Microwave bad magnetron? - Page 1
Forum section: electronics / repair

author: canadaboy25
author_rank: Regular Contributor
timestamp: November 11, 2018, 03:56:05 am
content: Hey guys I have a Panasonic microwave with an inverter that isn't heating. The microwave runs for about 20 seconds, stops, and displays an error code. I followed the service manual steps to check the inverter and seem to have come to the conclusion that the inverter was ok. However, I wasn't convinced so I unplugged the high voltage wires from the magnetron and jumped them with a very thin strand of wire from a multistranded cable. Immediately after starting the microwave it vaporized the wire. This is a repeatable result so it seems the inverter is in fact good.This would suggest that the fault is in the magnetron. However, the filament in the magnetron tests good at 0.2 ohms so it seems strange to me that it would be causing the problem.Just wondering if anyone here knows anything about microwave repair and could let me know if replacing the magnetron is the right call or of there is something else that could be the problem.Thanks

author: amyk
author_rank: Super Contributor
timestamp: November 11, 2018, 04:06:58 am
content: The fact that the inverter can output for a brief period of time doesn't mean it can hold its output continuously. What's the exact error code?You can check if the magnetron has a short between the electrodes too; checking if it's lost vacuum is much harder, however, but in my experience the magnetrons are reliable and the inverter is usually the problem.

author: xavier60
author_rank: Super Contributor
timestamp: November 11, 2018, 04:48:58 am
content: Quote from: canadaboy25 on November 11, 2018, 03:56:05 amIn case of someone not knowing. Placing a thin strand of wire between the ends of the 2 thick red wires is only loading the low voltage filament supply. The actual EHT supply of over -4000 volts is present common mode between the red wires and chassis.Btw, when magnetrons test short from the pins to frame, the short is likely to be in the socket base. There are feed through capacitors built into the socket base that can break down.

author: canadaboy25
author_rank: Regular Contributor
timestamp: November 11, 2018, 05:37:54 am
content: I had forgot to test between the filament and the shell. Just tested it and it shows 180 ohms of resistance between the pins and the housing.It is showing error h98

author: james_s
author_rank: Super Contributor
timestamp: November 11, 2018, 06:03:22 am
content: That doesn't seem right, IIRC the filament and shell should not show any continuity.You could try borrowing a magnetron out of another microwave, I've swapped them a few times, using magnetrons from junk ovens to fix others, generally if it's close enough it will work.

author: xavier60
author_rank: Super Contributor
timestamp: November 11, 2018, 06:20:50 am
content: Quote from: canadaboy25 on November 11, 2018, 05:37:54 amIt is possible to check further by removing the cap and cutting the choke wires away from the socket base's internal pins.

author: canadaboy25
author_rank: Regular Contributor
timestamp: November 11, 2018, 06:57:49 am
content: Quote from: xavier60 on November 11, 2018, 06:20:50 amSo you're suggesting it could be shorting here?

author: xavier60
author_rank: Super Contributor
timestamp: November 11, 2018, 07:00:57 am
content: Quote from: canadaboy25 on November 11, 2018, 06:57:49 amYes, I have seen a few. Cut the wires close to the socket pins.

author: canadaboy25
author_rank: Regular Contributor
timestamp: November 11, 2018, 08:16:47 am
content: Quote from: xavier60 on November 11, 2018, 07:00:57 amOk, so with the wires cut, there is no continuity between the filament and the case. One of the pins passing through the housing has multiple megaohms of resistance to the case but the other pin was the one causing the issue like you thought because it has around 190 ohms of resistance to the housing.This would case a no heating fault?

author: canadaboy25
author_rank: Regular Contributor
timestamp: November 11, 2018, 08:38:32 am
content: Well i jumpered the wires from the magnetron to the inverter and the microwave heated just fine but now when I try to repeat the results I just get a small zip sound from the inverter area and the microwave stops...However after a small cooldown it will work again. While running there is what sounds like vary faint arcing-ish sounds coming from the same area.

author: xavier60
author_rank: Super Contributor
timestamp: November 11, 2018, 08:44:09 am
content: That 190 ohms would drop to something even less when the inverter tries to apply -4000 volts to it. That is definitely the cause of the oven not working.

author: xavier60
author_rank: Super Contributor
timestamp: November 11, 2018, 08:45:47 am
content: Quote from: canadaboy25 on November 11, 2018, 08:38:32 amDon't do that. There is likely to be microwave leakage.

author: canadaboy25
author_rank: Regular Contributor
timestamp: November 11, 2018, 08:53:58 am
content: What do you suggest for a repair besides a new magnitron if it isn't possible to jumper it?

author: xavier60
author_rank: Super Contributor
timestamp: November 11, 2018, 08:57:28 am
content: Quote from: canadaboy25 on November 11, 2018, 08:53:58 amI'm getting worried now. I didn't expect you to jumper it or what you are likely to do next.Best to replace the magnetron.

author: canadaboy25
author_rank: Regular Contributor
timestamp: November 11, 2018, 09:02:46 am
content: Quote from: xavier60 on November 11, 2018, 08:57:28 amNo offense intended but if there is no way to repair it why does it matter if it was an internal fault in the first place? I may not have experience with microwaves but I have experience with much higher voltage systems and know how to be out of harm's way before trying something potentially dangerous.Since you suggested that it was only an external fault on the magnitron you obviously have repaired some in the past and I'd greatly appreciate if you'd share your experience with me.Thanks

author: xavier60
author_rank: Super Contributor
timestamp: November 11, 2018, 09:12:41 am
content: Ok, I feel better about this now.I have replaced the faulty sockets with ones pulled from other discarded magnetrons where the socket is still good.I leave about 10mm of wire attached so that a good mechanical connection can be made to the choke wires by either twisting them together or binding them together with a strand of wire then soldering. The enamel has to be scraped of first.The flange part needs to be firmly attached to the cage with screws.

author: xavier60
author_rank: Super Contributor
timestamp: November 11, 2018, 09:16:59 am
content: EDIT: I deleted the first link I posted because it looked like the socket had a non-metallic flange.https://www.aliexpress.com/item/4Pcs-Lot-New-Microwave-Oven-Magnetron-Accessories-Launch-Tube-Socket-Heating-Tube-High-Voltage-Filament-Plug/32878524445.html?spm=2114.search0604.3.15.231d5e77gKc68g&ws_ab_test=searchweb0_0,searchweb201602_2_10065_10068_10130_10547_319_317_10548_10696_10924_453_10084_10925_454_10083_10926_10618_10920_10921_10922_10307_10923_537_536_10131_10132_10133_5733215_5733315_10059_10884_5733115_10887_100031_5733415_321_322_10103_5733515_5733615,searchweb201603_51,ppcSwitch_0&algo_expid=8d831b15-cb01-4583-b362-fe525db37e24-2&algo_pvid=8d831b15-cb01-4583-b362-fe525db37e24

author: james_s
author_rank: Super Contributor
timestamp: November 11, 2018, 06:14:09 pm
content: I bet you could take the socket out and replace it with some crimp spade connectors and squirt a blob of silicone around to hold them. Ugly but functional, and if it's already defective there isn't much to lose.

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 11, 2018, 07:12:03 pm
content: I've repaired a few dozens of microwave ovens including ones with bad magnetron's, I have never been curious enough to break the filament connector though.I'm guessing it could contain low value high voltage capacitors, forming a LPF with the 2 chokes to keep the RF safely in the shielding.Can anyone confirm?

author: xavier60
author_rank: Super Contributor
timestamp: November 11, 2018, 09:08:47 pm
content: I measured the capacitance of some disassembled magnetrons and got readings of about 300pf per pin.The big unknown is how much microwave leakage this capacitance prevents and if the cheap replacement sockets contain capacitors.I have ordered some very cheap ones on ebay for testing.

author: hermit
author_rank: Frequent Contributor
timestamp: November 11, 2018, 10:31:20 pm
content: Magnetrons rarely go bad via open filament. The most likely thing is actually mechanical deformation. I worked on them for years and diagnosis was more of a sound thing that you pick up with experience.

author: james_s
author_rank: Super Contributor
timestamp: November 12, 2018, 02:11:19 am
content: I wouldn't worry too much about microwave leakage. Obviously it should be minimized but the whole thing is inside a metal cabinet so even if you left the filter out entirely it wouldn't be dangerous although you might knock out WiFi reception in your house.

author: xavier60
author_rank: Super Contributor
timestamp: November 12, 2018, 02:18:59 am
content: Quote from: james_s on November 12, 2018, 02:11:19 amI don't think there will be harmful leakage. There could be enough to interfere with the workings of the electronics.Keeping in mind that it didn't function properly with the socket removed.

author: hermit
author_rank: Frequent Contributor
timestamp: November 13, 2018, 04:24:33 pm
content: Microwaves can't leak out from the screen mesh in the door because the holes are too small. I've heard they are 'way to small'. So, you can use that as a rough guide.

author: tehmagicsmoke
author_rank: Contributor
timestamp: November 14, 2018, 06:54:04 pm
content: Start with the basics. Most microwaves have 3 door switches. I've repaired a couple microwaves, and that was the cause. Then I'd suspect caps.

author: jmelson
author_rank: Super Contributor
timestamp: November 14, 2018, 09:48:14 pm
content: Quote from: canadaboy25 on November 11, 2018, 05:37:54 amThat indicates the magnetron is shot. It has developed a whisker of metal bridging the cathode (terminals) to the anode (main housing).Or, possibly, the feedthrough caps have shorted.Jon

author: Gyro
author_rank: Super Contributor
timestamp: November 14, 2018, 09:57:24 pm
content: Nobody (well last two posts) seems to be reading back to see what has already been established in the thread anymore.

author: floobydust
author_rank: Super Contributor
timestamp: November 14, 2018, 10:15:19 pm
content: Panasonic Technical Guide for Inverter Microwave Ovens which has a repair/troubleshooting flowchart and inverter schematic. I found it here:http://media.datatail.com/docs/manual/371449_en.pdf

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 15, 2018, 07:31:53 am
content: Quote from: Gyro on November 14, 2018, 09:57:24 pmTechnicians no longer read, they just replace parts these days.

author: xavier60
author_rank: Super Contributor
timestamp: November 29, 2018, 12:14:16 am
content: The new magnetron sockets arrived. They look to be good quality and measure 440pF per pin.I used one to repair a 2M261-M32.I overlapped the cleaned choke lead with the pin, wrapped 2 turns of 24awg solid around it and soldered.Ill report back if I put the magnetron into service.https://www.ebay.com.au/itm/5Pcs-Electronic-Microwave-Oven-Magnetron-4-Filament-Pin-Sockets-Converter-Home/132568014524?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

author: chimerahitman
author_rank: Contributor
timestamp: January 29, 2019, 01:12:45 am
content: How did it go?I just had mine, LG MS1596CIR, go bad as well. It just stopped working full time.Sometimes I'd place something to heat, and it would just spin without heating. I'dand place it again and this time the microwave would function. I later confirmed the behavior by looking at the input power with a Kill-A-Watt device and see that about 300W were being used, and on the time it would work it would hit about 1800W. This is on a 1400W microwave.I will be taking a look at the operation without the lid on since I hear strange zit zit noises intermittently. I'd bet on the inverter board going out because of some power outages I had a few weeks ago.EDIT: Forgot to mention it's a Inverter microwave oven, though if you search the model # it'd show it to be so.

author: james_s
author_rank: Super Contributor
timestamp: January 29, 2019, 01:14:59 am
content: That sounds more like a bad connection than a bad magnetron. Only way to know is have a look inside.

author: soldar
author_rank: Super Contributor
timestamp: January 29, 2019, 03:08:39 pm
content: I have repaired quite a few microwave ovens over the years.If the transformer is getting voltage then there are very few parts to test, just four. By frequency of failure I would say (1) is the HV diode, (2) is the capacitor (3) is the magnetron and (4) the transformer.It is really simple to check each part. Most of the time it is the diode.

author: coppercone2
author_rank: Super Contributor
timestamp: January 29, 2019, 05:20:33 pm
content: You know im glad my microwave broke and i got a magnetron from it. And the new one does not have a godawful beeper circuit or clock on it.Eliminating the blinking clock was more then enough.And it had all sorts of problems. Overheated crimps, shady microswitches, etc.Built like garbage.What the fuck is the clock for? To remind you that your gonna get fat eating at 3am? Or to just blink 12 constantly?? God damn parasitic clocks.

author: janoc
author_rank: Super Contributor
timestamp: January 29, 2019, 06:19:17 pm
content: Quote from: coppercone2 on January 29, 2019, 05:20:33 pmIf a microwave has clock it will likely let you program a start for a certain time - so that when you wake up or arrive home you will have your food warmed up already. Or at least that was the idea, I think.

author: coppercone2
author_rank: Super Contributor
timestamp: January 29, 2019, 08:28:42 pm
content: Quote from: janoc on January 29, 2019, 06:19:17 pmholy shit I had no idea I can do that. I am serious. For some reason using the microwave on a timer never occurred to me.But what food can you cook that way? Unless your making potatoes in the microwave (not bad actually if you figure out how to do it), what do you trust to leave on the counter for hours? I guess its not a bad idea for a vegetable cooker since they are more nutritious from a microwave then other cooking methods.If someone made a peltier cooled insulated microwave that can store a soup or bacon or something in it that would be more useful IMO.

author: janoc
author_rank: Super Contributor
timestamp: January 29, 2019, 10:05:01 pm
content: Quote from: coppercone2 on January 29, 2019, 08:28:42 pmI am not sure I would leave raw food in a microwave overnight so that it can be cooked in the morning but there is plenty of food that you just warm up (no need to cook it). Also you don't need to necessarily use it overnight but maybe an hour or two delay while you are shopping, for ex.But you can certainly cook rice or pasta in a microwave. Or even make coffee if you are desperate. None of that would spoil.I would be more concerned with leaving the microwave unattended but some people don't have qualms about it.

author: coppercone2
author_rank: Super Contributor
timestamp: January 30, 2019, 12:07:48 am
content: how do you get the water and pasta not to mix?You mean like a non-meat pasta reheat?

author: janoc
author_rank: Super Contributor
timestamp: January 30, 2019, 02:30:12 pm
content: Quote from: coppercone2 on January 30, 2019, 12:07:48 amhttps://www.thespruceeats.com/spaghetti-in-the-microwave-481882But I think we should keep the discussion to the topic and not microwave cooking recipes.

author: coppercone2
author_rank: Super Contributor
timestamp: January 30, 2019, 05:16:29 pm
content: I dont see anything in that recipie that can be left in the microwave for many hours...You can prob make potato chips good that way though. You just need a stack and some tuning.I guess if you just leave for a few hours its alright. I am stuck thinking of a ten hour work day.

author: canadaboy25
author_rank: Regular Contributor
timestamp: March 07, 2019, 11:23:29 pm
content: I ordered a connector on ebay an and waited the 3 months that they quoted it to arrive and it never did. They refunded my money so I guess I'll try my luck ordering another one.

author: oolloo
author_rank: Contributor
timestamp: May 06, 2019, 07:48:41 am
content: Quote from: tehmagicsmoke on November 14, 2018, 06:54:04 pmThey can but they don't lol here's how to know for sure. Go look at a old Cband only mesh satellite dish , they receive at 4ghz a microwave signal. Not at the same power though.However thier job is to not allow any microwave signal to penetrate through, rather to reflect microwave energy back into the feed horn.We all know the higher the frequencies the smaller the wave, that's why your uhf and vhf tv antennas are huge or have huge dipole. Inside a C band feedhorn you'll find the dipole for reception of a 4ghz signal it's about 2 CM. (Sorry yanks , it's called metric, it's over 100 yrs old, time for you to catch up, stop using your barbaric biblical measurements .)Taking into account that no hole in microwave oven is greater than that of mesh on a 3 metre satellite antennaAnd that a 2.4 ghz signal like the one Panasonic magnetron makes . Also keep in mind that the USA allows 5 as a measure of leakage acceptable and Canada allows 1 where Australia allows 2. Not sure what the measure is it's in the Panasonic microwave oven repair guide though.ORAlso you could look at a 2.4 ghz Wi-Fi mesh antenna and see that the gaps are huge yet it still is a barrier to that frequencie.

author: OwO
author_rank: Super Contributor
timestamp: May 06, 2019, 08:26:42 am
content: A new magnetron costs about $5 here... it's just heavy and costly to ship.

author: coppercone2
author_rank: Super Contributor
timestamp: July 15, 2019, 07:02:02 am
content: if it has a whisker can't you blow it up with a high current pulse?