Damaged CR

[PatrickC]

I think I damaged the CR by plugging the USB to a Raspberry Pi 4 without an isolator.  I forgot about the isolator because I have been able to use my other CR with my PC laptop for a year now (and it's still working great).  I wanted to do the data logging on the RPi 4 I have available instead of my laptop.  Unfortunately, the moment I plugged the USB into the RPi,  the CR's screen was flickering, and it was rebooting every few seconds until I unplugged the cable.  At this point, I think it's damaged.  It can no longer measure any current going from PSU to DUT terminals.

The USB functionality seems OK when I plug it into my laptop (with an isolator this time).  I can connect to it via Putty and bring up the commands with ? and then do various settings.  Unfortunately, there's no current reading at this point.  I can turn the bias mode on, and it'll read something, but I don't think it's a correct reading.

We just bought this CR less than a few weeks ago.  It won't be easy to ship back due to all the hassle of purchasing and shipping here.  I can repair the CR myself if I know what components to replace.  I wonder whether it's worthwhile for the next version of the CR to include a USB isolator circuit already.  It would add maybe $20-$30 to the overall cost, but that's much less worrisome for the user.

[Felix]

It's hard to estimate where the damage is because a ground loop can do all kinds of damage.
Usually it's the MCU in this case but it can be other things.
In any case a repair is not very straight forward and debugging it can be time consuming.
I have tried this kind of repair in the past with varying amounts of success.
I understand it's easy to forget but there are warnings placed as a reminder even on the front of the PCB right next to the USB.
I have discussed this previously about including an isolator and the conclusion was that it would make the board too expensive and bulky to make and a lot of people would not benefit from it given how they use the CR.

[patratacus]

Miraculously, it seems to be working again after I was doing some probing of the MOSFETs trying to see if any of them were damaged.  I didn't find anything obvious, but whatever I did seemed to have brought the CR back.   I checked it with a 470ohm resistor and 5V input and was getting around 10 mA, which is correct.  I compared it against a Keithley 2420, and the values are nearly identical.  I tried measuring an MCU that I did some benchmarking before, and the result came out the same.   

I'm pretty happy that it's working again.   I also made sure to attach the USB isolator with the CR so it won't be accidentally plugged into a computer without one.  I was able to plot the data using the CurrentView, and everything seems to be working correctly on the Raspberry Pi 4.

[Felix]

That's good to hear, thanks for the update!