Hi
Is there any problem with investigating the internal of a microwave oven ? Not turning it on of course.
Mine has developed an intermittent rattle, which stops if you press on the case side and I suspect it is just something slightly loose but I have no means of testing it, once the case is replaced or should I just bin it ?
Andy
I believe they have a huge capacitor or two inside them. Also you can get quite a good belt off the turntable motor if you spin it manually whilst touching the contacts. DAMHIK, IJK.
Si
Shouldn't be - they only radiate when powered up. As with any electrical equipment be wary of the capacitors which may still hold charge, even long after the equipment has been powered down. The capacitors in microwaves are particular high capacity. In my microwave, there is a huge red warning sticker attached to the capacitors to make this clear, but yours may not have this. If you have any doubts about what a component is, don't touch it!
dan.
There's a fatal charge waiting on the capacitors inside it. There _ought_ to be discharge resistors across them, but you never trust those things. Don't open the case for an hour or two after power, then make sure to discharge the capacitors with an insulated probe, in case the resistors were what had fallen off! This probe needs insulation to HT standards, so a clean, dry rod handle of glass or non-conductive (i.e. transparent, so you can see there's no carbon filler in it) plastic is needed. Aldi are selling packs of cheap knitting needles in bright transparent colours at present, which make excellent support insulators if you're making steampunk Wimshurst machines.
Personally I'd leave it a day first.
Web searching the Tesla Coil and Jacob's Ladder building sites will suggest much about what to do with the innards of a microwave.
SIDE!
Andy Cap used his keyboard to write :
The capacitors inside can store a couple of thousand volts for quite a long time. They are supposed to be fitted with a high value resistor to discharge them, but that can go faulty. Best to make sure these are discharged before probing about inside.
Thanks to everyone who's warned of the dangers. I will take a careful look over the next few days.
Andy
I had one that was making noises and overheating.. took the back off and a big warning label had detached itself from somewhere inside and had jammed the fan. It worked after removing it but was never quite as powerful as before so something was damaged. Chucked it and bought a new one for ~£40.
Many moons ago... I had a brilliant Panasonic combination oven I couldn't stand the thought of dumping as it cost me around £500 when I bought my first house... Microwave had packed up and general opinion was the big capacitor was shot. Got a new one mailorder, fitted and lo & behold the beauty was revived.
As others have said, a big cap. can give one hell of a belt if it's not discharged. Been there, done that.
8¬OPete
In message , snipped-for-privacy@googlemail.com writes
Bad, bad, bad. If you have no idea of the safety implications of opening a microwave, don't do it. It is highly likely to kill you if you touch the wrong bit inside and it can kill you weeks after you unplug it given certain fault conditions (that wouldn't necessarily affect normal operation). I believe the newer inverter ones are safer but even so...
Unless it's something really special, leave well alone or buy another one and if it is something really special then get someone who knows how to service it safely to do it.
Putting newspaper between it and whatever its next to might be easier.
That capacitor is the biggest safety deal in nukes. Advice to leave it
24hrs does not inspire confidence, if the discharge resistor is o/c chances are it can still kill you after a week. Avoiding the cap doesnt work, the wires will conduct the lethal charge around the place. Only safe option is to discharge it before getting in there. Attach a wire from cooker case to screwdriver shaft, and use the blade to touch _both_ cap terminals _together_. Screwdriver must be insulated and hands kept away from bare shaft. People have died servicing nukes.NT
If the capacitor is that big, you'd better put safety goggles on before shorting it with a screwdriver. Better to use a resistance. My boss who should have known better, tested a large capacitor with a 5kv tester. I wondered why it took several seconds to reach the 5kv. When he shorted it with a screwdriver it blew the end off the steel screwdriver and bits of flying molten solder went everywhere.
Switch Off Isolate Dump Earth
I remember seeing a short documentary about that with two guys in a lab. One goes off to the dentist and the other has the task of rewiring the experiment. Imagine his surprise when he touches a screwdriver somewhere unexpected and there is a flash and a loud report
Give that man a cee-gar.
Wasn't it one of those day-time fill-in programs that existed before Jeremy Kyle?
Most microwave capacitors have built in 15Meg resistor and discharge pretty quickly, in minutes...
Today's "news" story about defibrillators and swimming pools (together with this thread) inspires the thought that the kitchen microwave could form part of the core equipment for the d-i-y "Home Hospital and Operating Theater" (TM).
Waveguide out and you've got radio-frequency diathermy machine as well.
Brain surgery with Bosch cordless drills already covered.
that currently only serves as a squirrel, free meal station?
S
Phew.
Wish I could have read this when I had to change the table motor on our Bosch. I was pretty careful because of the radiation situation and not wanting to render the equipment dangerous in that way, but I hadn't appreciated how long the capacitors may have remained charged! (Though there are high voltage warning signs around them so care was indicated.)
One interesting feature of the oven, - which came apart satisfyingly easily - was the half punched out plate in the casing below the motor. Indicating it had been expected to fail, so they had thoughtfully provided the knock out to speed up the replacement! Why they could not have simply left a hole and saved a bit on the metal is something of a mystery. The blanked out bit makes an interesting tea cup coaster though.
Incidentally, the fan and it's guard are quite tricky to get into a position that does not rattle now and again. I can live with that.
S
I'm not sure who Jeremy Kyle is.
However, I did remember where I saw this film first. It dates back to the 1960s and was used for BBC2 monochrome test transmissions prior to its launch in 1964.
About ten years later, I worked with a guy (sadly no longer with us) who had not long earlier co-invented some of the very first digital TV standards conversion equipment when he was at the IBA (as was). They used this film, plus another one which was a travelogue about Tunbridge Wells and had several long panning shots across tiled roofs. The flashes in the SIDE one were very good for testing recovery of the picture after a sudden massive overexposure on the film, while the tiles tested how well the conversion equipment could keep up with massive detail movement. In the end, the return didn't come so much from that functionality because sales volumes were not that high, but when the technology was used in broadcast video effects equipment.
Its only a couple of uF, but its enough to kill several people.
NT
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