Microwave blow up and other electrical repairs!

[burger2227]

WARNING! Microwave ovens use HIGH VOLTAGE components! Do not touch larger wires EVEN UNPLUGGED!
The SHOCK may not kill you but it may cause you to STRIKE objects nearby causing SERIOUS INJURY!

The one time I go outside to toss some trash, I come back to an arcing microwave oven cooking a potato:

I had cleaned the interior earlier that day and when I removed the wave cover I found this!
The potato was cooked and I ate it later.

The magnetron had melted down and kept arcing until I canceled cooking:

The tip was destroyed and it had burnt a large part of the mica wave cover inside the cooking area.

2 screws on top in the thermostat bracket and heavy ground wire and one screw on the right side held the magnetron:

Watch out for the high voltage transformer and capacitor below! The cap can hold 5,000 volts unplugged!

Thankfully the other parts appear to be OK! I'm waiting on parts from Ebay now.

Sometimes all you need to replace is the mica wave plate, but this magnetron kept arcing after it was removed:

Two screws hold the top plate of the magnetron together so removing it allows access to the top magnet. Bottom one takes more effort.
Be careful removing the magnet! It is VERY STRONG and can pinch fingers on edges near any metal!

Here is the top magnet stuck to my refrigerator door. Hold it on the sides to place it on metal objects!

To remove it from steel surfaces you may have to slide it off an edge. It could damage finished metal surfaces!

The magnets are great for magnetizing steel screwdrivers or bits! It will hold them for you too...on refig door!

Also can be used to fish for metal objects, but may stick HARD to any metal objects nearby.

Once the wave plate mica and magnetron are delivered I will show how it is repaired... I fixed them for Sears.

[iamdenteddisk]

I got a bunch of these old magnets screwed to my electronics bench for snatch and grab tools. like the hacksaw or multi screwdriver, files.

i even put one on the wall right behind the bench to be able to toss screws from a project for safe keeping till i put it back together..

plus one down in the bench pan which is like a metal bottomed drawer. this catches little metal slivers i cut or that fall as i work. especially hot stuff this is good for. but it also helps to keep ferrous and non-ferrous metals separate. the benchpan's main task is catch molten or hot metals and not catch fire.
i seen plenty of mishaps in my time. once had to lay on a woman to put the fire on her out.

i still do some jewelery work at the same bench and the scrap gold is let loose in the bench pan while any iron can be lifted out like magic by magnet.

wish you didn't eat that potato man, from the damage on that magnetron, i would almost bet the missing metals from it, where infused into the potato.

drink lots of distilled water to remove it from your system!

[burger2227]

Not to worry! The arcing went straight to the side of the microwave and not the potato.
I was also able to heat up water, but the arcing forced me to cancel when it was warm.

The magnetron is already nearby so I should get it today. Priority 2 day mail as sent by seller.

The mica wave sheet is still in Ontario Canada.

[burger2227]

SAD STORY, the new magnetron arcs too so I guess the side metal is too far gone to use.

This is the used magnetron I got for $18 with 2 day shipping with the correct top mounting bracket:

Note how nice the rod looks compared to my old one...

Before I tossed it, I decided to see how easy it was to get at the turntable motor:

I used a pair of wire cutters to open the cover and reveal the motor.

The motor is 120 volt AC 60 hz and 3 RPM:

It may come in handy some day and they are worth at least $10.

The motor turned the turntable in each direction alternately every time it was used:

I also kept the wire connector.

Now I gotta buy a new microwave and sell the used magnetron I did not need.

[iamdenteddisk]

the arc is probably a a large diode or bridge rectifier that has broken down. allowing the wrong polarity to be present. it's usually what causes this "damaging arc effect", my experience with microwave ovens is it's best to junk them out get a newer one. for best results..

I do have a really good book on appliance repair that covers them. I have fixed a few but they are so dangerous they are not worth trying to repair.
if you fix one mechanically it is still possible to have radiation leaks which can nuke your nuts at a distance. and worse. considering many take medicines like lithium which leave metal deposits in the brain<- I would think this and dental work being the worst possible reaction scenario..

the oven worth maybe $100-$200 new or $20 used, i know human life has got to be 5-6 bucks now days but metal matchbox cars are priceless and they may be endangered...

in truth I wouldn't save much more than magnets when junking one because of the danger involved in high voltage projects and radiation..

[burger2227]

Naw the high voltage diode would not cause the arcing. The old magnetron burnt up the side metal and GE recommends just tossing them. I figured I'd just give it a shot with a decent one and if it didn't work I can sell it again on Ebay.

The only reason I wanted to fix it was that I liked the way it entered times with a crank knob instead of a keypad. I paid about $160 for it 10 years ago.

I have two $50 gift certificates I can use at Best Buy. Most of the ones at Walmart are under $100.

[iamdenteddisk]

thumbs up!

[burger2227]

Well my problems aren't over as my new microwave has no light when the door is open and the keypad is too dark to see also.

I have some one AA battery 4 LED keyhole lights that are motion sensitive to play with so I mounted one above the keypad.

A TicTac box serves as a temporary mounting bracket holding the keyhole light above the keypad with black Velcro strips.

Keyhole LED lights on Ebay for $3 to $5:
http://www.ebay.com/sch/i.html?_from=R4 ... D&_sacat=0

The keypad and door opener button are directly below, so any motion there turns the light on:

You can see the top of the door button and the room was dark when I took these pictures.

There is enough light to even see inside of the oven:

It turns on when I walk by sometimes, but I've had rechargeable batteries last longer than a month.
The LED unit slides up a back plate to get to the AA chargeable battery to replace it easily.

We'll see how it lasts and perhaps I may go inside and see if I can rewire the light bulb.

Here's my review on Amazon: http://www.amazon.com/review/R1TW2E1J6V9CGY

[burger2227]

GOOD GRIEF! The LED light fell off and broke! Tried to fix it, but I didn't find anything wrong with it electrically.

So I put another one on with better tape. I added a clear blinder to keep it off, but had to add a paper blinder for walking by...

Not pretty but functional!

[burger2227]

Wireless Doorbell

My old wireless doorbell quit working so I got another one. Today I finally got to look at it and figured
it had to be a diode or two in the bell sound box that plugs into the wall... it was completely dead!

Checked the two black 1N4007 main rectifiers with an ohm meter and one end unsoldered from board
and both appeared good. They are near the 100 volt AC prongs to make DC voltage out of it.

Checking the two glass diodes the same way said both were bad when the meter's diode tester beeped,
so I took both out and each read 1N4737 or two 7.5 volt Zener diodes. Cost about 4 cents each:
1N4737 7.5 volt, 1 watt Zener diode

The Zener diodes create a steady DC voltage of about 7.5 volts for the bell circuit and louder sound.
Glass diodes may be very hard to read. I had to use a magnifying lens to read them carefully.

Well I already had a bunch of Zener diodes for other voltages so why not a 4.7 and 3 in series for 7.7 volts?

Up in the top left corner are the two replaced Zener diodes with each one's cathode in the same direction.
Zener diodes drop the cathode voltage to the rating above the anode voltage. Series adds the voltages up.
The odd voltage may be the reason they did not just use a normal 5 volt regulator instead of Zener's...

Note that the large 335J (3.3 uF 5%) 400 volt capacitor supplies a lower AC voltage instead of an
isolation transformer so there is high AC voltage potential at the circuit board level so do not
handle or plug the unit in backwards as 110 AC would be on the common of the entire circuit!
Metallized Film Capacitor CBB22 335J 400V 3.3uF

To calculate the current available from the 3.3 uF capacitor we can use the following QB program:

Code: Select all

'Inductive Reactance = 2*pi*frequency*inductance
'Capacitive Reactance = 1/(2*pi*frequency*capacitance)

DO
  INPUT "Enter AC supply voltage: ", voltage& '= 120
LOOP UNTIL voltage& > 0

ACfreq = 60 ' 50 'in Europe and Asia?
DO
  INPUT "Capacitor farads(1uf = .000001) or microfarads >= .001:"; capacity 'uF or less
LOOP UNTIL capacity > 0

IF capacity >= .001 THEN capacity = capacity / 1000000: PRINT USING ".############ farads"; capacity
Creact& = 1 / (8 * ATN(1) * ACfreq * capacity)
PRINT USING "Reactance = ########,.## ohms"; Creact&

current = voltage& / Creact&
PRINT USING "Supply Current = ##.###### amps"; current

The available current is .137 amps or 137 milliamps with Zener's possibly setting 7.5 and 15 volts supplies.

I also had to replace the two green speaker wires as the old ones fell off during repair.

[burger2227]

Tiger arc lighter repair. WARNING! HIGH VOLTAGE! Stay off the button!

The arc lighter started working when the lid was closed and the button was pressed, then quit altogether:

The lighter metal swich part fell out when I opened it by removing the bottom two small Phillips screws by the
micro USB plug. After removing them I had to pry the top part up with the prying tool in the crack below the lid
assembly. It took some effort at first.

Finally the entire internal assembly slid up taking the square Tiger button plate with it. It just lays over a small rectangular switch:

If you look closely below the yellow wire and to the left of the blue wire there is an L shaped metal bracket that
lost the end piece. The large black coil creates the high voltage arc, which may not shock you, but could burn you! Lithium battery is on left.

Placing a flat screwdriver between the angle and the screw to above it made the lighter work when the white button was pressed.

So I soldered a blob of solder to jump the space and checked that it was secure with a flat screwdriver.
The red LED is the charge indicator that sits in a white plastic mold next to the small white button switch.

Then I reassembled it by taping the wires down and placing the Tiger button plate over the white switch.

The cover has a slot on the front for the button plate to slide into while pushing it back up.

The lighter uses only a 402030 220 mah lithium battery with protector circuit
4 mm thick by 20 mm wide and 30 mm long including the protection circuit.
There are 2 solder pads on the bottom of the circuit board on side it is connected to for voltage checks.
Lithium 3.7 volt batteries should never read below 2.8 volts or they need replaced!
This is the same battery used in my new HD car camera that I had to replace with an 18650 one externally.
Ebay has them for $5 to $8 with free shipping from China or Hong Kong (up to 30 days)