Modern Electronics (was Re: List charter mods & headcount... ;

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Tue Jun 22 18:24:10 2004

[Microwave ovens]

> Actually, I only have a tenuous grasp (for some suitable
> value of "tenuous") of how the thing works anyway. I've
> only ever possessed one, it currently still seems to

I don't have one of these infernal devices, but anyway...

> cook as well (or badly) as it ever did so I've had no
> cause to examine it in any detail. If it breaks, it will
> get looked at (although I suspect, without ever having
> checked, that a new megnetron will cost a significant
> fraction of the price of a microwave oven). Still,

Most of the time it's the door interlock microswitches (one of them is
_designed_ to short the mains if the others stick closed), the HV
rectifier diode or the HV capacitor that fail.

Be _very_ careful if you work on one of these. They are _lethal_. I've
warned people here about SMPSUs before, but microwave ovens are much
worse. The magnetron runs at a couple of kV and half an amp or so. This
will (not might, will) kill you if you touch it.

Incidentally, the magnetron block is earthed, and is the anode. The
filament (which is a directly heated cathode of course) runs at a high
-ve voltage. The voltage across the filament is only a few volts, but
it's at a couple of kV wrt earth. Just warning you if you decide to try
measuring the filament voltage (in other words, don't do this unless you
really know what you are doing!).

-tony
Received on Tue Jun 22 2004 - 18:24:10 BST