uCurrent Gold Dead Out-of-Box?

[beaker353]

With must anticipation, I got my uCurrent Gold #1074 today in the mail. However, I think I may have gotten a dud.

With the input completely floating, I get 1.36V on the output on all ranges powered from either a CR2032 or my bench supply. Secondly, and possibly tied to the first, the BATT OK light will not come when powered by a CR2032. The battery tests at 2.98V and works flawlessly in my original uCurrent rev 2 from 2009. Even with 3V from my bench DC supply, the BATT light will not come on.

I inspected the board and it looks like R12 might not have re-flowed properly. This could explain the 1.36V as U1 basically becomes a comparator, but I can't tie R12 as a reason the BATT OK light would fail to come on. Dave, I am completely able/willing to fire up my Hakko with a super fine tip and reflow R12, but I wanted to check to see if you would prefer getting the unit back as-is for inspection or if you want different measures taken. Thanks!

-EM

[EEVblog]

Hmm, not good, sorry about that.
That would have been one tested by the assembly house. So either they missed it somehow, or it is somehow intermittent.
First check from the negative output to either side of the battery, you should measure +/- half the battery voltage.
As for the batt light, there isn't much that can go wrong there, U3 shouldn't be faulty I wouldn't think. There has been the occasional report form the assembler of failed switches, so perhaps that could have something to do with it?
If you email me your snail mail address I can ship another one.

[beaker353]

Dave, I sent you an email to dave@eevblog.com yesterday at 12:19AM US PST. If my math is correct, that would be 5:19PM your time. Hopefully it doesn't get caught in the spam filter...

- EM

[Mosaic]

I have a different problem with mine, it's way off in accuracy, quite useless.

A 3.00 mA load from a battery /resistor/led combo shows up as 2.335mV  on the u current output. A Young Fluke 87V does the current and a 1 yr old 5 1/2 digit Rigol benchtop dmm does the voltage. Measuring voltage drop across the dropping resistor calculates to the 3.00 mA just fine. Battery light says good. Bumping to the mV/uA range shows 1.257V out....which is reasonable as the range is voltage limited.

I am in Trinidad W.I. and just to get a 'free' replacement will prob cost $30 in shipping and duties...

[SeanB]

Resolder the sense resistor, it most likely is dry jointed on the current lead that goes to the switch. Check the soldering on the resistor and the current range switch.

What serial number is yours?  Please post with them, as it makes identification of the units easier.

[Mosaic]

Serial 790.
I did some more tests at higher current; at 24ma it reads 23mV. So its dropping some mV somewhere.

Also at the lower current ranges I am seeing a slightly higher 84uA instead of 80uA. I will do some nA testing later as well.

Can anyone do a 3mA test and let me know if the accuracy is poor in that range or if I definitely have a problem?

[EEVblog]

Serial 790.
I did some more tests at higher current; at 24ma it reads 23mV. So its dropping some mV somewhere.
Also at the lower current ranges I am seeing a slightly higher 84uA instead of 80uA. I will do some nA testing later as well.
Can anyone do a 3mA test and let me know if the accuracy is poor in that range or if I definitely have a problem?

I had someone try to measure 0.5mA on the 1mV/mA range and wondered why the reading was out by a fair amount. That's how these things work, the quoted accuracy only applies at full scale, just like regular meters. 3mA is a bit of a problem because it's just over the range limit, so you have to go to the next range and now your signal is down by 1000 times. So you have to use the 1mV/mA range and you are only getting 3mV output. So the offset voltage becomes a significant part, as does your meter accuracy you are using to measure it.

[burstmode]

Hi,

I received my µCurrend Gold (#00759) yesterday and it shows the same symptoms as described
by the thread opener. As soon as it is turned on:
* Voltage Ouput is fixed to 1/2 Vbatt,
* NegativeOut to vbatt+ = 0,
* NegativeOut to  vbatt- = 1,35.   (1/2 Vbatt)
* The Batt OK LED never lights up.

The soldering seems to be ok, the Switches work correctly.  Any Ideas how to fix that ?

[xquercus]

burstmode,  If your battery voltage is 2.7V as you suggest try a fresh battery.

[burstmode]

OK, mystery solved... ...somehow.

The uCurrent seems to need at least 3.4 Volts to work. At least the one I have here. 
Below 3.2V it stops working (even at 3.15 BattOK goes dark).
I will hook up a few AA Batteries, and live with it.