SDG #067 Don't blow up your oscilloscope! Micsig Differential Probe for $140! (See link)

Probing mains referenced or floating circuits with a standard passive probe is one of the fastest ways to destroy an oscilloscope, blow a fuse, or receive a serious shock, because the probe ground clip ties the measurement point directly to earth through the oscilloscope chassis. This review examines the Micsig differential probe as the sensible answer to that problem, and explains why a differential front end is a better solution than the common workshop expedients of floating the oscilloscope with a defeated earth or using an isolation transformer.

The practical points a buyer cares about are covered: the high common mode voltage rating that allows both inputs to sit well above earth potential, the switchable attenuation ratios and how they trade resolution on small signals against headroom on high voltage rails, and the bandwidth on offer relative to the price. Common mode rejection is the specification that really matters, since a differential probe is only as good as its ability to ignore the large voltage both leads share while faithfully reproducing the small difference between them. Build quality, the lead set, and the power arrangement for the active electronics are also considered.

The verdict is aimed at hobbyists and repair technicians working on switch mode power supplies, motor drives, inverters and half bridge topologies, where high side gate drive and unreferenced nodes are routine. At this price a probe like this is far cheaper than replacing a damaged oscilloscope front end, and it makes measurements possible that cannot be done safely any other way. Anyone working on live SMPS boards should treat it as essential equipment rather than a luxury accessory.