OK τώρα το είδα. Η δίοδος φαίνεται ΟΚ. Η αντίσταση που μετράς από τον ακροδέκτη της μάγνετρον στο σασσί όντως προβληματίζει..Παραθέτω το επόμενο κομμάτι από troubleshooting material για φούρνους με μικροκύματα. Έχω κάνει bold και έχω υπογραμμίσει το κομμάτι για τη μάγνετρον που συζητάμε..
There is no totally definitive way to determine if a magnetron is good without
actually powering it under operating conditions but the following tests will
catch most problems:

* Magnetron filament. The resistance should be infinite from the filament
connections to the case and a fraction of an ohm between the filament
terminals with the wiring disconnected from the magnetron.

While measuring resistance from filament chassis, gently tap the magnetron
to determine if there is an intermittent short. However, such problems may
only show up once the filament heats up and parts expand.

It may be possible to determine if the magnetron filament is actually
working by connecting just the filament connections to a low voltage
high current supply on a Variac (e.g., a microwave oven transformer but just
the filament connections). The ceramic insulators are translucent and should
show a glow with a working filament. The one at the antenna may be visible
if the magnetron is removed from the oven or with a dental mirror looking
into the waveguide. WARNING: Make sure you ONLY have the filament connected!

* Evidence of arcing (visible blackening around ventilation holes in base or
burnt odor) usually indicates a bad magnetron.

* Melting or other damage to the antenna cover ('bull-nose' or 'bullet') may
be the result of arcing due to problems in the oven cavity or waveguide
(perhaps operating with nothing in the oven) or a defective magnetron.

(This part is only visible with the magnetron removed from the oven). If
a problem elsewhere has been corrected, the damaged antenna cover can be
pulled off and replaced from a magnetron that died of other causes - try
your local appliance repair shop. (The shape doesn't matter as long as
it fits tightly - there are several diameters, however.) Your magnetron
may still be good.