This model 721.63252 301 has gone belly up for the 2nd time in 2 years. Both times it blew there was a pop, then a smell of overheated plastic and then a loud hum. I took it to Sears the first time and they replaced the diode. It then worked fine though it had very small usage.
Now is the second time and it is off the warranty. I opened up the oven case and quickly found the diode. It has the marker T3512 and H6N below it. One end of the diode has two silver bands around it. It doesn't look overheated.
The area near this diode has a magnetron coupled with 2 wires to a trafo and one to a capacitor which continues through the diode to ground. A third wire on the trafo goes to the second terminal of the capacitor.
If I could have this diode identified , I'd greatly appreciate it.
and inscribe 721.63252301 into the search box. It should point to exploded view diagrams with part numbers.
The diode is rather generic and commonly available:
12Kv 350ma
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Replace the cap, diode and mag. Tear the cover off and inspect the waveguide, stirrer and outlet covering for arcing. Check the interior for arcing. Watch the cap it can bite you. Have a micro detector and check for leaking door and overall leaks.
Or just buy a new oven.
Best for the buck in my opinion is the GE 1100 watt or Sharp.
You might wanna look into a diode with better ratings. I see 15Kv
500ma diodes available in the same form factor.
As Mr Meat Plow mumbled, check for arcing. The snapping noise you heard may have been arcing in the waveguide or maggot-tron. You can usually see some evidence of the burn like damage on the waveguide walls. If you have it apart, it's easy to inspect (with a dental mirror). I must be leading a charmed life, but I've only seen arcing twice. Both were caused by a bad fit between the waveguide and the maggot-tron causing high VSWR and thus high voltages. You might want to check if everything is assembled correctly and fits tight.
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# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS
Such "safety" issues are for people that don't understand how things work. Increasing the voltage and current rations on the damping diode
25% might give a the OP a bit more voltage margin if he's doing something that might cause arcing. However, it's not going to prevent blowing the breaker or the diode with a very high VSWR situation caused by an arc simulating a sorted waveguide, which reflects all the forward power back to the maggot-tron. For infinite VSWR, the maggot-tron is going to see about twice the normal operating voltage (if the reflected signal is in phase) or twice the current draw (if the reflected signal is otto phase). Both those situation will blow the diode from either too much voltage or too much current.
My assumption (possibly incorrect) is that commodity consumer products are usually designed with minimim component specs and margin to save costs. Under normal operating conditions, it wouldn't matter if it were a 12kV/350ma or 15kV/500ma diode but the lower rating is probably a few pennies cheaper. If it's a bad fit between around the waveguide causing internal arcing, then it won't matter which one is used. Either both blow. If it's something else, it might offer slightly more time before blowing to determine the cause.
Full disclosure: I vaguely recall repairing (i.e. replaced parts inside) about 5 assorted microwave ovens. It's not what I normally do. I will concede that I'm not that experienced in mw oven repair. One point for you.
Thanks. I perform an un-natural act by agreeing with your comment and you still shovel the manure. What does it take to obtain your approval?
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Do a test on the diode, then; it's unlikely that it is dead, but possible. A 'pop' can mean any kind of spark, a smell can be left over from the first failure, and 'loud hum' might mean you hear the fan motor loudly when you listen (but would ignore it in normal circumstances).
Most microwave oven failures are traced to the interlock switches and fuses, so check those too.
All tests will be with the power disconnected, and the capacitor discharged (i.e. crowbar it with an insulated handle tool), of course.
I did factory repair for cheap brands like but not limited to Goldstar and Tatung (basically Korean) back when the Amana Radar Range models started to be taken over by those who didn't have a grand to spend on the cheapest Amana. Also have worked on a ton of commercial Amanas (every Burger King seemed to have at least one back then.)
On another note, stop with the cheap shot innuendoes. It's hard to respect those even with the vast knowledge you have when they f*ck with you in a non humorous manner.
Ok, you're an experienced expert, assuming you didn't just juggle sub-assemblies and modules. However, I still think that increasing the diode rating 25% is a good idea and doesn't have an effect on safety, unless the diode is somehow used as a crowbar to blow the fuse.
I'm not sure I know how to do that without being abusive, abrasive, irritating, obnoxious, humiliating, etc. I've been answering usenet questions for so long, that it's become almost an institution. It's also fun. Of course, when customers pay for my advice, I can be diplomatic. On rare occasions, I even use a spelling chequer.
It might be helpful if I point out that few of my assorted usenet rants are intended to be insulting. They're intended to inspire the intended target to think. I never offer an opinion without substantiation, usually in detail, and with plenty of examples, URL's, analogies, and detail. I've experimented with various styles of answering questions and engaging in discussions. Humor, mixed with satire, and a dash of "you're not meeting my expectations" is what seems to work best for me. Motivation through humiliation is not very popular or politically correct, but it works well. For example, getting people with questions to supply enough information to answer their question is often a difficult process. If you are on the receiving end of one of my detailed rants, you might ask yourself why I would spend the time on you.
Re-reading my previous rants in this thread, I don't see where I have "f*ck(ed) with you in a non-humorous manner". If I did, it was not intentional, so please accept my apologies. However, if you're complaining about my style or method of argumentation, as I indicated, I'm not sure I can change that even if I wanted to do so.
However, I'll offer you a deal. I'll try to control my verbal fencing with you, if you will ease up on the profanity (even when I screwup). I don't have a problem with profanity, except that it creates a generally unprofessional impression. I just hate to see someone do that to themselves.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
My thanks to everyone for their interest and efforts and my condolences for the strains.
To answer a question from just above, there is no doubt that the hum that appeared just before I shut the oven off was FAR louder than the normal operating level.
The situation now is that the replacement diode I ordered has arrived and is now installed. Question now is, should I start up the oven or getter a stronger diode? Thanks Jeff for the suggestion.
I looked through the Sears website (Thanks Jeff) and found the model but the transformer, magnetron and diode are missing. Even a search for the word diode gives nothing.
BTW, has anyone seen the wierd screws that are used to keep the cover on the oven? They are Torx but with a difference. There is a tiny but very strong spike right in the middle of the hole in the screw where the key fits. SO in essence, to remove the screws the right way, a Torx key with a hole in it is the way to go. That should keep most users away but not engineers, mechanics and other knowledgeable folks :-)
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
25% "better" will probably also blow up.
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.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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.
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W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
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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.
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Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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