Microwave Repair And Safety Question - Page 1
Forum section: electronics / repair

author: EvilGeniusSkis
author_rank: Regular Contributor
timestamp: June 12, 2017, 03:13:56 pm
content: Is it safe to run a microwave with the shell off like thisfor testing purposes?[I know to be super careful about the high voltage and the microwave radation] My microwave failed in a weird way, on 100% it would run for ~30s, then shut off, on 50% power it would run but not properly. It got a plastic splatter coverall hot and floppy, but didn't heat the food underneath at all. The only thing resembling skid marks I've found it the sticker on top. Needles to say I'm puzzled as to why it failed.EDIT:I've written it off, I tested it completely assembled and heard arcing,NO WAYam I messing with 1000W @ several kV

author: oldway
author_rank: Super Contributor
timestamp: June 12, 2017, 06:45:44 pm
content: In the repair café, we have a safety procedure to never let the high voltage circuit to be energized with the shell off...At least, it has to be in place, not necessarly to be tightend ....Safety concern is principaly with high voltage (2 or 3KV) and high current (0.7 to 0.9A) which are lethals.

author: Bushougoma
author_rank: Regular Contributor
timestamp: June 12, 2017, 07:19:32 pm
content: Ugh it looks like an inverter microwave do yourself a favor and stay away from them way too failure prone. Get one with an old fashioned 60 hz transformer if you can find one. Just the manufacturers way to reduce the copper used in the step up transformer (because it's switched at a higher frequency) at the cost of complexity and reliability.Arcing? Sounds like the magnetron is shot just replaced mine earlier this year it took out the rectifier too with the cover off I could see the blue light through the vent holes while it was running it was arcing somewhere inside.No they don't always fail totally short circuit between anode to case or heater to case and can't always be tested with the resistance range of a multimeter sometimes live testing with the cover off is necessary. The transformer also buzzes like an angry hornet when there's a short circuit on the secondary.Unless it's an expensive over range model like mine was it's probably not worth the cost to repair.The RF energy comes out of the magnetron antenna and goes straight into the wave guide the magnetron has a mesh gasket around the antenna to prevent leakage between it and the wave guide so yes you can operate it with the outer housing off. The wave guide then ends inside the cooking cavity it's under that shiny (mica?) sheet that RF can penetrate some pricier models have a metal stirrer blade driven by a motor just above the sheet to more evenly cook the food.The only real danger with it unplugged comes from the high voltage capacitor which usually has a high value bleeder resistor across it that will discharge it over time. But it's always a good idea to make sure it's discharged by shorting it with an insulated screwdriver in the event the bleeder resistor has failed. This applies to microwaves with a linear transformer.

author: uski
author_rank: Frequent Contributor
timestamp: June 12, 2017, 08:52:10 pm
content: DO NOT disassemble the magnetron and if you do, be very careful to NOT damage the ceramic isolators inside.They are made of barium oxide and a SINGLE contact with the dust can create life-lasting health problemsSkin contact is a problem, let alone breathing the dust.Be very careful !

author: EvilGeniusSkis
author_rank: Regular Contributor
timestamp: June 12, 2017, 08:59:56 pm
content: Like I said in the edit, microwave is written off. I wasn't unsure about the high voltage safety [ that's easy, don't touch it], so much as whether the outer shell was an important shielding component. My main reason for wanting to run it with the cover off was to use an IR thermometer to see what was getting hot.

author: xavier60
author_rank: Super Contributor
timestamp: June 13, 2017, 08:32:42 am
content: It is interesting to know that when a microwave oven magnetron appears to be short circuited, usually it is the RF bypass capacitors in the power input socket that are causing the short.

author: amyk
author_rank: Super Contributor
timestamp: June 13, 2017, 11:38:23 am
content: Quote from: uski on June 12, 2017, 08:52:10 pmI'm pretty sure consumer microwave magnetrons don't contain barium.If you meant beryllium, I don't think so either --- otherwise they would have very prominent warning labels and cost far more.

author: Psi
author_rank: Super Contributor
timestamp: June 13, 2017, 11:48:47 am
content: i'm pretty sure at least some consumer microwave magnetrons contain beryllium, if not most

author: chris_leyson
author_rank: Super Contributor
timestamp: June 13, 2017, 11:56:09 am
content: Come on guys you're not thinking things through. The ceramic insulating discs between the electrodes are not Beryllium oxide. You wouldn't mount a BeO cooler on something with a forced air cooled anode would you now.

author: bktemp
author_rank: Super Contributor
timestamp: June 13, 2017, 01:03:54 pm
content: I hear the stories about beryllium in magnetrons all the time, but I can not find any reference for that. Wikipedia says some magnetrons may contain beryllium, but does not give any reference. Service manuals also do not contain any warning. Therefore I think is is rather unlikely:- If there is something dangerous in a consumer product there would be a warning label on the back. There is a high voltage warning, but no warning about toxic chemicals.- A microwave is used for heating food and a fan is blowing air across the magnetron into the heating chamber. So even the slightes amount of beryllium dust would end up in the food.- Also there would be special disposal procedures for microwave ovens similar to asbestos.The only reference I could find is here:http://www.repairfaq.org/sam/micfaq.htm#micmotQuoteSo I would assume that no modern consumer microwave oven uses beryllium oxide. Maybe some very high power industrial or really ancient ones.

author: chris_leyson
author_rank: Super Contributor
timestamp: June 13, 2017, 01:16:57 pm
content: Some specialist magnetrons may contain BeO but I've never seen one. The antenna insulator is most likely ceramic. In any case tubes or valves with conduction cooled BeO anode blocks would cost a small fortune and come with a whole bunch of warning stickers. 8560A and 4CS250R are two conduction cooled tetrodes similar to the air cooled 4CX250B.