Kenmore Microwave Oven - 2 failures in 2 years

They are security Torx screws. There are also some that have one less notch than standard Torx screw heads.

Security Torx

Some of us do fencing for recreation. At other times, we answer questions on the internet. The skills required and entertainment value are fairly similar.

When the diode shorts, the transformer starts to suck LOTS of power. The eventual result is a blown fuse or breaker, but meanwhile, the high 60Hz current causes plenty of buzz.

Hold it. You haven't done any of the other suggestions. I'm still worried if the waveguide to magnetron connection is correct, if the window is properly attached, and if there's any evidence of arcing inside the waveguide. Something caused the diode to blow twice and you'll need to find the cause before blundering onward. Replacing the diode is just damage control. Since it has happened twice, it could also be a metal fabrication error. Look for the problem BEFORE you fire it up.

I would use the diode you just installed. They're cheap enough that you could blow it up without much worry. However, if it does blow up, then you'll have to find the cause, or the replacement, which is only

Those are 6 point Torx security screws. Bits can be found at the local hardware store or on eBay:

While you're at it, you should also get the 5 point variety. I had to do that to tear apart a Seagate USB disk drive enclosure:

If I'm in a rush, I grab the Dremel tool, insert an abrasive disk, and cut a slot across the head. Then, I just use an ordinary flat blade screwdriver to extract the screw. I recently had a situation where I couldn't do that, so I just used a die grinder and destroyed most of the screw head. I consider tamper proof screws an attractive nuisance.

Harbor Freight has several different sets of security bits:

Agreed. But I have a (Chinese, of course) set of Torx security screwdriver bits, so I use them. I save the Dremel + cutting disk technique for the /seriously weird/ screws.

Thanks.

I have the 100 piece set, which I bought at the local hardware store for about 3 times the price. It does NOT have 5 point Torx style bits, but does include some other weird bits. About 2/3 of the set are NOT security bits, but just common Torx, Allen, Phillips, straight blade, etc bits. There are also some duplicate bits that seem to have been added so that they total 100 bits. The quality of the supplied bits are kinda marginal.

I also have several of the 33 piece sets, which are all security bits. This is a good selection, but also do not include 5 point Torx style. The quality of the bits are much better than the 100 piece set.

The five point ones are often found in automotive applications and domestic electrical goods where there is an electrocution hazard. Though I have seen some with a triangular recess with a centre pin.

"bw" wrote in news:hbg4b6$g6m$ snipped-for-privacy@news.eternal-september.org:

Harbor Freight sells those bits.

On my Nissan sentra,I encountered two 5-lobed security screws,at first I thought it was the usual 6-lobed Torx.Fortunately,the screws had an integral washer that was thick enough for my mini-channellock pliers. the screws were on the Mass airflow sensor/housing.

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

Thanks for the link,Jeff! I could have used these a few weeks ago,on my Nissan Sentra SpecV MAF sensor.

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!

I was able to get the screws out by bending the center pins just enough to allow the hole-less Torx key to catch the 6 faces in the screw. Then I brought them to a strong vice and I flattened said little pins with a few whacks. Now I can do some real screwin' :-)

OK guys, I have installed the diode but I was unable to ?ind a wave guide. I have seen pictures of guides - a small channel to direct the waves. but I have no such channel, unless it is the short duct between the magnetron and the oven wall. On the inside of the wall there is a plastic plate about 5" x 3". The oven has a curved back inside. Presumably the waves get scattered all around inside. The inside is in pristine shape - I could see nothing like small burn holes.

My situation now is whether to try to start it up or start taking measurements. There is a small pamphlet with some measurement guidelines.

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.

That is the waveguide, AKA a duct to carry the RF into the oven cavity.

Take a look under the plastic plate for bugs or grease.

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.