Charging CurrentRanger through USB from PC while having DUT ground connected

[frohike2008]

I have been using CurrentRanger for years without any issue, but unfortunately, I forgot to not charge the battery from PC USB and the same time powering DUT with a device with mains connection.

Now if I start CurrentRanger the green Led is ON for 2 seconds and it goes off. There is no led on in the ranges buttons, neither any image in OLED display. I saw a similar question in this forum
"connected USB to CR while having DUT ground connected with the laptop ground" and you told that replacing MCU it should be enough to repair Current Ranger.

Is this true? only MCU is damaged in this situation? I don't see anything strange looking at the PCB (no burn traces). If you can confirm me this, I can replace the MCU instead of buying again another CurrentRanger.

[Felix]

Hard to guess what really happened.
I'd have to diagnose. But yes most likely you zapped the MCU pretty good and now it acts funny, and a replacement could solve the problem.

[frohike2008]

What keeps VIN after pushing ON button? The MCU or the MCU only powers Off VIN?

I can see VCC doesn't reach 3.3V when pushing the button, it only goes to 1V or something like that. Maybe MCP1703 LDO is broken and doesn't output enough voltage for MCU?

[Felix]

That's possible, a bad LDO can collapse the VIN/VCC rails.
The power circuit is independent of the MCU. The MCU can trigger it to cut power off.