On 14/05/2021 16:13, Chris Bacon wrote:
On 14/05/2021 15:40, Peter Able wrote:
On 14/05/2021 13:31, Chris Bacon wrote:
High voltage transformer: Primary, isolated, about 2.2 ohms.
Secondary 150. There is another winding that seems to go to the
magnetron, I don't know what this is.


Magnetron filament winding, connected to the two magnetron terminals.
Disconnect at the magnetron and check that this transformer winding
and the magnetron filament are OK (fraction of an ohm - but not zero).
One side of the filament circuit will be connected to the diode's
anode. The other magnetron connection (its anode) is via the
magnetron's body.Â* The transformer HV secondary should have one end
connected to the transformer body, the current path between this and
the magnetron anode being via the chassis.

Thank you. OK, I disconnected at the magnetron, and there seems to be a
tiny resistance through the few red/black flecked fabric-covered coils I
can see in the middle of the transformer. Maybe 0.1 ohm, but my meter
isn't particularly precise.

Is there anything else to measure?


A blown filament shouldn't blow a fuse, though.Â* Slightly worrying
that the fuse has blown before !

It's quite an old machine now, and I have heard that the fuses can go
after repeated uses.... coincidentally, I had just used "low power"
Â*to simmer things; this seems to be full power but switched on and off
every so often....

OK. Do you mean that you've replaced the fuse and can use the lower
power mode for ever - but when you try full power it fails and blows the
fuse? If so, how long does it run full power before it fails.

Has the microwave been stored in a garage? That can result in
transformer damage when powered up?

PA