The AM Forum

this could get interesting IF a schematic can be obtained .... assuming its a hv supply driving a magnetron .... could get handy

Here is one such schematic:

Phil - AC0OB

I had one, a Panasonic, about 2 years ago. Light weight! The magnetron arced on a few occasions once it was out of warranty and this destroyed the power supply. It should not have blown the supply, so I may have had a lemon.

I by coincidence am doing the full BFS prep on a pair of "matched" MOT's. I have verified voltage, knocked out the shunts after using a heat gun on each side to soften things a bit. Then a retest and fabbed spacers with sheared .062 FR-4 strips and pounded them in, Then I sealed them with poly. This will be the standard grounded CT with the fil windings aiding the primaries and all 4 windings effectively in series. This should with choke input, produce the 1000V I need.

looking at the schematic in figure 13 and noting the topology of the inverter, would it be right to say that it is not just a matter of reversing the diodes, but also reversing the polarity of the inverter transformer primary, so the duty cycle of the magnetic field goes the right way? the next part may be irrelevant, look at the schematic, looks like one diode polarity is drawn reversed from normal (probably D702). But it is worth to consider the effect of duty cycle vs. the polarity of a rectifier.

What I mean is that unless it is a 50% duty, the direction of the winding matters to the output voltage level for a given rectifier polarity. In other words

assuming a half wave rectifier circuit:
 94% ON time, diode set for negative output and conducts 6% of the time: -2000V @ 0.5A
 94% ON time, diode set for positive output and conducts 94% of the time: +112.8V @ 8A (which the winding could not handle..)

now swap the primary winding polarity so the short duty is in the positive direction..
 94% ON time, diode set for positive output and conducts 6% of the time: +2000V @ 0.5A
 94% ON time, diode set for negative output and conducts 94% of the time: -112.8V @ 8A (which the winding could not handle..)

Does this look right? It seems right based on experience with things from TV sets to other power supply-type switchers not driven by bridges but by a single switch.
I have even seen a horizontal output transformer winding with two opposite-facing diodes, one making +185V and one making -30V. The difference was the way the duty cycle faced, up or down so to speak.

Then looking at the real schematic in figure 14, it looks like the thing is a full wave doubler having both ends of th secondary above ground (below ground) and so the above may not matter regardless of how the diode is drawn. Is 4KV wanted? or 2KV?

Also, the DPC has to be tricked and there is that IC which is no part number given.
The unit stops if the filamet current is not detected, (page 15 steps 1-3, and probably when the magnetron current is wrong {low?} (steps 4-5)
Note C703 and C704 are different values. Could it be related to the expected average duty cycle? duty of 0.594 for one polarity and 0.405 for the other?
It does say what voltages are normal to IC701 and 702, but what if those are 20-40KHz waveforms or something else weird?

Anyone else study this?

My Wally special, Panasonic microwave is no friend to radio. It knocks out my VLF reception and our home WiFi.
Perhaps salvage isn't a bad idea  :)

Frits

Frits, 

A magnetron in a uWave oven self oscillates at 2.45 Ghz, and the usual WiFi frequencies (Channels 1-11) are just below that. Consider a 600-800 watt transmitter in your home, although well shielded, will have some leakage, and will pollute the WiFi channels with trash. Also consider that the uWave oven door seal might be compromised with crusty food junk.

I recently bought a USB high gain Wi-Fi antenna with a LNA built in. The thing literally picks up WiFi not detectable with my laptop built in antenna, and presents signals at 4-5 bars. The Amazon reviewers slammed the thing because it stops working when the uWave oven is on...To me that is no fault of the antenna..

Jim
Wd5JKO

Hi Jim,
Yeah, that is a great way of looking at it, having a shielded transmitter/antenna in the kitchen. All though I never had the WiFi problem with our older (heavier) uWave. The Panasonic probably has less shielding.
The VLF wipe out is no doubt contributed to the switching power supply.

Frits

Many years ago I repaired a radar detector for a co-worker.  When I was done, (hmm, now how do I check this?) I took it to the kitchen (with a 12 volt supply) and ran the microwave which set off the detector.

You can see/hear most microwave ovens with a receiver or spectrum analyzer at distances of 10-100 feet (maybe more depending on the condition of the oven and the antenna used). The ovens produce a nasty spectrum as the carrier wobbles around in frequency and is modulated by 60 Hz and harmonics thereof. They make Timtron's SBE rig look clean.  ;D

Mmm. Perhaps I should rethink my kitchen table setup, with my head a foot away from the microwave door. That's why I'm loosing my hair  ;D
..SBE rigs are cool, have you flipped your receiver to FM.. you be surprised

Frits