Matt Mc_Carthy wrote in a message to JIM HOLSONBACK:

 MMC> The old ones generally have a BIG XFmr, a BIG capacitor with a 
 MMC> bleed resistor across it, the magnetron, and a HV diode.  I don't
 MMC> think the XFmr in those would ever die, wiring is monstrous!  [New
 MMC> machines use switching PSs, no XFmr]. 

Those are *dangerous*,  too.  Put out _amps_ at kilovolts!

 MMC> Never saw a capacitor go either.

Nice to know.

 MMC> One of my old Littons had a dead diode, the other cooked a 
 MMC> magnetron.  The diode [in 1974] cost me $17, was a simple repair, 
 MMC> the magnetron in the other cost me $400 [in 1975], and a LOT of 
 MMC> conversation with the parts place, as I wasn't a "licensed 
 MMC> repairman" and he didn't want to sell to me.  Times have changed
 MMC> though!

 MMC> When the magnetron goes, it is most often a cathode short, the 
 MMC> unit sucks power like mad and dims the lights on older houses
 MMC> before blowing a fuse.

 MMC> Random showers of sparks flying around indicates an open diode,
 MMC> therefore no DC and no oscillation.

We had _one_ die on us,  and it just simply wouldn't heat any more.  I
suspect a diode,  but never got around to doing anything with it.  My
brother has it now,  and will maybe get around to fixing it at some point.

 MMC> As noted in Roy's reply, the diode is not 'testable' without a few
 MMC> tricks. The easiest way is to simply connect a 9V battery in 
 MMC> series with one of the meter test leads on an old analog 
 MMC> multimeter set to it's highest Ohms scale.  The 9V is enough to
 MMC> overcome the reverse breakdown rating and get a reading.  BE SURE
 MMC> to NOT try zeroing the meter while the 9V is connected!  Do that
 MMC> first!   :-))

Ah.  Nice trick,  I wish I'd known that then...

 MMC> Goes without saying, don't trust that bleeder resistor to be
 MMC> functional, check or discharge the capacitor first.  It can hold
 MMC> 2400V to 10KV, and seems to have more 'punch' than a TV HV.

Oh yeah!

 MMC> You NEED an HV probe to get anywhere near the HV section, but I 
 MMC> don't see any need to be concerned about what the HV is.  It 
 MMC> works, or it doesn't.

Just so.

 MMC> If you need a magnetron, "mat electronics" [believe they are in
 MMC> PA], had a catalog of replacements for older units, ran from $24
 MMC> to $95.  Might be able to dig up an old catalog and see if they
 MMC> have any web address.

They're out there...

 MMC> New units being so darned cheap and 'disposable', it hardly seems
 MMC> worth the effort, but it is still fun testing and trying to find
 MMC> the problem. 

That's the kicker.

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