Just an anecdote, a coworker was tasked to verify ESD compliance of work surfaces using a handheld ESD meter; he did a meter zero, walked a few steps to the work surface and found the surface to be noncompliant, at around 90V potential, solely from the static charge from walking the few steps. He had to ground himself to the local ground after the meter zeroing to kill the charge being built up from walking a few steps.
While modern chips are plausibly robust (some boards can handle kilovolt zaps on their external I/O pins, others are not, and you don't know which ones are which until they die, or you've tested them, in the wild.
Grounding yourself to an oscilloscope ground helps to spread the charge, since the oscilloscope, when unplugged, is essentially a large capacitor, like your body. However, there may be residual charges floating around on things that weren't adequately grounded prior to unplugging. I've personally gotten zapped by a piece of equipment whose grounding bar didn't make adequate contact prior to my touching the equipment. I wound up flat on my back from the zap.
My suggestion:
> turn off equipment, but don't unplug yet
> ground yourself to the equipment first
> wait 20 seconds
> unplug equipment
This allows time for you to equalize the equipment and allows time for any high voltages or charge to dissipate
beyond before you touch anything inside.
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
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