 just above the range (normal range -9.1- -9.5V)10.4V 10.348V TP (no number) OK1.35V 1.3227V TP66 OK15.0V 15.258V TP59 just above the range (normal range 14.8- 15.2V)3.3V 3.351V TP62 OK2.5V 2.518V TP50 OK5.0V 5.107V TP96 just above the range (normal range 4.9 - 5.1)From my point of vue, the different tensions seem to be good.I look at the mainboard. It is very clean, no burned point, no blowed component.I always work with very low voltages on the inputs (<20V).Here is the system info:software version: 1.12.15R10FPGA version: 17.3.10hardware version: 3-3product type: SDS1202Xserial No:SDS1XDC4162941Is there someone that observes the same troubles?Do you think that is a software or hardware issue?Any help would be very appreciated.Feel free to ask me any other information if needed.Thanks in advanced.Best regards

author: Swake
author_rank: Frequent Contributor
timestamp: March 22, 2025, 05:13:21 pm
content: Pics were not attached or linked.I guess most people understood what is meant here, just to avoid any confusion: 'tension' is French for 'Voltage'.It sounds more like an hardware issue than a software issue.This scope has 2 separate and identical front ends. As the issue seems to be on both channels it likely concerns a common component. Might be related to AD conversion (a HMCAD1511 ?) or some part in the trigger circuit is dead.You might want to try connecting a known input signal and trace it on the PCB with another scope to see till were it gets.Could you share the service manual? I guess there is some block-diagram or similar.

author: 2N3055
author_rank: Super Contributor
timestamp: March 22, 2025, 07:16:56 pm
content: ADC are also separate.I would check more the analog supplies for front end, negative and positive ones.there are 32 voltages to check.EDIT :Sorry for confusion.

author: Swake
author_rank: Frequent Contributor
timestamp: March 22, 2025, 08:03:08 pm
content: The SDS1202X is not part of the SDS2000 series. That service manual does not apply.

author: jfcen29
author_rank: Contributor
timestamp: March 23, 2025, 05:40:48 am
content: Hello everyone,Thanks a lot for your answers.I don't understand why the pictures are not linked to my first message.I am going to try again.Here is the service manual for the SDS1000 serie. Unfortunately I didn't see any block diagram in this document.As you said Swake, I think that the issue is due to a common component of the two channels. First, I though that the power supply would be the same one for the two channels but it seems there is one power supply by channel.I will try to investigate deeply by injecting a known signal...

author: jfcen29
author_rank: Contributor
timestamp: March 23, 2025, 05:45:40 am
content: Here is the service Manual.It was not linked in my previous message

author: tautech
author_rank: Super Contributor
timestamp: March 23, 2025, 08:19:24 am
content: Run Self Cal.Then show us probe compensation output screenshot with input attenuation and probes set to 10x.Result should be ~3V p-p @1kHz

author: Swake
author_rank: Frequent Contributor
timestamp: March 23, 2025, 08:32:27 am
content: Dave did a teardownTrigger circuit:https://youtu.be/slBXLf4YKtA?t=954ADC:https://youtu.be/slBXLf4YKtA?t=994

author: jfcen29
author_rank: Contributor
timestamp: March 23, 2025, 11:15:55 am
content: Here are the results for each channel

author: jfcen29
author_rank: Contributor
timestamp: March 23, 2025, 12:09:40 pm
content: definitely, uploading pictures is hard for meSame signal on channel 1

author: jfcen29
author_rank: Contributor
timestamp: March 23, 2025, 12:32:25 pm
content: @swakeThanks for the link.This teardown is more about the SDS1202x-E oscilloscope.The reference of mine is SDS1202X (without the E). The hardware is different even if there are some parts which seem very similar( second part of the front ends as explained in the video, same AD converter AD1511)

author: tautech
author_rank: Super Contributor
timestamp: March 23, 2025, 07:08:43 pm
content: Quote from: jfcen29 on March 23, 2025, 11:15:55 amCan you confirm the probes have been compensated in 10x mode ?However something doesn't look right as the probe compensation output should be 0-3V, not in the negative region.Tell us some history of this scope, have you had it from new ?

author: jfcen29
author_rank: Contributor
timestamp: March 23, 2025, 09:33:39 pm
content: yes I confirm that the two probes have been compensated.All voltage measures are wrong now.I bought this scope in april 2017 on the website of Siglent Europe .I used it for a few years as a hobbyist without any problem.One day I noted that my measures seem to be degraded like the ground of the probe was disconnected.I always work with voltages under 20V.Now, the scope is unusable.

author: tom66
author_rank: Super Contributor
timestamp: March 23, 2025, 10:19:39 pm
content: Do you have access to another scope that you can compare waveforms with?The failure of both channels in a similar way makes me think something common like a Vref has gone bad.

author: tautech
author_rank: Super Contributor
timestamp: March 24, 2025, 12:09:47 am
content: Quote from: jfcen29 on March 23, 2025, 09:33:39 pmIs this a Plus version with inbuilt AWG ?That both channels are affected is worrying, like their internal references are lost or broken.Can you confirm BNC shells connection to mains PE is intact and still connected ?Difficult to find without another scope.

author: MathWizard
author_rank: Super Contributor
timestamp: March 24, 2025, 03:17:20 am
content: What does the measurement function/stats say ? I'd turn that on and choose some vertical measurements.I've heard people refer to voltage as a tension before, but I didn't know the French call it that. Ampere was French, but Volta was Italian iirc.

author: 2N3055
author_rank: Super Contributor
timestamp: March 24, 2025, 06:19:14 am
content: Quote from: MathWizard on March 24, 2025, 03:17:20 amIn my country it is called "napon" which is something akin to stress of tension or "električna napetost" which is electric tension. But people also call it "voltaža" colloquially, which is, well, voltage, but French like pronunciation...Many non English countries adopted word from French use directly.

author: Swake
author_rank: Frequent Contributor
timestamp: March 24, 2025, 06:33:35 am
content: You measured the voltages of the power supplies, please check if this is a 'clean' signal, as in not having ripple. You would need another scope for that unfortunatelyps: 'Electric tension' comes back in several languages (translated to 'spanning' in Dutch for example) and, as far as I know, dates back to a time that the 'Volt' was not yet named officially. It does not seem to be used in English very much. 'Electric potential' is more common and is also used in French and Dutch and probably many other languages. As to which is more accurate or less wrong I have no idea.

author: tautech
author_rank: Super Contributor
timestamp: March 24, 2025, 07:24:16 am
content: High Tension (HT) and Extra High Tension (EHT) are in common use in CRO service manuals.HT normally refers to CRT plate voltages, some 100-150V whereas EHT is the CRT Cathode voltage, negative 1-3kV, voltages depending on maker and model.Post Deflection Acceleration (PDA) voltages are next level again, normally 3 or 5x EHT which we don't ever go near !Early low BW CRO's didn't require PDA but as designs improved and BW increased it became a necessary evil.

author: jfcen29
author_rank: Contributor
timestamp: March 24, 2025, 07:54:55 pm
content: Quote from: tautech on March 24, 2025, 12:09:47 amNo, there is no inbuilt AWG.Yes I will check that BNC shell connection to mains PE is intact and still connected. I cannot to do that today.I have an other old analog scope. Do you think some stuffs that I can check ?I already inject a known signal on both channel and I can see the signal on both differential inputs of the AD converter.However I have to look it in detail to determine if it's ok or not...

author: jfcen29
author_rank: Contributor
timestamp: March 24, 2025, 07:59:45 pm
content: Quote from: Swake on March 24, 2025, 06:33:35 amYes sure I can do that too. I have an other old analogic scope. I cannot do that today but I will give you a feedback as soon as possible.

author: jfcen29
author_rank: Contributor
timestamp: March 24, 2025, 08:04:26 pm
content: Quote from: tom66 on March 23, 2025, 10:19:39 pmYes I already check the probe compensation output with an other scope. The signal is OK.

author: Grandchuck
author_rank: Super Contributor
timestamp: March 24, 2025, 08:07:43 pm
content: Quote from: tautech on March 24, 2025, 07:24:16 amHigh tension lines are those up on the huge metal towers running around country roads (here in the USA).

author: tautech
author_rank: Super Contributor
timestamp: March 25, 2025, 07:07:47 pm
content: Quote from: Grandchuck on March 24, 2025, 08:07:43 pmAs are the 11kV lines that supply our pole pig transformer and one could rightly claim also the 33kV HT lines that feed local substations or the 110kV or 220kV pylon feeds that supply regional substations ....but this is OT as it refers to powerco supply, not what is contained within an instrument.The modern instrument has gone the other way, apart from the mains supply all internal voltages are now low and considered no risk to the serviceman with ~15V now commonly max.Back to the OP......time for some datasheet study to discover what signal levels to expect WRT reference levels to find where the signal offset is going wrong.Hopefully it's just a dry joint affecting both channels or some part common to both of them.

author: tom66
author_rank: Super Contributor
timestamp: March 25, 2025, 10:55:12 pm
content: Quote from: jfcen29 on March 24, 2025, 08:04:26 pmSince you have another scope, I would input the same signal in, and check the signal at the ADC pins, highlighted in attached picture. It should be centered around 0.9V, half of the AVDD supply at 1.8V.HMCAD1511 has internal Vref generator (VCM output), but it can be defective potentially, or there could be too much load on it due to a fault elsewhere. It is good to eliminate bad ADC or bad signal processing in the attenuator stage.

author: jfcen29
author_rank: Contributor
timestamp: March 26, 2025, 10:29:00 pm
content: Quote from: tom66 on March 25, 2025, 10:55:12 pm

author: Swake
author_rank: Frequent Contributor
timestamp: March 27, 2025, 06:33:49 am
content: Quote from: jfcen29 on March 26, 2025, 10:29:00 pmDo I understand correctly this was for both channels? Because that is a very interesting finding. As you write, it seems related to the front-end. tautech's hope that it might be a dry solder joint gains momentum. A 'bad' contact can be in a wire, a connector, or eventually within a component.What else is common:- As mentioned before, there is the trigger circuit. But I would think the trigger circuit is not the one responsible to measure amplitude of the signal. And... it triggers...- A common power supply. You measured it already and found it stable, but was it ok when the signals disappeared entirely?- Some signal that controls something on the front-ends: such as the attenuators.Could you share a close-up picture from the front-end in your scope please (you already did, but it is not very readable) ? Similar to the one attached from Dave.

author: tautech
author_rank: Super Contributor
timestamp: March 27, 2025, 07:31:19 am
content: Actual SDS1102X front end image from a 2021 post:

author: tom66
author_rank: Super Contributor
timestamp: March 27, 2025, 02:41:19 pm
content: Please check the DC voltage of the ADC pins when no signal is injected (ideally, with a 50 ohm terminator BNC shorting the input, but if not, just clip the scope probe ground to the probe tip).

author: jfcen29
author_rank: Contributor
timestamp: March 28, 2025, 07:19:22 am
content: Quote from: Swake on March 27, 2025, 06:33:49 amYes you understand correctly. The signals are the same on both channels.I will check again the power supply when the signals disappear.In attachement you will find a close-up picture. Hope the quality will be suffisant. Tell me if it's not the case.At first glance, I didn't see any bad solder...Unfortunately, without schematic it's difficult to find what are the common parts for both channels

author: tautech
author_rank: Super Contributor
timestamp: March 28, 2025, 08:38:34 am
content: Don't overlook the mainboard is double sided so tracing signal paths is impossible when just one side is visible.We can't even get schematics.....

author: Swake
author_rank: Frequent Contributor
timestamp: March 28, 2025, 08:49:14 am
content: Indeed, at least 2, and I guess that board is going to be 4 or 6 layers at least.The picture is not very sharp indeed. Upload the max resolution you have please. Main goal is to identify the components and maybe distil something out of that.You made another interesting remark:QuoteWhile your measurement on the picture 'signal on BNC' shows 1Vpp. I would expect 3Vpp here too as the BNC is the place of injection. Difference might be related to input impedance somehow being very different between the 2 scopes. What is the source of the 1kHz signal? Is that from some known generator or the calibration signal of a scope?

author: tautech
author_rank: Super Contributor
timestamp: March 28, 2025, 09:03:35 am
content: Quote from: Swake on March 27, 2025, 06:33:49 amDon't overlook the VGA* that is controls some V/div and also BW as well as the 20 MHz BW limit.Dave explored these in a vid, I'll see if I can find it...it was a while back.*Variable Gain Amp

author: Swake
author_rank: Frequent Contributor
timestamp: March 28, 2025, 09:05:30 am
content: Would the small IC in the corner marked H1 (and marked H1K in other front-ends of Siglent scopes) be a ADA4932-1 ?

author: Swake
author_rank: Frequent Contributor
timestamp: March 28, 2025, 09:13:22 am
content: The chip just left from the relays in the last picture is likely a APO727 opamp in VSSOP package.

author: Swake
author_rank: Frequent Contributor
timestamp: March 28, 2025, 09:20:17 am
content: Is this the signal path?input on pin2 or pin3 of the OPA727 -> OPA727 Output pin6 -> input on pin2 ADA4932 -> ADA4932 differential out on pin10 & 11 -> input in the HMCAD1511 on channel 1 or 2pins for the channels:IN4 Negative differential input signal, channel 4 pin37IP4 Positive differential input signal, channel 4 pin38IN3 Negative differential input signal, channel 3 pin40IP3 Positive differential input signal, channel 3 pin41IN2 Negative differential input signal, channel 2 pin43IP2 Positive differential input signal, channel 2 pin44IN1 Negative differential input signal, channel 1 pin46IP1 Positive differential input signal, channel 1 pin47

author: tautech
author_rank: Super Contributor
timestamp: March 28, 2025, 09:30:26 am
content: Quote from: Swake on March 28, 2025, 09:05:30 amLikely so:https://www.analog.com/media/en/technical-documentation/data-sheets/ada4932-1_4932-2.pdfClues here:

author: tom66
author_rank: Super Contributor
timestamp: March 28, 2025, 09:38:42 am
content: Note that this scope has a digital trigger, so the trigger works by the FPGA capturing the ADC data continuously, modelling sinx/x response and calculating the actual trigger point that way. There may be a comparator for the 'EXT' trigger input, but that is not important for now.

author: jfcen29
author_rank: Contributor
timestamp: March 28, 2025, 08:50:59 pm
content: Quote from: Swake on March 28, 2025, 08:49:14 amAs you said I also expected to have a 3Vpp on the BNC connector.The source of the signal is the calibration signal of the siglent scope.(the scope which is out of service)

author: jfcen29
author_rank: Contributor
timestamp: March 28, 2025, 10:00:48 pm
content: Quote from: tom66 on March 27, 2025, 02:41:19 pmI did the measures that you asked by clipping the probe ground to the probe tip. (look at the attachement)The voltages are exactly the same on both differential inputs of the HAD1511. 1,55V on IP and 0,06V on IN.I also measured the supply voltage of the HAD1511 which is 1,91V. According the service manual, a normal range is between 1,7V and 2,0V .Do you expect such DC voltages? You talked in a previous post of voltages centered about half of the power supply...

author: tom66
author_rank: Super Contributor
timestamp: March 28, 2025, 10:05:43 pm
content: Yes, with no DC input I would expect both pins at 0.9V (strictly speaking, half the AVDD, 1.91V / 2 = 0.95V)I should clarify that offset should be set at ground level, please check the readings with vertical offset grounded.But it looks to me like the ADC is probably OK, the amplifiers before it are not working right. Since it is common to both channels, I would take a guess about a missing or faulty power rail.

author: jfcen29
author_rank: Contributor
timestamp: March 29, 2025, 10:04:21 am
content: Hello everyone,I have a good news.I managed to fix the issue.There was a drop of solder on one component just around the front ends. Look at the attachment.I removed this drop of solder very easily, and did a "Self Cal" again. Then the scope started again as before.I assume that this drop solder doesn't short the pins of the device for many years. I didn't do any solder on this siglent scopeThe component is marked "DEX" and seems to be an component from the "analog device" company. The package is a MSOP-8.A 74hc5410 (analog multiplexer/demultiplexer) is very close.I looked for its data sheet on the web, but I didn't find any releavant data sheet.Maybe someone knows this device?Thanks a lot for your support. I am not convinced that I would had fix this issue without your help. It would had take a lot of time.

author: tom66
author_rank: Super Contributor
timestamp: March 29, 2025, 11:24:02 am
content: That's probably the DAC for the channel offsets.Something like (but probably not exactly) this -https://www.analog.com/media/en/technical-documentation/data-sheets/AD5337_5338_5339.pdfWith the DAC being bad, the ADC inputs would be out of range for most inputs.Good fix, strange how that solder ended up there?!

author: Swake
author_rank: Frequent Contributor
timestamp: March 29, 2025, 05:09:58 pm
content: Good catch, happy you found that drop of solder.Another device saved from the dumpster!

author: tautech
author_rank: Super Contributor
timestamp: March 29, 2025, 08:34:42 pm
content: Quote from: tom66 on March 29, 2025, 11:24:02 amYep, the DEX package mark had me searching for quite a while with zero hits but at least the one you linked above had D** markings for all the variants.Certainly close.....The solder ball had missed QC at Siglent's PCB supplier as it's unlikely to have got to the middle of the scope any other way.It's a shame jfcen29 didn't capture a pic of it.....

author: tom66
author_rank: Super Contributor
timestamp: March 29, 2025, 10:49:00 pm
content: What's weird is how it wasn't an issue until recently.

author: tautech
author_rank: Super Contributor
timestamp: March 30, 2025, 02:47:29 am
content: Quote from: tom66 on March 29, 2025, 10:49:00 pmSorta is but a positional change, bump or higher humidity might have started the stray solder to conduct, partially or wholly where it hadn't been a problem before. Maybe some flux trapped it initially, who knows ?Faults and fixes like these are always interesting and determining the absolute cause not always possible but we should all bask in the glory of helping to fix another instrument.