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Weird Microwave problem - trips breaker when you shut the door!
We are finsihing up a new construction home, and have a Viking
Microwave on a 20 amp circuit in the kitchen. This is the only device on the circuit. The microwave cooks fine, but sometimes just closing the door on the microwave trips the breaker! I have moved the oven to another outlet and it doesn't trip other breakers. ANy ideas what might be happeing? I can't imagine closing the door would draw a lot of current! We have used other devices on the same outlet with no problems. thanks! To reply via email remove spamnot |
Spudz wrote: We are finsihing up a new construction home, and have a Viking Microwave on a 20 amp circuit in the kitchen. This is the only device on the circuit. The microwave cooks fine, but sometimes just closing the door on the microwave trips the breaker! I have moved the oven to another outlet and it doesn't trip other breakers. ANy ideas what might be happeing? I can't imagine closing the door would draw a lot of current! We have used other devices on the same outlet with no problems. thanks! To reply via email remove spamnot is it a GFI breaker? there is probably an intermittent short in the oven i.e. a wire with cut insulation or something Mark |
Spudz, sounds like the door is misaligned. When the door is misaligned,
the interlocks switches in the holes where the "hooks" on the door go don't activate in the right sequence and the circuits breaker trips or the microwave's internal fuse blows. This, surprisingly, is actually a feature. It is existant to prevent you from operating it with a damaged or misaligned door so you don't expose yourself to potentially harmful levels of microwaves. Have the door check and, if needed, realigned professionally. Unless you have the skills and tools to test for uWave leaks (which I highly doubt), don't fix it yourself. The repair FAQ website has info on the interlocks and about microwave doors if you DO want to try to fix it. The URL for the Repair FAQ on microwaves is: http://repairfaq.ece.drexel.edu/sam/micfaq.htm |
Spudz, sounds like the door is misaligned. When the door is misaligned,
the interlocks switches in the holes where the "hooks" on the door go don't activate in the right sequence and the circuits breaker trips or the microwave's internal fuse blows. I have seen this happen. This, surprisingly, is actually a feature. It is existant to prevent you from operating it with a damaged or misaligned door so you don't expose yourself to potentially harmful levels of microwaves. Have the door check and, if needed, realigned professionally. Unless you have the skills and tools to test for uWave leaks (which I highly doubt), don't fix it yourself. The repair FAQ website has info on the interlocks and about microwave doors if you DO want to try to fix it. The URL for the Repair FAQ on microwaves is: http://repairfaq.ece.drexel.ed=ADu/sam/micfaq.htm |
Well that's interesting - so if the door is misaligned, the oven
shorts the AC line to ground and forces the circuit breaker to blow? That's bizarre! Spudz On 28 Jun 2005 12:39:08 -0700, "nvic" wrote: Spudz, sounds like the door is misaligned. When the door is misaligned, the interlocks switches in the holes where the "hooks" on the door go don't activate in the right sequence and the circuits breaker trips or the microwave's internal fuse blows. I have seen this happen. This, surprisingly, is actually a feature. It is existant to prevent you from operating it with a damaged or misaligned door so you don't expose yourself to potentially harmful levels of microwaves. Have the door check and, if needed, realigned professionally. Unless you have the skills and tools to test for uWave leaks (which I highly doubt), don't fix it yourself. The repair FAQ website has info on the interlocks and about microwave doors if you DO want to try to fix it. The URL for the Repair FAQ on microwaves is: http://repairfaq.ece.drexel.ed*u/sam/micfaq.htm To reply via email remove spamnot |
Spudz wrote:
Well that's interesting - so if the door is misaligned, the oven shorts the AC line to ground and forces the circuit breaker to blow? That's bizarre! Spudz Via a low ohm high wattage resistor, it doesn`t just short out the mains with an almighty Kerbanggg! Ron -- Lune Valley Audio Public address system Hire, Sales, Repairs www.lunevalleyaudio.com |
Okay well I'll have the unit checked - years of buying cheap
microwaves, never had a problem - we buy a high-end unit and the thing is having problems right out of the box. Go figure. THanks, spudz On Tue, 28 Jun 2005 20:02:13 +0000 (UTC), "Ron(UK)" wrote: Spudz wrote: Well that's interesting - so if the door is misaligned, the oven shorts the AC line to ground and forces the circuit breaker to blow? That's bizarre! Spudz Via a low ohm high wattage resistor, it doesn`t just short out the mains with an almighty Kerbanggg! Ron To reply via email remove spamnot |
"Ron(UK)" writes:
Spudz wrote: Well that's interesting - so if the door is misaligned, the oven shorts the AC line to ground and forces the circuit breaker to blow? That's bizarre! Spudz Via a low ohm high wattage resistor, it doesn`t just short out the mains with an almighty Kerbanggg! Actually, it does. Because, that situation should never occur unless there is a major problem. --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
odd that it is tripping the 20A breaker before it blows the 15A
internal fuse though, unless the internal fuse is 20 A. I have also seen bad breakers before, tripping at a lower rating than they are supposed to be, but they have all been old. But if the microwave is not tripping on other outlets, this may be something you want to look into |
"darren" wrote in message ... odd that it is tripping the 20A breaker before it blows the 15A internal fuse though, unless the internal fuse is 20 A. I have also seen bad breakers before, tripping at a lower rating than they are supposed to be, but they have all been old. But if the microwave is not tripping on other outlets, this may be something you want to look into If you plotted current vs. time for the fuse, the breaker and the microwave you'd probably figure it out but at this point .... N |
to ron: The one i took apart with same problem and dying mag did.
switch across main, hot to neutral. see Sam GoldWasser's post. |
"Spudz" bravely wrote to "All" (28 Jun 05 11:37:05)
--- on the heady topic of "Weird Microwave problem - trips breaker when you shut the door!" Sp From: Spudz Sp Xref: aeinews sci.electronics.repair:51789 Sp We are finsihing up a new construction home, and have a Viking Sp Microwave on a 20 amp circuit in the kitchen. This is the only device Sp on the circuit. The microwave cooks fine, but sometimes just closing Sp the door on the microwave trips the breaker! I have moved the oven to Sp another outlet and it doesn't trip other breakers. ANy ideas what Sp might be happeing? I can't imagine closing the door would draw a lot Sp of current! We have used other devices on the same outlet with no Sp problems. Sp thanks! I saw this very thing last year. Turned out one of the contacts on the electric meter was burning up. Your problem is not likely to be the same but coincidences happen. Perhaps instead the microwave has a door interlock problem. These are designed to trip the breaker, for safety. Is it pretty new? A*s*i*m*o*v .... On an electrician's truck: Let Us Remove Your Shorts |
"Ron(UK)" wrote in message ... Spudz wrote: Well that's interesting - so if the door is misaligned, the oven shorts the AC line to ground and forces the circuit breaker to blow? That's bizarre! Spudz Via a low ohm high wattage resistor, it doesn`t just short out the mains with an almighty Kerbanggg! It does on the microwaves I've worked on, the secondary interlock switch shorts directly across the line and blows the fuse, of course this is never supposed to happen in actual operation, but is a last resort to prevent exposure to high power microwave energy should the primary interlock stick. |
nvic wrote:
to ron: The one i took apart with same problem and dying mag did. switch across main, hot to neutral. see Sam GoldWasser's post. That must be the US way then, in over 15 years of repairing microwave ovens* here in the UK I can't recall seeing one without the resistor.(Sometimes it looks like a slowblow fuse, with what looks like a spring inside) It should still blow the internal fuse first unless the mains breaker is unusually sensitive * A business now sadly gone, people just buy a cheap replacement, it`s cheaper to buy a new oven than to have a fuse replaced Ron -- Lune Valley Audio Public address system Hire, Sales, Repairs www.lunevalleyaudio.com |
"Spudz" wrote in message ... We are finsihing up a new construction home, and have a Viking Microwave on a 20 amp circuit in the kitchen. This is the only device on the circuit. The microwave cooks fine, but sometimes just closing the door on the microwave trips the breaker! I have moved the oven to another outlet and it doesn't trip other breakers. ANy ideas what might be happeing? I can't imagine closing the door would draw a lot of current! We have used other devices on the same outlet with no problems. thanks! To reply via email remove spamnot A couple of additional possibilities. Note that some circuit breakers will pop before a slo-blo fuse in the same line. Think door switches and read on. Food material can gather at the operating pip of any of the door micro switches. This can be as small as a very light smear of something sticky. The effect is to slow down the operating speed of one or more switches. This will cause an intermittent door switch timing overlap when either opening or closing the door. The actual switch sequence, the switch affected by food debris, and the particular design of the oven will cause a variety of different scenarios. THIS IS A COMMON FAULT. You may need a 10X jewellers loupe to see some food smears which are fully capable of causing a switch to hang long enough to blow a fuse or trip a breaker. Another fairly common cause for a switch to hang and disrupt the interlock sequence is much harder to detect and has a greater capacity to have you re-working ovens at your expense. This primarily affects the switch in the sequence that acts as the crowbar, but can also affect even clean primary/secondary switches after some years use. If an oven has had a history of one or more fuses blown without a fault being discovered, the crowbar switch will have had some serious energy fed into its shorted contacts. This ALWAYS leaves a roughened area on the contacts. Roughened contacts do not slide as easily as pristine ones and the slowed-down switch is now likely to blow a fuse intermittently, ***even if the cause for the original fault is found and corrected.*** Best practise, is to ALWAYS, if possible, examine with a loupe the contact area of crowbar door switches. Trust no door switches that have switched full current through them to blow the main fuse. If you have a customer oven or two that blow switches every week or so, suspect food debris and/or roughened contacts. In my experience, most door switch problems with microwave ovens are caused by (sometimes) tiny amounts of food. I used to buy, and use, 5000 microswitches every 6 weeks or so for this very reason. You cannot effectively clean food debris off switches. Always put new switches into clean housings. To do otherwise is to risk doing the job again ***at your expense*** |
Yes its brand new - we just took it back to the dealer yesterday and
they said they can fix/adjust it. We moved the ven to another outlet (20 A) and it did the same thing... eventually it must have blown the internal fuse in the oven cuz now it won;t even power up any more. Thanks again for the advice... I wll never look at a microwave oven door the same again! :) On Tuesday, 28 Jun 2005 23:03:00 -500, "Asimov" wrote: "Spudz" bravely wrote to "All" (28 Jun 05 11:37:05) --- on the heady topic of "Weird Microwave problem - trips breaker when you shut the door!" Sp From: Spudz Sp Xref: aeinews sci.electronics.repair:51789 Sp We are finsihing up a new construction home, and have a Viking Sp Microwave on a 20 amp circuit in the kitchen. This is the only device Sp on the circuit. The microwave cooks fine, but sometimes just closing Sp the door on the microwave trips the breaker! I have moved the oven to Sp another outlet and it doesn't trip other breakers. ANy ideas what Sp might be happeing? I can't imagine closing the door would draw a lot Sp of current! We have used other devices on the same outlet with no Sp problems. Sp thanks! I saw this very thing last year. Turned out one of the contacts on the electric meter was burning up. Your problem is not likely to be the same but coincidences happen. Perhaps instead the microwave has a door interlock problem. These are designed to trip the breaker, for safety. Is it pretty new? A*s*i*m*o*v ... On an electrician's truck: Let Us Remove Your Shorts |
Spudz wrote:
We are finsihing up a new construction home, and have a Viking Microwave on a 20 amp circuit in the kitchen. This is the only device on the circuit. The microwave cooks fine, but sometimes just closing the door on the microwave trips the breaker! I have moved the oven to another outlet and it doesn't trip other breakers. ANy ideas what might be happeing? I can't imagine closing the door would draw a lot of current! We have used other devices on the same outlet with no problems. thanks! To reply via email remove spamnot When the door closes there are multiple interlocks. These are set up to short the ac line and blow the internal fuse if you try to defeat just one interlock. If there were a brief transient short when you close the door it could trip a magnetic breaker before blowing the internal fuse. The fact that it is a problem on one circuit and not another may have to do with the senitivity of the braker which may vary from breaker to breaker. If you are qualified to do work in your breaker box (DO NOT IF YOU AREN"T SURE WHAT YOU ARE DOING!!) you might simply swap the breaker from the circuit that works to the circuit that's sensitive. Or, you could get an electrician to do it. That's the only way I can see a connection with closing the microwave door unless there is faulting wiring in the outlet that is jarred when you close the door. If that is the case you could possibley get the same effect thumping on the countertop or wall. Good luck. Jim |
Why not jsut plug the uWave into another circuit and unplug everything
else on the circuit. if it trips, it can't be a over-sensitive breaker. |
James Sweet wrote:
It does on the microwaves I've worked on, the secondary interlock switch shorts directly across the line and blows the fuse, of course this is never supposed to happen in actual operation, but is a last resort to prevent exposure to high power microwave energy should the primary interlock stick. Since virtually all microwaves now seem to be run by electronics, I wonder why they don't just program the CPU to detect interlock failures and go into an error condition and refuse to operate, instead of shorting the AC line? That would sound a lot safer to me. Then again, I'm not an expert, so maybe I'm missing something. -- Travis Evans [The email address on this post is valid, but may change from time to time. Make sure you use the latest email address; if you use an old one, I will not receive your message.] |
"Travis Evans" wrote in message news:6MYwe.6412$Eo.1948@fed1read04... Since virtually all microwaves now seem to be run by electronics, I wonder why they don't just program the CPU to detect interlock failures and go into an error condition and refuse to operate, instead of shorting the AC line? That would sound a lot safer to me. Then again, I'm not an expert, so maybe I'm missing something. What if the main control (triac, relay) which feeds the magnetron shorts out? N |
Travis Evans writes:
James Sweet wrote: It does on the microwaves I've worked on, the secondary interlock switch shorts directly across the line and blows the fuse, of course this is never supposed to happen in actual operation, but is a last resort to prevent exposure to high power microwave energy should the primary interlock stick. Since virtually all microwaves now seem to be run by electronics, I wonder why they don't just program the CPU to detect interlock failures and go into an error condition and refuse to operate, instead of shorting the AC line? That would sound a lot safer to me. Then again, I'm not an expert, so maybe I'm missing something. Have you ever heard of software screwing up? Nah. :) That arrangement of 3 interlock switches is much more fail-safe than anything depending on 0s and 1s. --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
"Sam Goldwasser" wrote in message ... Have you ever heard of software screwing up? Nah. :) That arrangement of 3 interlock switches is much more fail-safe than anything depending on 0s and 1s. A Canadian company made a programmable radiation treatment machine. If you entered the wrong setting, then backspaced and corrected it, the patient got the maximum the machine could deliver. Killed some people before they found the bug. N |
"NSM" writes:
"Sam Goldwasser" wrote in message ... Have you ever heard of software screwing up? Nah. :) That arrangement of 3 interlock switches is much more fail-safe than anything depending on 0s and 1s. A Canadian company made a programmable radiation treatment machine. If you entered the wrong setting, then backspaced and corrected it, the patient got the maximum the machine could deliver. Killed some people before they found the bug. Yes, that was a classic. I always love how some people think software can take care of everything. There are some cases where a simple switch is far more reliable. --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
"Travis Evans" wrote in message news:6MYwe.6412$Eo.1948@fed1read04... James Sweet wrote: It does on the microwaves I've worked on, the secondary interlock switch shorts directly across the line and blows the fuse, of course this is never supposed to happen in actual operation, but is a last resort to prevent exposure to high power microwave energy should the primary interlock stick. Since virtually all microwaves now seem to be run by electronics, I wonder why they don't just program the CPU to detect interlock failures and go into an error condition and refuse to operate, instead of shorting the AC line? That would sound a lot safer to me. Then again, I'm not an expert, so maybe I'm missing something. When electronic control boards were still on only half of the microwave ovens sold, it was a common-place to suggest to customers on the phone that if they were to unplug the oven from the wall outlet for a minute or two, the (software) fault they were describing would probably correct itself. Many times it did! |
"JustMe" á@á wrote in message u... When electronic control boards were still on only half of the microwave ovens sold, it was a common-place to suggest to customers on the phone that if they were to unplug the oven from the wall outlet for a minute or two, the (software) fault they were describing would probably correct itself. Many times it did! When ovens all had mechanical timers I got many a panic call from someone who couldn't figure out why their oven had stopped working but the hotplates were fine. I got quite skilled at leading them through the reset procedure over the phone - saved a drive. N |
"Travis Evans" wrote in message news:6MYwe.6412$Eo.1948@fed1read04... James Sweet wrote: It does on the microwaves I've worked on, the secondary interlock switch shorts directly across the line and blows the fuse, of course this is never supposed to happen in actual operation, but is a last resort to prevent exposure to high power microwave energy should the primary interlock stick. Since virtually all microwaves now seem to be run by electronics, I wonder why they don't just program the CPU to detect interlock failures and go into an error condition and refuse to operate, instead of shorting the AC line? That would sound a lot safer to me. Then again, I'm not an expert, so maybe I'm missing something. Then you're relying on all the electronics to be functional as well as the software to be bug free, in real life there's just way too many chances for that to not work. They've been doing it the way they do for 30 years now and I've not heard of a single safety issue coming up in relation to that. |
"James Sweet" bravely wrote to "All" (01 Jul 05 06:30:35)
--- on the heady topic of " Weird Microwave problem - trips breaker when you shut the door!" JS From: "James Sweet" JS Xref: aeinews sci.electronics.repair:52068 JS "Travis Evans" wrote in message JS news:6MYwe.6412$Eo.1948@fed1read04... Since virtually all microwaves now seem to be run by electronics, I wonder why they don't just program the CPU to detect interlock failures and go into an error condition and refuse to operate, instead of shorting the AC line? That would sound a lot safer to me. Then again, I'm not an expert, so maybe I'm missing something. JS Then you're relying on all the electronics to be functional as well as JS the software to be bug free, in real life there's just way too many JS chances for that to not work. They've been doing it the way they do for JS 30 years now and I've not heard of a single safety issue coming up in JS relation to that. Software isn't as unreliable as you infer since there are planes which operate "fly by wire" over our heads at this very instant. Hundreds of millions of passengers per year are trusting their lives to a line of code translated to 1's and 0's. These FBW planes even use joysticks! Like it or not, the world is now a giant video game... PONG rulz! A*s*i*m*o*v .... Digital circuits are made from analog parts. |
"Asimov" writes:
"James Sweet" bravely wrote to "All" (01 Jul 05 06:30:35) --- on the heady topic of " Weird Microwave problem - trips breaker when you shut the door!" JS From: "James Sweet" JS Xref: aeinews sci.electronics.repair:52068 JS "Travis Evans" wrote in message JS news:6MYwe.6412$Eo.1948@fed1read04... Since virtually all microwaves now seem to be run by electronics, I wonder why they don't just program the CPU to detect interlock failures and go into an error condition and refuse to operate, instead of shorting the AC line? That would sound a lot safer to me. Then again, I'm not an expert, so maybe I'm missing something. JS Then you're relying on all the electronics to be functional as well as JS the software to be bug free, in real life there's just way too many JS chances for that to not work. They've been doing it the way they do for JS 30 years now and I've not heard of a single safety issue coming up in JS relation to that. Software isn't as unreliable as you infer since there are planes which operate "fly by wire" over our heads at this very instant. Hundreds of millions of passengers per year are trusting their lives to a line of code translated to 1's and 0's. These FBW planes even use joysticks! Like it or not, the world is now a giant video game... PONG rulz! OK, next time I want to spend $20,000,000 for a microwave oven I'll keep that in mind. :) --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
"Asimov" wrote in message ... Software isn't as unreliable as you infer since there are planes which operate "fly by wire" over our heads at this very instant. Hundreds of millions of passengers per year are trusting their lives to a line of code translated to 1's and 0's. These FBW planes even use joysticks! Like it or not, the world is now a giant video game... PONG rulz! Some ground worker duct taped over the instrument holes on a plane and killed everyone on board. N |
Software isn't as unreliable as you infer since there are planes which operate "fly by wire" over our heads at this very instant. Hundreds of millions of passengers per year are trusting their lives to a line of code translated to 1's and 0's. These FBW planes even use joysticks! Like it or not, the world is now a giant video game... PONG rulz! The process of designing, writing and most importantly, testing the software used in an aircraft are completely different from that for the firmware in a microwave oven. There's just no comparison. |
"Sam Goldwasser" bravely wrote to "All" (01 Jul 05 14:35:24)
--- on the heady topic of " Weird Microwave problem - trips breaker when you = shut the door!" SG From: Sam Goldwasser SG Xref: aeinews sci.electronics.repair:52109 SG "Asimov" writes: "James Sweet" bravely wrote to "All" (01 Jul 05 06:30:35) --- on the heady topic of " Weird Microwave problem - trips breaker when you shut the door!" JS From: "James Sweet" JS Xref: aeinews sci.electronics.repair:52068 JS "Travis Evans" wrote in message JS news:6MYwe.6412$Eo.1948@fed1read04... Since virtually all microwaves now seem to be run by electronics, I wonder why they don't just program the CPU to detect interlock failures and go into an error condition and refuse to operate, instead of shorting the AC line? That would sound a lot safer to me. Then again, I'm not an expert, so maybe I'm missing something. JS Then you're relying on all the electronics to be functional as well as JS the software to be bug free, in real life there's just way too many JS chances for that to not work. They've been doing it the way they do for JS 30 years now and I've not heard of a single safety issue coming up in JS relation to that. Software isn't as unreliable as you infer since there are planes which operate "fly by wire" over our heads at this very instant. Hundreds of millions of passengers per year are trusting their lives to a line of code translated to 1's and 0's. These FBW planes even use joysticks! Like it or not, the world is now a giant video game... PONG rulz! SG OK, next time I want to spend $20,000,000 for a microwave oven I'll SG keep that in mind. :) Oh, be serious! The door interlock mechanism is an inherited safety device from the era when microwave ovens were controlled by what was basically a washing machine timer switch. The door could be easily monitored by an optical sensor. If the beam doesn't line up the microcontroller doesn't power the magnetron. That's about 1 line of code and no way would it cost $20,000,000 to do that! A*s*i*m*o*v .... Puddy-tat's not so bwave in Gwanny's microwave! |
"James Sweet" bravely wrote to "All" (01 Jul 05 23:59:06)
--- on the heady topic of " Weird Microwave problem - trips breaker when you shut the door!" JS From: "James Sweet" JS Xref: aeinews sci.electronics.repair:52141 JS The process of designing, writing and most importantly, testing the JS software used in an aircraft are completely different from that for the JS firmware in a microwave oven. There's just no comparison. I feel you are exagerating somewhat. True there is no comparison between the two but the principles are the same. Both use positive goal oriented programming where error checking and input validation is often an after thought. The truth is that "****" happens and both have no way to handle "it" when "it" does. Hell, even with human pilots at the controls they still managed to crash them without help of software. A*s*i*m*o*v .... 'Keep the smoke inside.' -- 1st Rule of Electronics. |
"Asimov" writes:
"Sam Goldwasser" bravely wrote to "All" (01 Jul 05 14:35:24) --- on the heady topic of " Weird Microwave problem - trips breaker when you shut the door!" SG From: Sam Goldwasser SG Xref: aeinews sci.electronics.repair:52109 SG "Asimov" writes: "James Sweet" bravely wrote to "All" (01 Jul 05 06:30:35) --- on the heady topic of " Weird Microwave problem - trips breaker when you shut the door!" JS From: "James Sweet" JS Xref: aeinews sci.electronics.repair:52068 JS "Travis Evans" wrote in message JS news:6MYwe.6412$Eo.1948@fed1read04... Since virtually all microwaves now seem to be run by electronics, I wonder why they don't just program the CPU to detect interlock failures and go into an error condition and refuse to operate, instead of shorting the AC line? That would sound a lot safer to me. Then again, I'm not an expert, so maybe I'm missing something. JS Then you're relying on all the electronics to be functional as well as JS the software to be bug free, in real life there's just way too many JS chances for that to not work. They've been doing it the way they do for JS 30 years now and I've not heard of a single safety issue coming up in JS relation to that. Software isn't as unreliable as you infer since there are planes which operate "fly by wire" over our heads at this very instant. Hundreds of millions of passengers per year are trusting their lives to a line of code translated to 1's and 0's. These FBW planes even use joysticks! Like it or not, the world is now a giant video game... PONG rulz! SG OK, next time I want to spend $20,000,000 for a microwave oven I'll SG keep that in mind. :) Oh, be serious! The door interlock mechanism is an inherited safety device from the era when microwave ovens were controlled by what was basically a washing machine timer switch. The door could be easily monitored by an optical sensor. If the beam doesn't line up the microcontroller doesn't power the magnetron. That's about 1 line of code and no way would it cost $20,000,000 to do that! And what happens if the software has a bug is gets kicked into a funny state by a power glitch? Hypothetical product recall notice for the HiTeck Internet-Ready MicroNuke 1: "We have determined that a particular key combination will allow the oven to run with the door open. If you've already experienced this, We sincerely hope you haven't put your head inside to try to figure out what was going on. Owners are requested to return the ovens for a software upgrade or to cut off the power cords and throw them away. The software upgrade may also be downloaded from our Web site. We believe this will solve the problem but of course, bugs are to software like flies are to honey." --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
"Asimov" wrote in message ... Oh, be serious! The door interlock mechanism is an inherited safety device from the era when microwave ovens were controlled by what was basically a washing machine timer switch. The door could be easily monitored by an optical sensor. If the beam doesn't line up the microcontroller doesn't power the magnetron. That's about 1 line of code and no way would it cost $20,000,000 to do that! Would you like to rely on this line of code when your 4 year old gets up the heat her breakfast? Buggered if I would. Even elevators with 100+ years of debugging kill people every year. I don't want my kid's eyesight ruined because some slave in a Chinese factory coughed at the wrong moment. N |
And what happens if the software has a bug is gets kicked into a funny state by a power glitch? Hypothetical product recall notice for the HiTeck Internet-Ready MicroNuke 1: "We have determined that a particular key combination will allow the oven to run with the door open. If you've already experienced this, We sincerely hope you haven't put your head inside to try to figure out what was going on. Owners are requested to return the ovens for a software upgrade or to cut off the power cords and throw them away. The software upgrade may also be downloaded from our Web site. We believe this will solve the problem but of course, bugs are to software like flies are to honey." The power glitch issue is the most realistic problem, as a user of microcontrollers in my own projects, I've had to track down some really obscure bugs where a program would get in a state that it should never be able to get into, a random bit gets flipped somehow in a register and suddenly the program is doing very strange things and it's difficult to pinpoint why it got there. In the end, nothing beats the dependability of a time proven mechanical interlock. You need the microswitches anyway, may as well have them work directly with the power rather than interface to it through other components. As someone else mentioned, the triacs that control power to the magnetron can and do fail, usually shorted which would disable even the most stable software control. The present design is cheap, effective and reliable, there's just no good reason to change it. |
James Sweet wrote:
Then you're relying on all the electronics to be functional as well as the software to be bug free, in real life there's just way too many chances for that to not work. They've been doing it the way they do for 30 years now and I've not heard of a single safety issue coming up in relation to that. You all have some good points. I do agree that mechanical safety devices should be used as well. For instance, microwaves should (if they don't already) physically disconnect the magnetron from the circuit if the door is open so that even if the microprocessor tries to turn it on, it can't. The reason I brought that up was that it seemed strange to protect against microwave exposure by using something that seemed equally dangerous: a short circuit. Also, I remembered reading somewhere (probably either here or on the alt.home.repair group) that aging circuit breakers might fail to trip when they should. That may not be true, but I couldn't help wondering what would happen if for some reason the breaker didn't trip. So I assume that all microwaves also have internal fuses which should at least blow in that situation. -- Travis Evans [The email address on this post is valid, but may change from time to time. Make sure you use the latest email address; if you use an old one, I will not receive your message.] |
Travis Evans writes:
James Sweet wrote: Then you're relying on all the electronics to be functional as well as the software to be bug free, in real life there's just way too many chances for that to not work. They've been doing it the way they do for 30 years now and I've not heard of a single safety issue coming up in relation to that. You all have some good points. I do agree that mechanical safety devices should be used as well. For instance, microwaves should (if they don't already) physically disconnect the magnetron from the circuit if the door is open so that even if the microprocessor tries to turn it on, it can't. The reason I brought that up was that it seemed strange to protect against microwave exposure by using something that seemed equally dangerous: a short circuit. Also, I remembered reading somewhere (probably either here or on the alt.home.repair group) that aging circuit breakers might fail to trip when they should. That may not be true, but I couldn't help wondering what would happen if for some reason the breaker didn't trip. So I assume that all microwaves also have internal fuses which should at least blow in that situation. Yes. --- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/ Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/ +Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm | Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html Note: These links are hopefully temporary until we can sort out the excessive traffic on Repairfaq.org. Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
Note that the Therac25 was developed from an earlier machine which had
mechanical interlocks and when you pressed the same combination of back spaces did blow a fuse, possibly 100's of people where over exposed from what I remember and several fatally or damaged for life. Do you remember in the 80's or 90's when people where installing there own mobile phones in cars and where being warned it could mess up the ABS and engine management causing accidents. Then there was the F*rd Probe car which had a problem with the ECU which meant interference from the ignition system could cause it to accelerate out of control, a man was killed when his car flew off an off ramp at over a 120 miles and hour into trees. As for the $20,000,000 planes don't they have more than one computer for all the main systems with the software written by different companies, and the computers keep a check on each other to make sure they are both working. Paul "Asimov" wrote in message ... "James Sweet" bravely wrote to "All" (01 Jul 05 23:59:06) --- on the heady topic of " Weird Microwave problem - trips breaker when you shut the door!" JS From: "James Sweet" JS Xref: aeinews sci.electronics.repair:52141 JS The process of designing, writing and most importantly, testing the JS software used in an aircraft are completely different from that for the JS firmware in a microwave oven. There's just no comparison. I feel you are exagerating somewhat. True there is no comparison between the two but the principles are the same. Both use positive goal oriented programming where error checking and input validation is often an after thought. The truth is that "****" happens and both have no way to handle "it" when "it" does. Hell, even with human pilots at the controls they still managed to crash them without help of software. A*s*i*m*o*v ... 'Keep the smoke inside.' -- 1st Rule of Electronics. |
I think that was covered on the very first post. Perhaps there is
nothing wrong with the microwave! By the way, anybody else wire up a Heathkit microwave oven way back then?? The year was 1971 I think. I was saving big bucks for buying that $400 kit!! I still think a simple rotating dial is the ultimate control for simplicity and speed. greg |
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