ATTN: Micsig handheld scope owners with DC offset instability issues - Page 1
Forum section: electronics / testgear

author: eKretz
author_rank: Frequent Contributor
timestamp: January 07, 2017, 08:20:28 am
content: Hiya fellas, recently picked up a discounted handheld scope on fleabay - posted in this thread:https://www.eevblog.com/forum/testgear/debranded-micsig-handheld-scope-on-sale-on-ebay/and am having some issues with the DC offset wandering around. My bench scope doesn't do anything like this - I'm wondering if this is something I should be worried about enough to request a replacement - the seller is trying to play it down.Quick video:http://s240.photobucket.com/user/eKretz/media/Pub/TRIM_20161231_013516.mp4.htmlOn the 20mV/division range, the zero floats around nearly 8mV. Makes it tough to get a cursor measurement unless the acquisition is stopped - but then I have to wonder if it stopped anywhere near where it should be. This occurs with no probe attached as well as with a signal on screen. Higher ranges jump about the same percentage of the range. The range is way higher than the claimed 2% DC accuracy. Contacted the seller and was told I was using the trigger wrong? I think they are making excuses.Edit: I believe this issue has been resolved - there appear to be damaged or faulty LM6518 ICs. See page 2 for further detail.

author: mzacharias
author_rank: Frequent Contributor
timestamp: January 07, 2017, 10:26:52 pm
content: And it does this with probes shorted or the AC/DC coupling switch set to "ground" ?

author: eKretz
author_rank: Frequent Contributor
timestamp: January 08, 2017, 07:54:30 am
content: Less with the coupling set to ground coupled, that cuts it down quite a lot though still visibly jumping around a bit even then, but yes just as bad with a probe connected and grounded. And that is with even good quality probes, not the cheapies supplied with the scopemeter.

author: mzacharias
author_rank: Frequent Contributor
timestamp: January 08, 2017, 01:29:58 pm
content: I'm not sure I would expect a handheld digital scope to maintain a flat trace with no signal. DAC noise alone probably would account for this, unless it's really bad. My experience is exclusively with analog scopes however, so others will have to advise you on this.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 09, 2017, 05:26:59 am
content: Well I'm not really expecting a flat trace, but this seems like an erratic thing. It will be mostly okay for a few seconds, then bam! A jump upwards or downwards for a few seconds, then bam! A jump in the opposite direction.This is definitely worse in the first two division settings of each range before the relay can be heard switching to a higher voltage setting range. In other words, the lowest setting of 20mV/division is bad, and so is the next one, then it's a good bit better until range is increased to 1V/division - at which point the relay can be heard switching to that setting range. Then it's awful again for 1V/division and 2V/division, then a little better until the relay switches range again.At 1V/division with a ~2.1V RMS (~6V P to P) 60Hz sine wave, the mean voltage is jumping around 400+mV erratically. My bench scope with the exact same settings is staying within 4mV, and is WAY more stable. I could totally understand a little bit more wander in a handheld scope - but this seems hugely excessive to me - especially when some ranges are way better than others and the scope is rated at 2% DC offset accuracy.

author: Howardlong
author_rank: Super Contributor
timestamp: January 09, 2017, 12:17:40 pm
content: The tablet Micsig I have doesn't seem to have this behaviour, it's rock steady with a 2.1V RMS 60Hz sine input from a signal generator, and both mean and cmean measurements hovering around 2mV.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 09, 2017, 04:27:49 pm
content: Thanks, I appreciate you checking in. I got an idea from another member to tie both scopes together with a BNC adapter so I can show that it is specifically the handheld that is having the issue. I'll make a video of that today.

author: mtdoc
author_rank: Super Contributor
timestamp: January 09, 2017, 09:00:18 pm
content: I do not have that much wander on my ebay debranded Micsig handheld.With grounded probe or no probe attached, 10x probe setting, 20mV/div, DC coupling, I get about 2 mV of wander at most - which is well within the 2% spec (which would be 3.2 mV at that setting).If I first ground the input coupling (which drops the wander to about 0.1 mV) then go back to DC coupling, the wander is only about 1 mV.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 09, 2017, 10:42:33 pm
content: Thank you for the input mtdoc! I had a feeling this was quite abnormal. Just watching a trace on the display - it can be seen jumping around quite erratically. Sometimes I also see it make a huge jump on screen but it's between measurement updates (measurements only seem to update once a second or so) so it doesn't register.I made a video today of the handheld and my bench scope side by side during which I run the handheld through calibration and then feed the same signal into both scopes; then within less than a minute the mean voltage is jumping around over 200mV on the handheld. On the bench scope it's staying steady within 6mV. I'll post that tonight.If they don't decide to replace this one after this video I guess I'll have to instigate something with eBay.

author: nctnico
author_rank: Super Contributor
timestamp: January 10, 2017, 12:37:33 am
content: If you bought it through Ebay then open a case immediately! Only then can you elevate a case to a claim/refund if necessary. Don't ever wait for a seller to replace a product because the moment you find out the seller isn't going to replace or refund the period you can file a claim is passed.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 10, 2017, 01:47:59 am
content: Good advice actually, I just did that. I'm not particularly happy with the first response, already making excuses. I have had this unit for barely a week and they are already claiming I have had it over a month.It's a shame really, I would really quite like it if it worked correctly.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 10, 2017, 07:51:25 pm
content: Okay, here's the video of both scopes fed the same signal at the same time. All settings are either the same or as close as they can be (timebases aren't exactly the same, but as close as I could get). I let both scopes warm up for an hour before doing the calibration on the handheld. Within a minute after the calibration the mean has wandered above and below zero to around a 200mV range at the 1V/division setting with ~6V peak to peak 60Hz sine wave. Both scopes DC coupled and at their full bandwidths, no averaging.https://youtu.be/Vs3TblDIWMs

author: nctnico
author_rank: Super Contributor
timestamp: January 10, 2017, 08:02:43 pm
content: Why does it say 'scope is adjusting...' in the screen? Do you have some automatic signal/trigger setup enabled?

author: eKretz
author_rank: Frequent Contributor
timestamp: January 10, 2017, 08:09:20 pm
content: That's the self calibration. The procedure is to remove the probe(s) then perform the calibration. In the video I start calibration, then it self adjusts/calibrates, then I plug the BNC back in with the same signal going to both scopes. So this jumping around DC offset instability is immediately after the calibration. It only gets worse with more time.

author: nctnico
author_rank: Super Contributor
timestamp: January 10, 2017, 08:29:09 pm
content: Does the signal also wander around without the probe connected (nothing connected to the oscilloscope's BNC input)? That is not clear from the video. You need to make a clear distinction whether the problem is in the oscilloscope or the probe/cable.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 10, 2017, 08:36:10 pm
content: Yes it does the exact same thing with no probe attached and I've already sent them a video of that as well. Here is a short vid of the scope with no probes attached - this is in the 20mV/div range though.http://s240.photobucket.com/user/eKretz/media/Pub/TRIM_20161231_013516.mp4.html

author: nctnico
author_rank: Super Contributor
timestamp: January 10, 2017, 08:48:50 pm
content: In that case it is broken and should be replaced.

author: mtdoc
author_rank: Super Contributor
timestamp: January 10, 2017, 10:08:15 pm
content: Quote from: eKretz on January 10, 2017, 07:51:25 pmWith the same signal, my debranded Micsig portable shows no visually apparent movement - and the measured mean wanders by only 2-3 mV. This is true without a prior self calibrate. Interestingly, if I do a self calibrate immediately prior, the measured mean wanders by a bit more, about 30mv - but this still not visually apparent at that scale. The mean does sit at about -200mV if DC coupled, but that's no bother.eKretz - it would probably help your case if you submitted a less blurry video. It's hard to make out the readings on the scopes. You should probably also pan back at some point to show your cabling set up.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 11, 2017, 12:17:00 am
content: I had a hard time getting the camera to focus any better - I don't have anything but my cell phone to take video. I can read the on-screen numbers when I view it anyway. I don't have any good means of uploading either. My home internet is awful, I have to make a special trip to upload video - and although I understand my videos aren't professional quality (more like kid-level) they should be plenty good enough to see what's going on. I also was trying my darnedest to keep the videos as short and small as possible so I had some chance at uploading them without spending hours borrowing someone else's internet connection. I am disabled so not able to afford better internet ATM - that also makes it hard for me to get out of the house on a lot days.If my scope sat steadily, I wouldn't give a darn about a slight offset within spec, but the jumping all around is a different story. And after calibration mine is at its best - if I made a longer video it would get up closer to 400mV difference from the high to low mean voltage.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 11, 2017, 02:44:35 am
content: Well, looks like there are trying to screw me over. Here's the reply I just got:QuoteCan some of you other guys post a video of yours showing they aren't doing this? Unbelievable.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 11, 2017, 07:32:50 am
content: I guess if you want a REAL scope don't buy Micsig, they pretty much said it themselves. I can't believe they are asking for videos of other peoples' scopes as proof. Considering they listed this scope as "fully functional" except for having disabled the multimeter function I am very disappointed.You guys that don't have this issue on your Micsig please help me out! I need videos to refute their BS.

author: TheSteve
author_rank: Unknown
timestamp: January 11, 2017, 07:47:52 am
content: I suspect you'll need to file an ebay/paypal dispute with them. Before you do I would contact them at least once more and give them the option to replace it or refund your money as it is defective. Let them know you will file a dispute if they do not resolve the issue as it is defective.

author: Micsig_support
author_rank: Regular Contributor
timestamp: January 11, 2017, 10:34:02 am
content: Dear eKretz,We are sorry to hear this. But this is not the Micsig products, can you contact the seller to solve your problems? And we also suggest you to contact them to return your products.Micsig always try to provide the best products and services to our customers. if you have any question with Micisg products, and you can email to america@micsig.com or sales@micsig.com, we will reply you very soon.Micsig technical support

author: BravoV
author_rank: Super Contributor
timestamp: January 11, 2017, 10:41:31 am
content: Hmm .. I thought all this time its a Migsig brand ?eKretz, whats the brand anyway ?

author: eKretz
author_rank: Frequent Contributor
timestamp: January 11, 2017, 11:07:16 am
content: It's "debranded" (name label removed) but of course it's sold by the Micsig factory eBay seller and when I initially complained about the problem they referred me to a Micsig email address - from which I got the above quoted message. So I don't know - you tell me what brand it is. It's just more dishonest/weaselly behavior as far I'm concerned.Now since I just added the name Micsig they are all of a sudden much more conciliatory. Except now they are asking me to pay to ship the thing back on my dime rather than replacing it or issuing a prepaid label for the shipping of the defective item - which ain't gonna happen.

author: Fraser
author_rank: Super Contributor
timestamp: January 11, 2017, 11:12:12 am
content: Hmmmm just read the latest in this thread.It reads like the eBay seller is not selling approved Micsig products and maybe selling factory rejects. This is always a risk when buying so called "debranded" products. In truth, they were never branded and were production line rejects that should be scrapped.Has some clever trader somehow got their paws on a pile of scrap scopes I wonder ? If so, they could contain more faults than just the multimeter section.I was surprised when I first read of the "debranded" Micsig scopes. Most manufacturers will not sell sub standard or partially faulty equipment as it can damage their brand. I know the name may have been removed but these are easily identified by appearance. Alternatively, someone at Micsig may have got overly creative and thought selling partially faulty kit was a good idea. They may live to regret that decision.Fraser

author: nctnico
author_rank: Super Contributor
timestamp: January 11, 2017, 11:25:33 am
content: It seems these are sold by a Micsig dealer on Ebay.

author: Fraser
author_rank: Super Contributor
timestamp: January 11, 2017, 12:06:00 pm
content: Just saw that they are willing to accept return at buyers cost.This is not unusual as many China sellers offer only a RTB warranty.I believe under eBay terms of sale, faulty items are returned at the sellers cost via either prepaid returns label or postage payment to the buyers PayPal account. You may never see the scope again though as such returns often go "missing" in transit. Lots of hassle ahead I fear.I would raise an eBay returns case as already stated and never return such an item without insured and tracked shipping or eBay will not cover you for loss.Alternatively, consider how much you paid for this portable DSO, whether the low range drift is truly a real world issue for you and whether you can live with it. Some users would not have a problem with such a signal offset deviation. Such may well be inherent in the design, with some scopes suffering from it more than others. If you cannot live with it, I suggest a return and refund is the better option than a repair or exchange unit. Debranded kit does not normally have much, if any, support. That is why it is cheap (no support costs for seller)If such is not explicitly stated in the auction, eBay will support your case.Fraser

author: eKretz
author_rank: Frequent Contributor
timestamp: January 11, 2017, 01:01:54 pm
content: Quote from: nctnico on January 11, 2017, 11:25:33 amYep, and although they scratched the brand name off, from the first that I've been in contact with the eBay seller they immediately referred me to "their engineer" which is a Micsig domain email address. The listing started "fully functional oscilloscope" with "closed multimeter," however that translates.Honestly at this point I guess I would rather just send it back if it wont ever be right and look for a used reliable/reputable brand handheld in the future. If it worked I would keep it. Now you've got me worried about whether they will even admit they received it. I wonder is there a way to make sure they send a tracked/insured prepaid label?

author: Muttley Snickers
author_rank: Unknown
timestamp: January 11, 2017, 01:36:49 pm
content: I don't know what the Ebay/ Paypal policy is elsewhere and half the time I wonder if they really know themselves, anyway, Hobby King tried to shaft me on a purchase and to claim full reimbursement of the initial order I was required to return the small parts that did turn up back to Hong Kong even though they were originally sent to me from Sydney NSW. Paypal required me to pay the registered return shipping which was five times the value of the items and forward a copy of the registered post confirmation receipt which was provided by the post office where I submitted the items. It didn't matter that the goods were or weren't received their end only that I provided documented proof my end that they had been sent. Eventually the items I sent came back anyway as the address that Hobby King provided to Paypal was a bullshit address which was confirmed in writing by HK Post.Unfortunately these types of episodes can be somewhat distressing at times, fingers crossed and best of luck.

author: nctnico
author_rank: Super Contributor
timestamp: January 11, 2017, 01:54:18 pm
content: I'd read Ebay's/Paypal's terms carefully. IIRC some items are covered by a warranty where Ebay or Paypal pays the return shipping.

author: cdev
author_rank: Super Contributor
timestamp: January 11, 2017, 03:52:19 pm
content: Is there any chance its just the high input impedance? The DC offset issue you're describing sounds to me like it could be explained by high input sensitivity.Please excuse me if you already eliminated this possibility but - on the off chance you havent- some people might not realize that these voltages are always there..If you do simple experiments with high gain op amps and FETs (with very high input impedances) you realize quickly that there are varying voltages on everything all the time, and they change a lot. Anything that is (well) insulated from the ground will collect charges. Especially when the humidity is very low!You know, the ESD we are familiar with -But regardless, ekretz, even if your scope isnotsimply remarkably sensitive and ismeasuring ESD for you, please step back and take a breath and look at the comparable products out there at that price, and the discussions about them in other threads, to get a broader perspective on the situation before jumping to negative conclusions.certainly some vendors sell crap products, but this one does not seem to qualify as one under any definition of that term. Instead they made a remarkably high quality product available at a very low price.My old Tek 2211 scope has a very high sensitivity input setting (its one of only a very few Tek models that do) and when its set to that range, sometimes it also picks up DC in the air, when its very dry. It has nothing wrong with it.Although the humidity today seems much higher than it was a few days ago (when I was testing a power supply I was fixing.) when I last observed this. I can usually tell when there is a lot of static electricity in the air from the amount of little sparks I hear when I touch things, put on a woolen sweater, etc.You can also set up a simple circuit to measure it using a single FET. If you go to Techlib.com there is a wealth of circuits for things like a "Ghost Detector" which act as sensitive electrostatic field detectors.A few years down the line, you might in retrospect wish you had eliminated that possibility before you returned what may be an above-average acquisition.Please disregard my comment if you have already eliminated this possibility.But since non-deterministic behavior in electronics is unusual, I think its not unlikely that its measuring something real, and it seems likely that ESD is it.

author: Fraser
author_rank: Super Contributor
timestamp: January 11, 2017, 03:59:18 pm
content: In the other thread about these scopes an owner states that his wandering offset problem appears to have been caused by too much flux contamination around certain IC's. Worth a look ?Fraser

author: cdev
author_rank: Super Contributor
timestamp: January 11, 2017, 04:27:56 pm
content: Flux contamination could likely do something similar too, I think.

author: mtdoc
author_rank: Super Contributor
timestamp: January 11, 2017, 06:34:44 pm
content: Quote from: cdev on January 11, 2017, 03:52:19 pmGood advice. Remember that these units are being sold at about 1/5 the price of a branded unit with at least one known and declared defect. Caveat emptor buying anything like this on eBay. There is always some risk assumed with these deals which is justified by the low price. Yes, with some effort you can probably leverage eBay's policies to get a full refund including shipping but in the meantime I would try to keep some perspective. You did not buy a branded Micsig scope from an authorized Micsig dealer. It's not fair IMHO to expect the same level of customer service as if you had or to direct your frustration at Micsig.

author: TheAmmoniacal
author_rank: Unknown
timestamp: January 11, 2017, 07:10:11 pm
content: Involving Micsig in this is not fair, this is entirely between you and the eBay seller. The eBay seller clearly says the scope is working "as normal", if it does not you take it up with him. Replacement unit, partial or full refund.I have the exact same "debranded" scope, will take a look at it.

author: TheAmmoniacal
author_rank: Unknown
timestamp: January 11, 2017, 07:31:43 pm
content: Can't see any abnormal behaviour on mine, my mean only change by 2 mV.1. What happens if you click Autoset?2. What is the T <- 50x -> setting I see on your scope?3. How you tried to factory reset it?

author: TheAmmoniacal
author_rank: Unknown
timestamp: January 11, 2017, 10:20:17 pm
content: Quote from: Micsig_support on January 11, 2017, 10:34:02 amWill you tell us how to get the official MS220T firmware onto this debranded model?

author: eKretz
author_rank: Frequent Contributor
timestamp: January 12, 2017, 04:16:13 am
content: The eBay seller IS Micsig. Ididtake the problem up with the eBay seller, whoreferredme to Micsig! They apparently are selling the scopes that don't pass QC or that need rework through this eBay seller, who is pretty apparently anemployeeof Micsig from the emails I've received, directing me to email Europe 'at' Micsig.com to further discuss the problem with "his" engineer, because the seller is just sales personnel. The same seller is selling all the new Micsig branded scopes as well.The stray/ESD voltage thought is interesting, but if that were the case, why does this happen in the 1V/div range and higher as well? And not happen on my Tek scope (500MHz, tweaked to 1GHz now) sitting right next to it? And also hasn't happened in any other scope I've ever used? Both scopes are also sitting on top of an ESD safe mat that is grounded. It's pretty clear that this is an issue with some of the scopes and not others.Having just taken a look inside the analog front end, I can see definite evidence of rework - lots of leftover flux from hand soldering all over the place on what I think are opamps. I'm going to give the cleaning procedure posted by rpress from the other thread a try tonight and see if that rectifies it.

author: cdev
author_rank: Super Contributor
timestamp: January 12, 2017, 04:54:15 am
content: The Micsig people aren't native English speakers so probably what they meant was thatifyou had bought a branded Micsig productthenyou would deserve high level Micsig support -Look, the fact is, you spent $200 on the thing...That said, if you see a lot of flux, its quite possible you could improve things by cleaning it better, but also you should read the ongoing thread about flux removal first and keep in mind that some kinds of removal may not work as well as you think. With some fluxes and some cleaners (like IPA) you could easily make it worse.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 12, 2017, 05:16:41 am
content: Yes, I clearly must be an idiot.From theeBay seller:QuoteAnd $200 may be like pennies to you, but being on a fixed income it is significant to me. I expected to receive a functional scope without defects, as stated in the listing. If the accuracy was just off, it wouldn't be a big deal, but jumping around erratically is not good, and for all I know could be an indication of some IC about to fail.

author: TheSteve
author_rank: Unknown
timestamp: January 12, 2017, 05:48:21 am
content: Quote from: cdev on January 12, 2017, 04:54:15 amThe price is really irrelevant, they were sold as working scopes by Micsig.

author: TheAmmoniacal
author_rank: Unknown
timestamp: January 12, 2017, 06:38:32 am
content: The fact that this scope is made by Micsig is not up for debate, that's obvious. It's also obvious that the scope is not sold as a Micsig, and that it does not come with Micsig warranty.This is a dispute between you and jelinwei (the eBay seller, not as the Micsig employee).1. Threaten him with negative feedback, say the item is not the same as described.2. Open a case on eBay.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 12, 2017, 07:07:36 am
content: Again, I was referred back to MicsigBYthe seller. I had no choice but to open a dialog with Micsig, who were trying to tell me there is not a problem with the scope.Micsig have finally offered to take a return with them paying the shipping today. I am going to take a crack at cleaning the flux residue first. If that doesn't work, I will probably take the return offer. In the meantime, other potential buyers should beware. IMO a reputable company would replace the defective item rather than take a return, but whatever.

author: eKretz
author_rank: Frequent Contributor
timestamp: January 16, 2017, 06:58:32 am
content: Okay I attempted to clean the front end components with a stiff brush and alcohol - cleaned everything up as well as I could and found no difference in the offset instability.After seeing a post by rpress in the handheld scope thread I decided to remove the ICs in the AFE and clean under them and try swapping them to see if the instability followed the components from channel to channel. I swapped the AD706s and OPA4872s and cleaned thoroughly again. Again there was no change - the problem was still mainly on channel 1 - slightly there on Channel 2 but not nearly as bad.Next I tried swapping the WQFN ICs - the LM6518s - and again cleaning thoroughly. After swapping these, Channel 1 was much better and Channel 2 was much worse - so the problem followed the LM6518s. I guess either the 6518s are faulty or were damaged at some point - or maybe counterfeit ICs? No idea.After this discovery I contacted the seller again and offered to drop the return request in exchange for a partial refund that will cover the purchase of replacement LM6518s and $10 for the faulty probe that was sold with my scope. They accepted the offer so I guess this is resolved to my satisfaction.

author: Fraser
author_rank: Super Contributor
timestamp: January 16, 2017, 07:16:02 am
content: Good news. I am very pleased for you. It is fortunate that you have the required skills to replace the faulty component. All is well that ends well.Fraser

author: eKretz
author_rank: Frequent Contributor
timestamp: January 16, 2017, 07:57:05 am
content: Yup, thanks. I'm definitely glad to have found the issue finally.Thanks goes to rpress for giving me some inspiration and ideas on where to look as well. After this is sorted I will be quite happy with this bit of kit. Still not very happy that they tried to pass this off as normal operating conditionsbut I'll leave this thread as it is for anyone else who might run into this issue.

author: tautech
author_rank: Super Contributor
timestamp: January 16, 2017, 08:05:56 am
content: Seems weird that the factory QC identifies these as not fit to wear their brand and they dump them on the market rather than repair them.As Micsig are members here they'll no doubt spot your fix and there might be less of these units available in the future.Maybe you should send them a bill for fault diagnosis ?

author: eKretz
author_rank: Frequent Contributor
timestamp: January 16, 2017, 08:12:56 am
content: Haha, right? Apparently the scope part of the meter is supposed to be fully functional - the faulty bit that caused them to "debrand" the units is supposed to be the multimeter - but most of the guys who posted in the other thread were able to restore the multimeter function also and don't seem to be finding any huge problems with it.Although you'd think it would be cheaper to repair them for sure, considering how much more the functional branded ones sell for.

author: tautech
author_rank: Super Contributor
timestamp: January 16, 2017, 08:32:21 am
content: Quote from: eKretz on January 16, 2017, 08:12:56 amMy turn:Haha, right?But they do look interesting.