So I got this small circuit that plugs to the mains as power source. as for its DC converter, it's one of those transformer-less ones that drops the voltage with a resistors and filters before rectifying and smoothing it. the ones that can only deliver small currents.
well, after that, it uses two IN4737 zeners in series to create a reference of 15V. I needed to find how much current is being drawn between the 1) DC converter (as described above) and 2) the zeners and the rest of the main larger circuit. so I disconnected the positive wire between these two and put in series an ammeter.
the measurements were odd. using my multimeter, it's here as follows (as I recall it properly):
20A range - 0.06 A
200mA range - 0.006 mA
20mA range - 0.060 mA
2mA range - I can't remember
200uA range - I can't remember
It was a weird set of readings (and yes the number I gave above for each range are exactly as they showed up in my display, even the units). I restored the original connection and the whole thing won't work anymore. I then found out that the IN4737's were blown and shorts at a few milliohms in both direction each.
so what went wrong?? the only difference was the ammeter in series for the positive wire between the converter and main circuit. aren't ammeters specifically designed to be passive and attempt to be a perfect conductor in all cases??