I paid $47 in 2003 at Sam's Club for my Sharp Carousel.
Amazing that it's still like new.
Yes, that's what I also encountered and described in #5.
Our microwave appears to have been an expensive one. Almost 30 years old, but quality built in Germany by Siemens. No Chinese (or similar) crap. Otherwise I wouldn't have been even tinkering with a repair.
Best regards!
Considering that a typical microwave oven has an internal fuse rating of at least 10 amps, sometimes even more, it's not a surprise that a circuit breaker would trip from the instantaneous and extreme current peak.
That also happens If the transformer is not turned off a 0 current by the triac.
A huge back EMF voltage spike will arc over the fuse.
Such as when a capacitor shorts while charging.
A huge back EMF voltage spike will arc over the fuse.
Such as when a capacitor shorts while charging.
The odd looking power supply is a full wave voltage doubler with the magnetron tube itself acting as the second diode and the load. The second cap is omitted. The capacitor forms a series quasi - resonant circuit with the secondary inductance in the transformer. This serves to limit the power consumed if the oven is operated empty or otherwise overloaded by detuning the resonant circuit, creating a high impedance, thus avoiding burnout of the tube. For this reason, the capacitor must be replaced with one of the same value, or close. Your 0.85 or 0.9 uF caps will probably work. The operating voltage across the tube is in the 3 to 4 KV range depending on the oven's rated power. This voltage is reached only on one peak of the input sine wave, so any common meter will read a lower than true voltage. If the oven puts out about 1 KW of RF power at 2.45 GHz, the DC input to the tube must be in the 1400 to 1800 watt range. This can kill you dead, then cook you to a crisp if it gets hold of you.
The capacitor in our Samsung / GE would definitely hold a charge. I did the usual screwdriver discharge and got a very visible and audible snap, but it alone would probably not have been a lethal shock. Note, there was no charge when the oven was run with the magnetron connected. It did however have a large charge when it was run with the magnetron disconnected. Thats where I got the discharge sparks.
Unlike most vacuum tube circuits, the magnetron tube operates with the plate grounded and a high negative voltage is applied to its heater / cathode. The common construction of a magnetron tube requires the plate, which is also the resonant cavity, to be grounded.
Our Samsung built GE branded "1100 watt" oven died. It did not blow the fuse or trip a breaker. It just made a loud buzz when you tried to operate it. The magnetron tube was dead, literally. It measured 0 ohms from filament to plate. I replaced the diode at the same time since it was cheap insurance and had been subjected to severe overload.
The capacitor in our Samsung / GE would definitely hold a charge. I did the usual screwdriver discharge and got a very visible and audible snap, but it alone would probably not have been a lethal shock. Note, there was no charge when the oven was run with the magnetron connected. It did however have a large charge when it was run with the magnetron disconnected. Thats where I got the discharge sparks.
Unlike most vacuum tube circuits, the magnetron tube operates with the plate grounded and a high negative voltage is applied to its heater / cathode. The common construction of a magnetron tube requires the plate, which is also the resonant cavity, to be grounded.
Our Samsung built GE branded "1100 watt" oven died. It did not blow the fuse or trip a breaker. It just made a loud buzz when you tried to operate it. The magnetron tube was dead, literally. It measured 0 ohms from filament to plate. I replaced the diode at the same time since it was cheap insurance and had been subjected to severe overload.
Thanks for the hint! Did it, and it fortunately proved okay. Never would have expected an isolation fault right here.
Btw, I'm scratching my head why the guy in the video used screw terminals to join the heater RF chokes with the terminal lugs instead of soldering. Is a solder joint in a magnetron unreilable?
Best regards!
Actually it is one of most common failure mode. Joints from chokes to terminal are usually spot welded, but a few I repaired gave no problem being soldered.
Success! Yesterday I received a 0.9 µF replacement capacitor, installed it and the unit works again now. Despite of and without neglecting the relevant safety concerns given above, I think it is true DIY spirit to keep an appliance alive instead of replacing it immediatiely. It also helps to avoid, or at least reduce, landfills 😉 .
Best regards!
Best regards!
Oh yes 😱😱😱!
Admittedly, I've already been thinking of such a device to annoy those lads driving in their cars with loud boom-boom music 😉.
Best regards!
Admittedly, I've already been thinking of such a device to annoy those lads driving in their cars with loud boom-boom music 😉.
Best regards!
That video remind me of a daft thing we had at work around 35 years ago. It was called an 'xyzabc123 detector' (substitute the name of your area manager) and was a polystyrene head and helmet full of neons placed in the microwave. When the boss was seen in the vicinity the microwave was started as a warning 😀
Yes, there are many vidoes on YT showing silly, but astonishing effects that may occur when you put things into a MOV. The contrast is, though, that the guy holds the magnetron outside the device 😱 .
Best regards!
Best regards!
NOT AT ALL
The 25kV picture tube supply is a couple mA at most, if that much.
The Microwave oven supplies "much lower" voltages, "just"a couple kV 😱 , but supplying around 1 KW (do the Math) when working properly and probably way more in a burst while frying you.
https://www.washingtonpost.com/nation/2022/04/26/fractal-burning-tiktok-wisconsin-died/
TV supplies will never do this while a microwave oven will, any day of the week.
Here Doctors injected "fluorescent" (radioisotopes) liquid into patient´s circulatory system: "bright" shows more or less blood is flowing; "black" means NO blood circulation, period, so those areas will die and gangrene, requiring amputation.
Sadly those hands have no future.
Sorry for the disgusting pictures but feel here they are justified because of the inherent danger present in oven HV supplies.
Extend that to some wild projects that surface now and then in this very Forum using transmitting tubes with matching kV range supplies.
Not too worried about electrostatic speakers since the very word "static" implies very low currents, but I have seen a couple "direct drive" projects using multi kV tubes direct feeding them ... which require the matching multi kV supplies.
Oh well.
In the case of an electrostatic loudspeaker with a step-up transformer rather than a direct-drive amplifier, the high voltage supply for the diaphragm is usually not very dangerous because it is designed to deliver almost no current, but the secondary side of the step-up transformer that drives the stators is quite dangerous when loud music is playing.
If you were talking to me: As already written four weeks ago, the oven works again just after I replaced the shorted capacitor.
Best regards!
Best regards!