Convection Microwave Sorta Dead

I've got an old convection microwave that's probably seen it's better days, but I thought I'd throw this out here and see if there are any ideas. It's actually on it's second magnetron tube, which I replaced like 8 years ago. The symptoms (way back 8 years ago) were when you tried to nuke something, it made a loud hum (loud enough to say "oh sh*t" and turn it off).
This time, the controls seem to work fine (set it to nuke or to "convect" something, the timer counts down as long as the door is shut... just exactly like it's working), but the fan motor doesn't start, there's no gentle hum of nuking. Set to convection, the fan motor doesn't start (I didn't leave it on long enough to see if the heating element heated).
Anyway, it sounds like maybe the momma transformer has given up the ghost. Yes? The baby transformer is putting out it's 13, 3, and 8, like it should, which is why the control panel is so happy.
It's a 1993 GE, so, yeah, I got my money's worth out of it, but new ones are like $600 (over the range version), and it ticks me off that you can get one just like it, but without convection for $200.
So do folks here have a theory? Something for me to try?
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Anybody? The ohmmeter over the internal 15A fuse shows continuity.
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sengsational wrote:

www.repairfaq.org has lots o' information about microwave ovens.
Is there some kind of interlock that prevents the magnetron from nuking if its cooling fan doesn't spin? I think I saw a sail switch for this in ours.
www.microwavedisplays.com has lots of oven repair manuals available online at no charge.
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wrote:

Thanks for the reply. That site is going to take some serious time to pick through!

Yeah, the interlocks seem to be working, but I'll double check. There are two on the door. Opening the door stops the count-down clock, so at least one of them is working. I tested both, and they both change from open to closed (or closed to open) when the door is open and shut. Might there be some other interlock besides the door? I have the schematic, so I'll have another look.

The site that used to be there must have moved....there's just one of those "junk" sites there now...parked on that site, trying to sell it for $500.
--Dale--
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