Kenmore Microwave Oven - 2 failures in 2 years

Well what would you rather have, a magnetron gone wild, stuff being heated to the point of fire or a shorted diode blowing a fuse? I was taught in seminars by factory representatives never to exceed the ratings of parts if we had to use subs. And to always use factory supplied parts first. Do I feel this practical every time? No. But I tend to trust those that designed the equipment first. Does that mean your microwave is going to blow sky high or melt down if you replace the diode with one that has a 25% increased rating? I doubt it. Would I suggest you exceed the factory ratings on any part? Not where public safety including children are concerned.

Agreed. Sorry about the profanity, worked on too many CB radios back when the boom was on and truckers would drive hundreds of miles to our shop. We liked to make them feel at home if you know what I mean.

Do you really think that the OEM for the HV rectifer only ships units that break down exactly at the rated voltage? It is the minimum rating, and often the rectifier will handle the 25% you're complaining about. The original rectifier may have been able to stand 100% more PIV than the guarantteed voltage

The transformer will saturate if the line voltage is too high. Anything that increases the load current will blow the line fuse.

What 'I' would rather have is a technician that actually understands the circuit they are working on instead of one who makes mindless rants.

That is a nice set. It is on sale for $5.99 right now.

I haven't found any low grade bits in the HF set I bought a couple years ago. At one time Torx was considered a security bit, but they became mainsteam and ruined that. I like that there are duplicates. That way if you lose on on a jobsite you should have a spare. :)

Also, HF calls Torx either tourqe or star.

Did you know that HF had an assortment of 1/2W 5% carbon film resistors at one time? It was a nice starter kit for newbies.

Believe it or not I went to a branch last week and they had no knowledge of these bits!

We're now digging up my septic tank, so I'm in the correct frame of mind to discuss such issues. Both my arms ache from shoveling (I'm otto shape). Typing hurts, so I'll be brief.

That's a rather limited selection of options. I don't think any of those apply to a change of diode rating. What might apply is if a diode failure is used as a crowbar to blow the breaker or fuse. It might also be used to protect the maggot-tron by sacrificing itself before something else blows up. I doubt either of these are true.

Please note my previous comment that "such safety is for those that don't understand how things work". If the OP were a clueless idiot, with no electronics experience, no test equipment, and no understanding of the hazards involved, my advice would be to replace everything with manufacturer approved stock components. If the OP had some idea of what he was doing, has some electronics repair experience, and maybe owns a DVM, I would suggest that some substitution might be tolerated, but to check with the experts first. If the OP were able to design a microwave oven, understands exactly how it works, knows what a damper diode does, and is safety conscious, then I would suggest making all manner of radical circuit modifications. After reading how he extracted the Torx security screws, I consider the OP in the first category and somewhat regret suggesting a substitute part.

I got the same lecture when I was fixing consumer audio/radio/tv from the various manufacturers. However, it wasn't a safety issue. It was to avoid litigation based upon "unsafe" substitutions. The company will honor the warranty after repairs only if the repairs were done with approved parts. Substitute or modify, and the warranty is lost. It's bad enough when customers attempt to fix their own equipment, and then return it under warranty. It would be really bad if that were done by a factory authorized warranty station. More simply, customers can substitutes, while factory repair stations cannot.

I've never designed a microwave oven, but I can tell you how it works in consumer electronics and marine radio. At some point, early along the design cycle, the design is frozen. A major modification to one radio turned into a 12 week design cycle, but my initial design was frozen after only 2 weeks from start. I was finding errors all along the way, but was not allowed to make any changes for fear of introducing delays. Near the end, production required some changes, which was where I snuck in some changes. There were also some changes inspired by the dealers, as inspired by customers, and delivered through marketing. On occasion, there have been cost cutting exercises, which is another opportunity to fix things. Something like "We can cut $0.0001 off the cost if we switch to a diode rating that closer to the failure point. The savings, over millions of units, will offset any increase in dealing with failures".

Today, things are done quite differently. There's usually no breadboarding and the design cycle is MUCH shorter. The design is simulated on a computah, there's no breadboard, and it goes directly into production. If there are any problems, the standard answer is that the replacement model is already in the pipe and to wait for the replacement, and not fix the defect.

About the only thing that prevents total disaster is that most new products are evolutionary, not revolutionary. Changes tend to be small and earlier mistakes tend to eventually get fixed. However, my adage of "features and functions get added faster than bugs get fixed" also applies, thus keeping quality just above adequate.

So, you may trust the designer, but I wouldn't exactly trust the design.

Could that mean you agree with me?

Not public safety or children. Think certifications, litigation, liability, and tort law. For example, it's not UL or FCC certified if ANY component changes were made (without applying for minor change recertification).

I got my start in RF doing CB radios. I designed two CB radios, a CB pager, a mess of accessories, and worked for radio shops that did mostly commercial, but also some CB. Yeah, profanity is part of the culture. I managed to pickup a few choice words and phrases in high skool that have been difficult to eradicate. At least I've purged them from my writing. If I want to be abusive, there are other and better ways.

Read the disclaimer on their website: Not available at all locations. If they don't sell well at a particular store, they are discontinued at that location.

Some times the best way to blow off some steam is with words.

I worked for a commercial radio shop back in the 80s and designed a paging system for Timken Roller Bearing's two lines of equipment and the journeymen responsible for their continuous operation. I've helped design one of the best amateur radio repeaters in the Cleveland/Akron area now being used for the backbone of NOAA - W8CLE and SKYWARN.

Yep. I've learned more about effuent terminology and profanity while working on the septic system than all the CB lingo in my chequered past.

Well, working backwards, I either built or helped build: W6JWS-2m Bonny Doon. (no photos) K6BJ Santa Cruz. KI6EH Watsonville. (no photos) A bunch of junk in Smog Angeles I would like to forget. WB6EEP West L.A.

and a bunch of commercial stuff.

My favorite was a repeater built into a hollowed out 4x4 fence post and installed in a prominent location. Sorry, but no photos.

The problem with ham repeaters is that they seem to run forever, usually with zero maintenance. When something finally breaks, I get to fix it. When someone builds it wrong, I get to fix it. When something blows, I get to repair it.

Design is usually done on the back of an envelope. Documentation? We don't do no stinkin documentation:

One of the few smart things I've done is to NOT build my own repeater.

Heh...septic systems suck. I've lived in two homes with them in my youth and 5 kids in the house. #1 back in the mid 60's used to fill up and leak through the ground. Made the grass around it nice and green though :) #2 was in a home newly built for us in 1968. A brick ranch out in then rural surroundings, no water/sewer. Never had a lick of problems with that thing. It was a huge tank and cleverly made leech bed from house block in sand and rock. I guess in that location the tank could be made from house block and act partly as a leech bed of its own. 20 years later they ran water and sewer and caved in the tank and leech bed so I know what it looked like.

Well now adays using a prebuilt from a company like Icom, a cavity duplexer and adding a Mirage repeater amp and a couple Diamond Super Stationmasters, some 9913 or hard line is the way to go. Back in the early 90s it was piece together a controller, mobile or bass rig, an AT computer to handle the phone patch etc.... I know of one such beast still in existence that I had a part in its equipping and that I had modified a couple Motorola 160mhz "Pageboy" pagers for use on the repeater. It's used every day all day long and part of the SKYWARN 2 meter network. I can hit it with a 5 watt HT 50+ miles away albeit strategically located.

'90s? you should have tried building one in the late '60s. Motorola Twin-V transmitter strip, a GE Pre-prog reciever strip, home brew power supplies, Unijunction transistor timers and a surplus W.E. Touch tone decoder and a homebrew phone patch. The diplexer was home brew out of scrap copper pipe. All of this mounted in a surplus 3' shallow relay rack.

There were no computers. It was on 146.01/146/61 and installed in the pressbox at Lemon Monroe high School in Monroe Ohio. You could hit it from the Dayton hamfest with a 1 W handheld.

Yeah but I don't know where Monroe is.I have a close friend who still runs a modified Motorola Land transceiver on 2 and a GE (I think it's a GE) on .70cm. Plus we used to mess with a couple all tube 1200mhz transmitters yanked from an old Bell microwave relay station tear down. Had a ham friend who would get on the local repeater and announce where and when he was closing down a relay station and we could rip out most anything we could haul away. I still have boxes and boxes of all sorts of weird Western Electric parts, vacuum relays, tubes, waveguid for 1.2ghz and 1.6ghz, detector diodes, copper grounding strips and just about anything else you could think of made back in the 50s and 60s.

Feh. My first repeater:

was like that. 6m Pre-Prog receiver near the bottom. Unichannel receiver hanging in back. Two 80D xmitters, with mobile power supplied modified for AC operation, near the top. DC wire line remote in the middle along with home made control and audio panels. Note how cleverly I put all the heavy stuff on top so that it would topple when moved. Driving around town with a 2500 and later a Princess (Schmoo) phone on the floorboards was the ultimate in cool in the late 1960's.

Also, initially no touch tone. It was controlled by a rotary stepper switch and a single tone decoder. Also, no PL. A later machine used a Strowger switch when 10 functions were deemed insufficient. However, it was way too big and and made far too much noise, so a WE 247B materialized and I switched to Touch Tone. The first PC I used in a repeater was for IRLP, not the controller. I keep wanting to build and write code for my own PC based controller, but can't find the time, excuse, or market to justify the effort.

One of the repeaters I listed (W6JWS-2m) is an Icom RP-1510 commercial repeater owned by the local ARES group. I inherited the unpaid lifetime maintenance contract on it when the previous tech died. I had to remove a tangle of modifications, fix a few things, retune, and deal with a nasty case of intermod at a new location. The quality of the radio and controller are marginal, but it will probably remain in service forever.

How we got from microwave ovens to this will remain a mystery.

Back to shoveling mud and muck. Yech.

Interesting discussions :-)

If we may return to the original topic for a moment, I reassembled everything and now there is a loud hum. so I guess another component was busted when the diode went.

Any suggestions? I know there is some info above and I'll look for it later today.

Thanks to all for your patience.

Yep. Topic drift is so much fun.

My guess(tm) is that either the magnetron or the HV cazapitor are shot. I'm surprised the fuse or circuit breaking didn't blow. The hummmmm you're hearing is the transformer trying to pass way too much

Please be careful when poking around the HV cazapitor. There's no warranty on your life.

The 0CZZW1H004C cap is $26 from Sears. The 6324W1A001L magnetron is about $70. (Plus tax and shipping). You'll find these somewhat cheaper from discounters and ebay: