Author Topic: CR shows "OVERLOADED' when scope probe attached  (Read 154 times)

rberk

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CR shows "OVERLOADED' when scope probe attached
« on: February 23, 2020, 10:15:20 PM »
I received my CR mk3 a week or so ago and have been doing some great work with it. Boy, what a great tool!
Unfortunately, today I did something really stupid. I put reverse polarity on my DUT for about 5-10s until I figured out something was not right. During this time the CR showed around 1050mA current draw (from a 4V supply). While this was going on I had my scope probe inserted and the scope turned on. My DUT is fine (phew!), my Current Ranger seems to be working fine with the oled plugged in, but as soon as I attach the ground lead of the scope probe, the CR shows "Overloaded" with ~3250mA (I forget the exact value) showing on the oled display.
Eek - what have I done?
I opened up the CR and there are no obvious signs of damage, but there does seem to be a small area on the board where the components seem to be slightly moist, as if something has leaked? See photo. When I attach my DMM and try and read the output, everything seems to read fine! I just can't do the same with the scope. Have I damaged the scope? If so, how? I can still see and capture a trace on the scope but I don't seem to be able to get measurements anymore. That said, I'm fairly new to the scope.
Any insights greatly appreciated.

Felix

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Re: CR shows "OVERLOADED' when scope probe attached
« Reply #1 on: February 24, 2020, 10:47:50 AM »
I put reverse polarity on my DUT for about 5-10s until I figured out something was not right. During this time the CR showed around 1050mA current draw (from a 4V supply)
I see it appears there's an actual liquid on the board, but that can't be from any electronics, the only thing they might ever leak is blue smoke  ;)
Are you sure you didn't drop some water or some liquid on it?
The battery (LiPo?) would also not leak, especially up against gravity.
The other possibility is if the components got really hot and condensed humidity, but that much?

Anyway my main question is - what exactly was the 4V supply?

rberk

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Re: CR shows "OVERLOADED' when scope probe attached
« Reply #2 on: February 24, 2020, 11:30:19 PM »
Thanks for responding Felix! Well, another day, and I'm happy to report that everything is behaving itself again. I booted up the scope this morning and I can get believable measurements again (yay!) and no more "overloaded" error messages on the CR. Not sure what happened other than perhaps my scope got out of whack with the incident and needed re-booting?? To answer your question, it was at 18650 lithium ion battery I was using as my supply.
As for the moisture, that is still a bit of a mystery. I soaked it all up with a cotton bud and it seems ok this morning. All I can think is it may have been some condensation? We have had some exceptionally hot and humid days followed by a relatively cool day yesterday? I'll have to keep an eye on that as that is potentially another smoking moment! Thanks again for a brilliant product and wonderful after sales service! I just hope I can avoid another d.i.y disaster!

Felix

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Re: CR shows "OVERLOADED' when scope probe attached
« Reply #3 on: February 25, 2020, 09:28:14 AM »
Thanks for the update and the feedback.
As long as you heed the warnings in the safe use guide you should be good. This is because CR is a high side current meter and it is rather easy to force current loops through the device if external connections from earth grounded supplies/scopes are made. I have tried to add more isolation through passives but still full isolation is required outside the device (or floating supplies to be used as recommended) to ensure it will not be damaged by current/ground loops.