New uCurrent offset way out of spec (-6mV!) - Page 1
Forum section: electronics / testgear

author: Insatman
author_rank: Frequent Contributor
timestamp: January 12, 2018, 05:57:34 am
content: I just received a new uCurrent Gold today and thought I'd give it a little test. The unit has a fresh battery (CR2032) and has never seen over 50mA input on it's mA range. I am measuring millivolts of offset without any current input as opposed to the spec of <50uV. Shorting the input makes no difference. I tried three different meters and got the same result. The offset voltage is a bit less on the nA range, but unchanged on the uA range. See photos. Note if I use the null feature on the multimeter and apply my precision 50mA source I will get a reading of around 49.5mV. So the op-amps are working but the accuracy is out of spec as well.

author: keox
author_rank: Newbie
timestamp: February 04, 2018, 09:29:51 pm
content: Hi, I just got my uCurrent Gold v5 serial no: 5153 and also observe an offset of the output voltage. Did you sort out the problem?There is a dependency between an offset of the output voltage and supplied battery voltage (all measured in 1mV/mA range, all tests were with done without any current input):Batt voltage: 2.7V (close to batt ok cut off), offset: -5.8mV3.0V -> -4.9mV3.5V -> -3.7mV4.0V -> -2.8mV4.5V -> -2.4mV5.0V -> -2.1mVI did not go beyond 5.0V

author: Insatman
author_rank: Frequent Contributor
timestamp: February 05, 2018, 02:20:07 am
content: Quote from: keox on February 04, 2018, 09:29:51 pmI have not sorted out the problem. I did some measurements and determined that the offset is from the last op-amp in the chain. I have made 4 attempts to email Dave Jones with the data and have had no response (can you hear crickets?). I also sent him 3 private messages on this Forum...again no response.I have not been able to find any link on his webstore to report problems, so I tried emailing. I am very dissappointed in Dave's customer service at this point. He (or his workers) were quick to process my order and the unit arrived fairly quickly, but ZERO response to my attempts to get this resolved.I have purchased a replacement op-amp but have not yet touched the board in the hope that Dave contacts me.I am not surprised that the offset is battery voltage related.

author: keox
author_rank: Newbie
timestamp: February 05, 2018, 05:43:20 am
content: I PMd Dave and hope he will chime in.Meanwhile, how did you find the culprit? Can you pls help me to find mine? I am a newbie to electronics, but not a newbie in CS, if it will help..

author: EEVblog
author_rank: Unknown
timestamp: February 05, 2018, 07:25:41 am
content: We are investigating this now.

author: EEVblog
author_rank: Unknown
timestamp: February 09, 2018, 05:58:33 am
content: Solved!

author: imidis
author_rank: Frequent Contributor
timestamp: February 09, 2018, 06:59:51 am
content: Why is this not (video) showing under my subscriptions? Is it unlisted?

author: BU508A
author_rank: Super Contributor
timestamp: February 09, 2018, 07:20:18 am
content: Quote from: EEVblog on February 09, 2018, 05:58:33 amAnd now for the new batch you have to replace all these OpAmps?Lot of work, though ...

author: imidis
author_rank: Frequent Contributor
timestamp: February 09, 2018, 07:38:30 am
content: Ah good point!

author: EEVblog
author_rank: Unknown
timestamp: February 09, 2018, 07:49:59 am
content: Quote from: imidis on February 09, 2018, 06:59:51 amYes. I released it early to Patrons, so unlisted. And it's best to release videos in the morning (my time) to catch the most people at the best time.

author: EEVblog
author_rank: Unknown
timestamp: February 09, 2018, 07:50:38 am
content: Quote from: blueskull on February 09, 2018, 07:21:43 amI should do that but I suck at it.

author: Insatman
author_rank: Frequent Contributor
timestamp: February 09, 2018, 11:24:57 am
content: I used a piece of coax and two banana jack adapters between the uCurrent and all three meters I tested when I did my original measurements. Looks like the coax capacitance and the bad op-amp was the culprit. Ironically, I used a coax so the measurement would have less noise...lol.

author: Thetatronics
author_rank: Newbie
timestamp: February 09, 2018, 03:10:30 pm
content: When will there be a new batch of the uCurrent Gold available in your shop? I could really use it for a contract I'm picking up in the next couple of weeks.

author: Simon
author_rank: Unknown
timestamp: February 09, 2018, 05:07:00 pm
content: I have one but the chip that does the battery monitoring is missing. I have ordered some from Texas instruments and am still waiting for them to arrive but assumed I have them it should be as good as new. I'll be setting up my shop again shortly now that I have moved so and decided which particular control panel I want running my new cloud server. If that helps you out.

author: Thetatronics
author_rank: Newbie
timestamp: February 09, 2018, 06:54:52 pm
content: Yes I would be very interested in purchasing it. Please let me know when your shop is back up and I'll order it ASAP. Do you know whether your boards have the same dodgy part that Dave found in his video?

author: Simon
author_rank: Unknown
timestamp: February 09, 2018, 07:20:21 pm
content: it probably does as its out of the last batch , well serial 004706

author: blackdog
author_rank: Frequent Contributor
timestamp: February 09, 2018, 08:41:19 pm
content: Hi,I think the feedback capacitor of the last opamp should be connected to the opamp output en NOT to the output connector...Kind regarts,Blackdog

author: Insatman
author_rank: Frequent Contributor
timestamp: February 13, 2018, 06:52:50 am
content: Yesterday the recommended replacement IC for the split-ground op-amp arrived from Digikey (LMV321IDBVR from TI). I viewed Dave's two videos on EEV on doing a fix which does not involve replacing the op-amp but both methods have their drawbacks. So I replaced the IC in question this morning and ran several tests afterward. My offset voltages are now <100uV using shielded-twisted pair or coaxial hookup. The offsets are a bit larger with bare leads at times likely due to noise pickup. I'm not great at surface mount soldering but managed it anyway. The IC costs less than $1, so I just piggybacked it onto my next Digikey order. I recommend you go this route if you can get the IC easily.

author: jeremy
author_rank: Super Contributor
timestamp: February 13, 2018, 07:12:53 am
content: What I learned from this video: if you need to debug a basic op amp design, better have 4 kidneys worth of test equipmentInteresting video!

author: Insatman
author_rank: Frequent Contributor
timestamp: February 13, 2018, 08:46:42 am
content: Quote from: jeremy on February 13, 2018, 07:12:53 amSold off kidneys of all my family and several neighbors...lol...but at least I have test equipment...

author: EEVblog
author_rank: Unknown
timestamp: February 13, 2018, 09:24:49 am
content: Quote from: Thetatronics on February 09, 2018, 03:10:30 pmNew opamps are on the Digikey truck now to the assembler

author: tcottle
author_rank: Contributor
timestamp: February 13, 2018, 06:34:11 pm
content: After watching the video last night I checked my brand new uCurrent Gold this morning. S/N 5199 and U2 is 321TI am also going down the "piggyback onto my next Digikey order" repair route. Here is the link for the lazy:https://www.digikey.com/product-detail/en/texas-instruments/LMV321IDBVR/296-9567-1-ND

author: lapse
author_rank: Newbie
timestamp: February 20, 2018, 03:57:24 pm
content: I have (had) a uCurrent with the 321T. I received a LMV321IDBVR from Digikey and replaced the 321T. I'm still reading an offset on my Fluke 15B+ in the mV scale with nothing on the current input.Without a capacitor across the output:OFF->nA/uA/mA->0.0mVON->nA->0.0mV, ON->uA->-0.2mV, ON->mA->-0.2mVSHORT->nA->-0.8mV, SHORT->uA->-0.3mV, SHORT->mA->-0.2mVWith a capacitor across the output:OFF->nA/uA/mA->0.0mVON->nA->0.0mV, ON->uA->-0.1mV, ON->mA->-0.2mVSHORT->nA->-0.5mV, SHORT->uA->-0.1mV, SHORT->mA->-0.1mV

author: Lightages
author_rank: Unknown
timestamp: February 20, 2018, 05:05:49 pm
content: I am confused or missed something. The uCurrent Gold has a manufacturing flaw that some customers have received. Is there no warranty? The customer needs to fix the problem him/herself? I must have missed something.

author: rsjsouza
author_rank: Super Contributor
timestamp: February 20, 2018, 05:55:41 pm
content: Playing devil's advocate: I don't see warranty terms on the purchase page - buy at your own risk.On the other hand, perhaps Dave is giving some sort of compensation via other means. I don't know, as I haven't purchased one from this new batch - I have an older generation.

author: Insatman
author_rank: Frequent Contributor
timestamp: February 21, 2018, 12:03:54 am
content: Quote from: Lightages on February 20, 2018, 05:05:49 pmHi..original author of the post here... I have written Dave four emails on this subject with ZERO response. When the first person responded with a simular problem Dave did PM us, telling us he verified the problem and later told us about the op-amp and that he would post a video. No offer of replacement or repair was given at that time.In the video he says something like "if you have one of these contact me and we'll work something out". After that I PM'd Dave again and got NO response. Another member also PM'd him and sent me a copy. NO response to our shared PM thread.In total I have emailed Dave four times and PM'd him about four additional times asking what he proposed to do. I got no response. I don't have a problem with the fact that a fault occurred. These things happen in tech. What upsets me is the lack of response from Dave. His organization was quick to process my order, but is completely unresponsive when I point out a problem, other than to issue a video describing the problem and issuing a kinda weak empty promise at the end of "working something out". If Dave has simply written me and asked if I would mind replacing the IC myself, I would not have felt the need to write this post. Just some response indicating that he stands behind his product.I can only conclude that customer service on this product is non-existent other than verifying the problem and proposing how it can be repaired by the user. The promise of "we'll work something out" appears to be empty...although I hope to be pleasantly surprised by Dave I'm not hold my breath. I went ahead and repaired my unit by replacement of the op-amp.The product itself is decent....I had assumed that Dave would be responsive to his customers....I was wrong...

author: thm_w
author_rank: Super Contributor
timestamp: February 21, 2018, 12:12:36 am
content: With the multimeter now/shortly to be released, maybe a eevblogstore or support@eevblog email address is deserved.

author: Insatman
author_rank: Frequent Contributor
timestamp: February 21, 2018, 12:39:20 am
content: Quote from: thm_w on February 21, 2018, 12:12:36 amProvided that it is actually responded too, that would be a great step in the right direction.

author: Insatman
author_rank: Frequent Contributor
timestamp: February 21, 2018, 03:42:08 am
content: Quote from: Insatman on February 21, 2018, 12:03:54 amWell...I am pleasantly surprised after all as Dave just responded to one of my emails this morning. It took awhile but...Apparently I was proven wrong about being wrong...lol...I won't quote his email but he did offer to make things right. I stand corrected on this matter.

author: tautech
author_rank: Super Contributor
timestamp: February 21, 2018, 06:06:46 am
content: Quote from: Insatman on February 21, 2018, 03:42:08 amThere are ways to get Dave's attention when it'simportantto do so and I was about to use this quite straightforward trick until I read this last post.Anyways, use the 'Report to Moderator' button and add a quick comment for Dave to contact the member.Often he won't see it but when Simon does he'll let Dave know.Dave's got a lot going on.............

author: Simon
author_rank: Unknown
timestamp: February 21, 2018, 07:51:08 am
content: I think the problem is still being investigated to find a robust solution. Dave did say to get in touch if you have one and he'd sort it out.

author: EEVblog
author_rank: Unknown
timestamp: February 21, 2018, 08:08:00 am
content: For those curious about why I didn't respond to initial emails about this, there are two reasons:a) I get a lot of emailbut more to the pointb) I get a lot of email about the uCurrent and how to use it etc, and in almost every case it's people having no idea how to use it, their setup is wrong, etc etc. Genuine hardware faults are incredibly rare.andc) It takes a lot of time to investigate and actually respond to emails like this, so unless it's a one-liner response I often leave it unread to deal with later. I know this sounds shitty, but I have a finite number of hours in my life. And I'm not going to respond with "I'm working on it" if I'm not actually working on it.So when I see an email about an offset problem like this, for very genuine reasons I didn't think it could possibly be the hardware, it was most likely yet another user setup problem that will take ages to solve. Then when I actually tested a current batch one, it tested fine, so what was I to do right away?It's only when I saw the 2nd report on the forum that I really jumped on it and knew something was up and investigated straight away.This of course turned out to be a very rare and obscure fault that was not immediately obvious. Obvious with hindsight of course.