I've got a TL866II universal programmer that has a fault on ground pin 20. I do not know what the fault is, but I'm thinking about doing some probing with the scope to see what happens during the failing self test of the device. In order to start a self test, it needs to be connected to a computer via USB.
There is a risk of me probing something wrong, or shorting something. So I'd like to setup the test as safely as possible. I want to try to avoid destroying the device under test, the oscilloscope, the computer, and (definitely) me.
I've read tips about using a powered USB hub in order to protect the computer. Currently looking at maybe buying a TP-Link UH720. It boasts:
a sophisticated circuit design with multiple protections for your devices against over-heating, over-current, over-voltage and short circuit.
Sounds pretty good. Yet, it says in the manual that it works even without external power. Actually all the powered USB 3 hubs I found says that. It makes me wonder how protected the power lines between the hub and the computer really is?
Are there any other measures I should take?
I've read about USB isolators. Some say to always use them, other say they are dangerous.
I've read about differential probes, but it's not completely clear to me if there will be any advantage since it's low voltage (on the DUT, at least).
I've read about probing when connecting the USB device to a laptop on batteries. I feel there is conflicting advice about this as well.
Appreciate any advice.