24 replies to this topic

[ibis81]

So i did the test outlined. I ran the microwave with the magnitron disconnected. Everything seemed to run fine.

After I did the test. I unplugged everything. When I shorted the capacitor it did not appear to have held a charge, nothing at all. Is there anything that could account for that?

I am thinking that the high resistance reading I got on the transformer (1.2ohms instead of .25ohms) indicates a winding fault int he transformer. That would mean that the capacitor is not being charged correctly by the transformer. When I test the capacitor it responds correctly as noted above. Also the diode seems to function properly so its not draining the capacitor.

Am I on the right track, or way off base?

[RegUS_PatOff]

I wouldn't think the Transformer would increase in resistance..
It would normally "open" or "short"
Are you using a digital OHM meter.. ?
on the 200 OHM scale ?
and when it's probes are shorted together.. reads 0.0 ?

[ibis81]

I wouldn't think the Transformer would increase in resistance..
It would normally "open" or "short"
Are you using a digital OHM meter.. ?
on the 200 OHM scale ?
and when it's probes are shorted together.. reads 0.0 ?

I am using a digital multimeter that zeros when the probes are touched. High voltage tap to chassis reads 63 which is correct. From primary to primary it reads 1.2 (spec is .25). Filament to filament is 1.2 (not sure what spec should be). filaments to ground is infinite. primary to ground is infinite. I read elsewhere that a substantially higher primary to primary reading could indicate an open winding. I dont know if 1 ohm is substantial in this case or if an open winding would cause the capacitor to not charge.

Any help is greatly appreciated.

[ibis81]

I am using a digital multimeter that zeros when the probes are touched. High voltage tap to chassis reads 63 which is correct. From primary to primary it reads 1.2 (spec is .25). Filament to filament is 1.2 (not sure what spec should be). filaments to ground is infinite. primary to ground is infinite. I read elsewhere that a substantially higher primary to primary reading could indicate an open winding. I dont know if 1 ohm is substantial in this case or if an open winding would cause the capacitor to not charge.

Any help is greatly appreciated.

So it looks like the capacitor has an internal discharge resistor. So that's why i get no charge. Maybe I am over thinking this and the fuse holder melted because of a poor connection. The only thing that tests out of line is the HV transformer as described above.

[RegUS_PatOff]

... primary to primary it reads 1.2 (spec is .25).
... Filament to filament is 1.2 (not sure what spec should be).

yes.Transformer Primary winding should be 0.25 OHMs
Transformer Filament winding should be 0.4 OHMs
(as shown in the service manual)
IF the Primary was "open", I wouldn't think it would blow the Fuse.