Mike Harmon

I'm working on an old Motorola power supply. One of the adjustment steps says to connect a scope between the positive DC output terminal and a +41V test point inside the power supply, and look at the waveform. I have a 7904A with 7A26 vertical plugins. The problem is that whichever point I connect the common probe lead to is going to be taken to chassis (earth) ground! I'm not comfortable with lifting the scope chassis above ground by disconnecting the ground wire at the AC input.

I think I have an old A6902 Isolator unit somewhere in the dungeon that someone stole the probes from. As I recall, the only thing in the side bage is the pigtails coming out of the isolator to connect the probes to. Would it make sense to just connect a standard scope probe to the pigtail(s) and feed the isolator to the scope's vertical input?. I guess I'd have to install a BNC female connector on the end of the pigtails. Getting the correct probes for the isolator would cost more than the isolator is worth. I've had it for years and this is the first time I've thought of trying to use it!

Is this a crazy idea? Does anyone have a better (safer) way to measure the differential waveform?

Thanks for the help!!
Mike Harmon, WB0LDJ
mharmon at att dot net

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