inc@tc.fluke.COM (Gary Benson) (09/08/89)
Last night my 4-year old Tappan microwave oven chattered, buzzed, and died in the middle of baking some potatoes. Removing it from the counter, I heard some rattling noises inside, so down on the floor, I kind of jiggled it, and confirmed that yup, something was in there. Continued jiggling resulted in half a rather large diode dropping out onto the rug. I was all ready to take it into the shop until a visibly defective part fell into my hands. My experience with all kinds of repair shops is they charge what the traffic will bear, regardless of the problem's difficulty or being presented with a solid troubleshooting clue like half a diode. Now I'm a safety-conscious kind of guy, and so I always heed those little warnings on the back of things I've never worked on. In other words, I usually ignore them, figuring my electonics background, 5 years repairing stereos, and inate carefulness probably qualify me more than your average appliance repair person, but something about opening up a microwave oven has me a little spooked. Does anyone out there have experience in repairing microwave ovens? If I open this unit up, what are the chances I am going to destroy the dimensions of a precisely formed cavity's geometries and wind up with a microwave canon to the gonads instead of an oven? Are there any special seals or safety interlocks to look out for and replace? Once inside, I should be able to find my way around the circuit ok, and if I go in, I would also want to check the klystron. But I figure the tube checker down at Radio Shack probably won't have the right pinout ;-), so do you have any ideas on how to check the tube? Take it into the local appliance repair guy? Thanks for any insight you can provide! -- Gary Benson inc@tc.fluke.COM John Fluke MfgCoInc, Everett WA -- GaryBenson_-inc@tc.fluke.COM-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_ -_-_-_-_-_-_-_-_-_-_-_-_-_-_-Tell the girls to slice the ham thin -J.C. Penney
kencr@haddock.ima.isc.com (Kenny Crudup) (09/09/89)
In article <10931@fluke.COM> inc@tc.fluke.COM (Gary Benson) says: >Last night my 4-year old Tappan microwave oven chattered, buzzed, and died >in the middle of baking some potatoes. >Continued jiggling resulted in half a rather large diode dropping out onto >the rug. >Does anyone out there have experience in repairing microwave ovens? Yup. I used to fix 'em in a stereo place back where I went to school. >If I open this unit up, what are the chances I am going to destroy the >dimensions of a precisely formed cavity's geometries and wind up with a >microwave cannon to the gonads instead of an oven? Real small. The magnetron is coupled to the resonating area, and the whole shebang is fastened to the 'oven' part. Most electrics are accessible without messing with any of that. But- DON'T TOUCH THE FLUX CAPACITOR!! :-) >Are there any special seals or safety interlocks to look out for and replace? All the ones I worked on had nothing but an AC cutout on the back panel. No seals, and all the i-locks are obvious (more AC cutouts). However- make sure the geometric association reference modulated oscillator threshold point is less than the residual charge current! (OK, OK, more bullshit, sorry :-) >Once inside, I should be able to find my way around the circuit ok, and if >I go in, I would also want to check the klystron. Yeah. I would wonder if the dead diode is the cause or the effect. >So do you have any ideas on how to check the tube? Take it into the local >appliance repair guy? >Gary Benson inc@tc.fluke.COM I doubt they would do more than change it. Provided the mag is really the cause, you can always 'smoke-test' the diode.... But anyway, these things are, for the most part, meant to be fixed by your average appliance hack, so they are relatively idiot-proof, if you know your way around a high-voltage circuit. -- Kenneth R. Crudup, Contractor, Interactive Systems Co.(386/ix), Cambridge MA Phone (617) 661 7474 x238 Bensonhurst, NYC - Howard Beach '89. Kinder, gentler huh? Right!! {encore, harvard, spdcc, think}!ima!haddock!kencr kencr@ima.ima.isc.com
inc@tc.fluke.COM (Gary Benson) (09/10/89)
Thanks to all of you who e-mailed and posted replies to my call for help with my microwave oven. Based on your reassurances that the magnetron-waveguide-cavity system is separate and well-sealed from the electronics parts, I confidentlyu opened the thing up. Glad I did, too. It was educational and fun to finally seen the parts I had so long imagined. My wife's comment was that it looked simpler than she had imagined it would. Apparently the diode was the only part that fried, and a couple of people indicated that what I had was a typical failure mode. But the replacement charge was obscene: 19.95 + tax!! sheesh! One guy told me it is about a 1 amp 6 kV PIV part, so if I ever have a need to fix this beast again, I'll look for "non-authorized" replacement parts! Through all this, I also located the original sales receipt and owners manual, and learned that the magnetron carries a *10 YEAR* guarantee. Does anyone know why they offer such a thing? Don't magnetrons break or something? -- GaryBenson_-inc@tc.fluke.COM-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_ -_-_-_-_-_-_-_-_-_-_-_-_-_-_-Tell the girls to slice the ham thin -J.C. Penney
mmm@cup.portal.com (Mark Robert Thorson) (09/11/89)
> shebang is fastened to the 'oven' part. Most electrics are accessible without > messing with any of that. But- DON'T TOUCH THE FLUX CAPACITOR!! :-) I'll say. I touched one of those, and now my right index finger is permanently magnetized. I had no idea a capacitor could store so much magnetic energy.
johne@hpvcfs1.HP.COM (John Eaton) (09/12/89)
<<<< > shebang is fastened to the 'oven' part. Most electrics are accessible without > messing with any of that. But- DON'T TOUCH THE FLUX CAPACITOR!! :-) ---------- The Flux Cap is the most important part of a microwave. Most people think that a microwave simply cooks food faster. This is of course false since many people will watch a microwave while it cooks and we all know the theory about a watched pot. A microwave cooks food very slowly and then sends it back in time to a point a few minutes after you put it in. This is why you should never leave food in a microwave to long. If you do it will get sent back TWICE and begin compounding. The result will be an explosion of whatever you were cooking. You can easily test the time transfer ability of your microwave by placing your wristwatch in it and setting it to INCINERATE. Remove it one hour later and you will notice that your watch no longer has the correct time. John Eaton !hpvcfs1!johne
ISW@cup.portal.com (Isaac S Wingfield) (09/12/89)
Gary Benson writes:
------------------------------
Through all this, I also located the original sales receipt and owners
manual, and learned that the magnetron carries a *10 YEAR* guarantee. Does
anyone know why they offer such a thing? Don't magnetrons break or something?
------------------------------
Our ~20 year old Sears is still going strong, though the timer broke
about 12 years ago. Sears wanted $90 for a new one, so we just turn
it on and keep an eye on what's in it.
Magnetrons are structurally very simple (though technically complex)
beasties, and are quite robust. They do contain a *large* magnet, so
don't store your floppies on top of your microwave.
Isaac
isw@cup.portal.compcf@galadriel.bt.co.uk (Pete French) (09/14/89)
From article <1430007@hpvcfs1.HP.COM>, by johne@hpvcfs1.HP.COM (John Eaton): > a microwave to long. If you do it will get sent back TWICE and begin compounding. > The result will be an explosion of whatever you were cooking. You can easily Actually food can explode in a uWave. I knew somebody who was doing a haggis for a dinner party - after 5 hourss itr was sitting in the saucepan in some horrible fatty water not looking very cooked so she decided to give it a quick turn in the old uWave. In it went and started cooking - about 1 minute later it suddenly shrunk to the size of a tennis ball (quite impressivce for a haggis) and then violently exploded leaving haggis entrails all over the uWave. Tjis sounds more like the behaviour of a neutron star than an object of food. Anbody cot any ideas as to why it conracted before exploding ? -Pete. -- -Pete French. | British Telecom Research Labs. | "The carefree days are distant now, Martlesham Heath, East Anglia. | I wear my memories like a shroud..." All my own thoughts (of course) | -SIOUXSIE
ingoldsb@ctycal.COM (Terry Ingoldsby) (09/15/89)
In article <10931@fluke.COM>, inc@tc.fluke.COM (Gary Benson) writes: > Last night my 4-year old Tappan microwave oven chattered, buzzed, and died > in the middle of baking some potatoes. Removing it from the counter, I heard > some rattling noises inside, so down on the floor, I kind of jiggled it, and > confirmed that yup, something was in there. Continued jiggling resulted in > half a rather large diode dropping out onto the rug. It sounds like the stack diode is gone (stack diode = a bunch of diodes in series to give a very high voltage rating). You should be able to solder a new one in place without disturbing any of the microwave producing components. I believe there is a SAMS book on microwave repair you might want to consult. -- Terry Ingoldsby ctycal!ingoldsb@calgary.UUCP Land Information Systems or The City of Calgary ...{alberta,ubc-cs,utai}!calgary!ctycal!ingoldsb
ingoldsb@ctycal.COM (Terry Ingoldsby) (09/15/89)
In article <10979@fluke.COM>, inc@tc.fluke.COM (Gary Benson) writes: > Apparently the diode was the only part that fried, and a couple of people > indicated that what I had was a typical failure mode. But the replacement > charge was obscene: 19.95 + tax!! sheesh! One guy told me it is about a > 1 amp 6 kV PIV part, so if I ever have a need to fix this beast again, I'll > look for "non-authorized" replacement parts! Every microwave oven problem I've ever encountered involved either the stack diode going bad, or occasionally the mixer (a little fan blade affair that rotates above the cavity) getting stuck. The stack diode is subjected to very high voltage, and they do tend to deteriorate. Since they are essentially a series string of diodes, when one diode goes bad (shorts) the others bear more and more of the burden until it finally goes south. > > Through all this, I also located the original sales receipt and owners > manual, and learned that the magnetron carries a *10 YEAR* guarantee. Does > anyone know why they offer such a thing? Don't magnetrons break or something? > There is not much inside a magnetron. I've never heard of one going bad but I will ask a friend who works in a repair shop. -- Terry Ingoldsby ctycal!ingoldsb@calgary.UUCP Land Information Systems or The City of Calgary ...{alberta,ubc-cs,utai}!calgary!ctycal!ingoldsb
kencr@haddock.ima.isc.com (Kenny Crudup) (09/15/89)
In article <348@galadriel.bt.co.uk> pcf@galadriel.bt.co.uk (Pete French) says: >It.... >shrunk to the size of a tennis ball (quite impressivce for a haggis) and then >violently exploded leaving haggis entrails all over the uWave. ------ -------- Isn't this redundant? :-) -- Kenneth R. Crudup, Contractor, Interactive Systems Co.(386/ix), Cambridge MA Not all men are fools; some are still single! Phone (617) 661 7474 x238 {encore, harvard, spdcc, think}!ima!haddock!kencr kencr@ima.ima.isc.com
john@frog.UUCP (John Woods) (09/17/89)
In article <461@ctycal.UUCP>, ingoldsb@ctycal.COM (Terry Ingoldsby) writes: > In article <10979@fluke.COM>, inc@tc.fluke.COM (Gary Benson) writes: > > Apparently the diode was the only part that fried... > > 19.95 + tax!! sheesh! One guy told me it is about a 1 amp 6 kV PIV part, > Every microwave oven problem I've ever encountered involved either the > stack diode going bad, or occasionally the mixer (a little fan blade > affair that rotates above the cavity) getting stuck. Check out a recent ARRL Handbook for info about high voltage diodes (and for some suppliers; "K2AW's Silicon Alley" is fairly well known). > > the magnetron carries a *10 YEAR* guarantee. > There is not much inside a magnetron. I've never heard of one going bad but > I will ask a friend who works in a repair shop. You have now: I had the magnetron in my microwave go bad after 3 MONTHS. The filament crapped out. The replacement has been going strong for a year since, and will likely continue to do so. But it does happen. -- John Woods, Charles River Data Systems, Framingham MA 508-626-1101 ...!decvax!frog!john, john@frog.UUCP, ...!mit-eddie!jfw, jfw@eddie.mit.edu
fjs@floyd.ATT.COM (Fred Shubert ,2A-154,3094,ATTBL) (09/20/89)
In article <460@ctycal.UUCP>, ingoldsb@ctycal.COM (Terry Ingoldsby) writes: > In article <10931@fluke.COM>, inc@tc.fluke.COM (Gary Benson) writes: > > Last night my 4-year old Tappan microwave oven chattered, buzzed, and died > > in the middle of baking some potatoes. Removing it from the counter, I heard I got a 2 year old Sharp Carousel II Nuker and unfortunately one night I had the same problem, but not with taters :-) Anyhoo, the mild stench of burning wire insulation prompted me to remove the oven cover. Lo and behold, the secondary on the xformer was toasted (black scortch mark, lots of carbon, and bubbled metal). More than likely happened because the nuker has been in a sorta-closed area (improper ventilation). My questions: 1) I know that the tube is isolated via the xformer, but how can I check it (resistance measurement??) just to be sure no damage occurred??????? 2) My nuker has one large diode/resistor assembly (packaged-sealed) that is connected between gnd and the .8uF bypass cap (LARGE!!). Its resistance is approx. 15M ohms. Does this sound right?? I'm picking up a new xformer tonight and will try it. My hopes are not of the highest altitude, so hopefully someone has some suggestions for me to read come the morning. Cost for the xformer: $60.00 If I gotta get a tube, I might as well build a nuker!! (How much do tubes cost??) Much thanks. Fred J. Shubert | "You haven't lived until you've seen a 'cat fly!!!" AT&T Bell Labs |----------------------------------------------------- Whippany, N.J. | DISCLAIMER: All views are that of my own. PERIOD. Ma-Bell 201-386-3094 | Who else could be so 'cat crazy!! | _ | | /^ ^\ | F-14D ____________|_( . )_|____________ SUPERTOMCATS --*/--|_| (___) |_|--\*-- RULE * O O * (I Love 'Em) Let's turn and burn!!