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GE microwave blows line fuse within seconds of starting

When unit is started-it will hum loud then blows fuse, I removed the primary leads to trans and the light,turntable fan and display work fine. I have tested the trans, magnetron, cap and hv diode more than once and they all appear fine I even checked the hv diode with a9 volt battery in series. If I plug the primaries back in and start it -it still will but the Trans hums loudly but did not blow the fuse, ( I only ran it for 5 sec each time) So am I guessing that it is the trans since its secondary leads are not plugged in ? Thanks.

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Process of elimination- primary only on transformer and hummed very loud , tried a different trans and once again only plugged in the primary's and it purred so I wired up the cap, hv diode and megatron and it works purr-fect ! Only thing that bothers me is that the loud transformer when tested multiple times showed primary , secondary windings and hv tap all showed good - so I'm stumped why it was loud but tested ok ?

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It’s likely that when high-voltage developed (high amperage) it was shorting to ground somewhere. Kind of like a high volume of water through a hose. The loud noise is usually caused by the original short to ground back feeding the HV diode to the capacitor in which case the HV diode is bad because it is now allowing voltage to ground.

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