WARNING: MICROWAVE OVENS CAN BE LETHAL!
A microwave oven is a very dangerous device. Even service personnel who are very familiar with them will tell you they are not their favourite equipment to work on. A microwave oven operates at a potential of several thousand volts and contact with any part of the high voltage circuitry can be (and indeed has been) fatal. Even a microwave oven which has been turned off for some time may have enough energy stored to give a potentially lethal shock.
NEVER operate a microwave oven without the cover on and secured and without the door interlocks operating.
This article is intended for those who are experienced with mains device wiring in general and microwave ovens in particular. Follow exactly the steps outlined in this article regarding making the microwave oven safe before, and as you modify it.
Why not, indeed? I
wouldn’t have the lid of the original design to clamp the transparency down onto
the PC board but this could be overcome by making a platter and using a sheet of
glass to apply enough weight to ensure intimate contact.
When activated, the platter-motor of the oven, slowly rotates
the PC board pattern within the UV light, providing a very even exposure of your
pattern. I can obtain very even and consistent results with transparency film
and about 30-40 seconds exposure time (although I tend to pre-heat the tubes for
five minutes first). There is a significant difference in both light output and
colour temperature between a just-turned-on tube and one which has been on for a
One big advantage of using an old microwave oven: just as when
the oven was an oven, when the time is up, the oven beeps loudly at you, to tell
you that your board has finished cooking exposing!
So I bought a secondhand microwave oven for $5 from my local
refuse recycle centre, in a "working but no glass turntable" state. If your
council has kerbside cleanups, you may well find one that’s about $5
By far the majority of microwave ovens are discarded because a
30c high-voltage diode has blown. But we don’t even need that because we aren’t
interested in the cooking side of things.
The only things you need to check, when looking for an oven to
convert, is that (a) the timer and its display works and (b) that the platter
motor turns. It does not matter if the oven has a glass platter or not – I made
my own from a sheet of MDF and an old speaker.