Microwave HV transformer

[davph]

Hi

Can anyone tell me the difference between MD-801FMR-1 / MD-801FTR-1 and MD-801EMR-1 microwave HV transformers?

All I can see is they are all 800W but wondered if they are inter changeable

[CapLeaker]

Probably region codes. AMR for America, EMR for Europe etc. As long as the primary winding has the same voltage than you have in your country, the mounts fit, wattage is the same and the connectors are the same, you should be all right.

[R_J]

seems to be a slight difference in where one of the secondary leads comes out? they should be functionally the same

[CapLeaker]

seems to be a slight difference in where one of the secondary leads comes out? they should be functionally the same

That may explain the last picture, but not the first two.

[R_J]

.

[Agent24]

Looks like the differences mainly lie in the connector arrangement, for different design styles of oven, I would guess.

Also one (MD-801EMR-1 by process of elimination) seems to have an electrical connection to the core, while the others don't appear to?

[R_J]

The high voltage winding has one end connected to the core (ground) they all have that., the other end of the high voltage winding is either a wire lead with spade connector or just a spade connector on the transformer. The other leads are for the filament and are only a couple turns around the core to provide around 3 volts
The FTR and EMR seem to be more similar, maybe lead length is different?

Is the one you have defective?

[davph]

I think the one I have is defective. HV fuse blows instantly when start button is pressed.
Door switches, diode and capacitor are ok and have swapped the magnetron as I had a good replacement.

There is a tap on FMR that the HV fuse connects to. From what I can see the FTR doesn't have this lead connects straight to capacitor.

I've never had a faulty micro transformer.

[R_J]

You say there is a fuse in the high voltage secondary lead that blows? if this is the case, it is not the transformer and more likely the diode or cap.
Usually, the problem is the door switch is bad (stuck closed) and the monitor switch closes blowing the main fuse.
I supplied a diagram, your transformer connections to the magnetron, cap, diode should be similar
I have had shorted components (cap, diode etc.) on the secondary and they would load the transformer causing it to hum very loud but not blow the fuse instantly.
it is rare for the transformer to go bad, and it is usually the high voltage secondary that shorts or arcs.
Post the make and model number or maybe a couple pictures

[davph]

Model is Bosch HMT75M451B/35

I re checked switches which are ok and no shorts on cap or diode. Decided to swap capacitor and diode and Its now working!!

I only had 0.95uF instead of 1uF

[R_J]

It is likely the diode that is bad, you can't really check them, they are a stacked diode, the cap value is not critical. Good to hear it is working
It is possible the cap is shorting under load, but the diode is more likely.

[sam_sam_sam]

Model is Bosch HMT75M451B/35

I re checked switches which are ok and no shorts on cap or diode. Decided to swap capacitor and diode and Its now working!!

I only had 0.95uF instead of 1uF

The high voltage diode is very hard to test with a multi meter and the capacitor might be damaged so when I see the main fuse blows I change both the diode and capacitor which works most of the time unless you have a bad magnetron that is partially shorted which is causing the fuse to blow