ATTN: Micsig handheld scope owners with DC offset instability issues

[Fraser]

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

[nctnico]

It seems these are sold by a Micsig dealer on Ebay.

[Fraser]

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

[eKretz]

It seems these are sold by a Micsig dealer on Ebay.

Yep, 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?

[Muttley Snickers]

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.

[nctnico]

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.

[cdev]

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 is not simply remarkably sensitive and is measuring 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.

[Fraser]

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

[cdev]

Flux contamination could likely do something similar too, I think.

[mtdoc]

But regardless, ekretz, even if your scope is not simply remarkably sensitive and is measuring 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.

Good 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.

[TheAmmoniacal]

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.

[TheAmmoniacal]

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?

[TheAmmoniacal]

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

Will you tell us how to get the official MS220T firmware onto this debranded model? 

[eKretz]

The eBay seller IS Micsig. I did take the problem up with the eBay seller, who referred me 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 an employee of 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.

[cdev]

The Micsig people aren't native English speakers so probably what they meant was that if you had bought a branded Micsig product then you 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.

[eKretz]

Yes, I clearly must be an idiot.

From the eBay seller:

Hi dear, we just receive your message, but quite can't figure out your issue, would mind send a video to our email, so we can solve it clearly, thank u.
europe@micsig.com
Jelin Wei

Skype? Jelinwei

Shenshen Micsig instruments Co., Ltd.

www.micsig.com

And $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.

[TheSteve]

The Micsig people aren't native English speakers so probably what they meant was that if you had bought a branded Micsig product then you 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.

The price is really irrelevant, they were sold as working scopes by Micsig.

[TheAmmoniacal]

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.

[eKretz]

Again, I was referred back to Micsig BY the 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.

[eKretz]

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.

[Fraser]

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

[eKretz]

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 conditions  but I'll leave this thread as it is for anyone else who might run into this issue.

[tautech]

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 ? 

[eKretz]

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.

[tautech]

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.................

My turn:
Haha, right?

But they do look interesting.