You can always check the probe with a DC current and check the latter with a multimeter. @Bidule0hm your series resistor wasn't coiled up tightly so it doubled its resistance due to getting red hot, was it?No, the scope doesn't have a 50-ohm termination option, but the probe calls for a minimum 10k impedance anyway. I'll see if I can find anything else.
your series resistor wasn't coiled up tightly so it doubled its resistance due to getting red hot, was it?
The probe was zero'd by adjusting the vertical position of the trace to be at the desired place on the screen--the scope is measuring peak-to-peak, so the exact level shouldn't be that important. I just checked its calibration by placing a 20-ohm resistor across a (nominal) 12-volt battery, in series with my Fluke 87V measuring amps. The Fluke and my scope were within ~10 mA. Not quite the 1.5% accuracy claimed for this thing, but still reasonable.
Most drives do not use the 3.3V rail, to maintain compatibility with molex connectors, which only supply 12V and 5V.There's also a +3.3V line, but there doesn't seem to be any current flowing on it.