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#1
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Microwave failure modes - and fuse types
In my holiday flat there's a Neff built-in combi-microwave which I
believe to be about 10 years old. The microwave section has just failed, although the grill function still works. On investigation, I found a blown fuse behind the control panel. It's a glass fuse - 20mm long x 5mm dia - and is rated at 250v 10A. The actual marking says M10D. The M apparently means medium speed to blow - somewhere between an F (fast blow) and T (slow blow - time delay). I've no idea what the D signifies. Two questions: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? [Fuses *can* die of old age, but what else may have caused it?] 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. |
#2
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Microwave failure modes - and fuse types
On Jul 27, 10:35*am, Roger Mills wrote:
In my holiday flat there's a Neff built-in combi-microwave which I believe to be about 10 years old. The microwave section has just failed, although the grill function still works. On investigation, I found a blown fuse behind the control panel. It's a glass fuse - 20mm long x 5mm dia - and is rated at 250v 10A. The actual marking says M10D. The M apparently means medium speed to blow - somewhere between an F (fast blow) and T (slow blow - time delay). I've no idea what the D signifies. Two questions: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? [Fuses *can* die of old age, but what else may have caused it?] 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. Something's not right with this picture. A microwave shuold not use a glass fuse, they need the rupturing capacity of a sand filled ceramic fuse. NT |
#3
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Microwave failure modes - and fuse types
On 27/07/2011 13:06, NT wrote:
On Jul 27, 10:35 am, Roger wrote: In my holiday flat there's a Neff built-in combi-microwave which I believe to be about 10 years old. The microwave section has just failed, although the grill function still works. On investigation, I found a blown fuse behind the control panel. It's a glass fuse - 20mm long x 5mm dia - and is rated at 250v 10A. The actual marking says M10D. The M apparently means medium speed to blow - somewhere between an F (fast blow) and T (slow blow - time delay). I've no idea what the D signifies. Two questions: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? [Fuses *can* die of old age, but what else may have caused it?] 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. Something's not right with this picture. A microwave shuold not use a glass fuse, they need the rupturing capacity of a sand filled ceramic fuse. NT It's possible that the fuse which blew was not the original - I haven't owned the device from new. But the markings on the PCB next to the fuse-holder say F1[1] and M10. What are the special characteristics of a sand filled ceramic fuse? I can certainly get some from Maplin which would fit - but would they fail to provide adequate protection in some other way? [1] Presumably Fuse 1 - there's another 1 amp stripy fuse labelled F2, which *didn't* blow -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. |
#4
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Microwave failure modes - and fuse types
On Jul 27, 1:40*pm, Roger Mills wrote:
On 27/07/2011 13:06, NT wrote: On Jul 27, 10:35 am, Roger *wrote: In my holiday flat there's a Neff built-in combi-microwave which I believe to be about 10 years old. The microwave section has just failed, although the grill function still works. On investigation, I found a blown fuse behind the control panel. It's a glass fuse - 20mm long x 5mm dia - and is rated at 250v 10A. The actual marking says M10D. The M apparently means medium speed to blow - somewhere between an F (fast blow) and T (slow blow - time delay). I've no idea what the D signifies. Two questions: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? [Fuses *can* die of old age, but what else may have caused it?] 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. Something's not right with this picture. A microwave shuold not use a glass fuse, they need the rupturing capacity of a sand filled ceramic fuse. NT It's possible that the fuse which blew was not the original - I haven't owned the device from new. But the markings on the PCB next to the fuse-holder say F1[1] and M10. What are the special characteristics of a sand filled ceramic fuse? I can certainly get some from Maplin which would fit - but would they fail to provide adequate protection in some other way? [1] Presumably Fuse 1 - there's another 1 amp stripy fuse labelled F2, which *didn't* blow Sand filled ceramics have much higher rupturing capacity than glass fuses. And the consequence of failure to blow isnt just electrical, but potentially severe internal burns of the end user. NT |
#5
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Microwave failure modes - and fuse types
"Roger Mills" wrote in message ... On 27/07/2011 13:06, NT wrote: On Jul 27, 10:35 am, Roger wrote: In my holiday flat there's a Neff built-in combi-microwave which I believe to be about 10 years old. The microwave section has just failed, although the grill function still works. On investigation, I found a blown fuse behind the control panel. It's a glass fuse - 20mm long x 5mm dia - and is rated at 250v 10A. The actual marking says M10D. The M apparently means medium speed to blow - somewhere between an F (fast blow) and T (slow blow - time delay). I've no idea what the D signifies. Two questions: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? [Fuses *can* die of old age, but what else may have caused it?] 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. Something's not right with this picture. A microwave shuold not use a glass fuse, they need the rupturing capacity of a sand filled ceramic fuse. NT It's possible that the fuse which blew was not the original - I haven't owned the device from new. But the markings on the PCB next to the fuse-holder say F1[1] and M10. What are the special characteristics of a sand filled ceramic fuse? I can certainly get some from Maplin which would fit - but would they fail to provide adequate protection in some other way? [1] Presumably Fuse 1 - there's another 1 amp stripy fuse labelled F2, which *didn't* blow -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. I've seen glass fuses on the mains input of microwaves, although equally, ceramics are also quite common. Check to make sure that nothing has happened to the door interlock switch mechanism. One of the switches places a short across the output of the other one when the door is opened. It's a sort of 'belt and braces' thing. One switch opens to isolate the supply when the door opens, and the other closes to place a short across the open one, just in case it hasn't opened. The fuse-blowing situation can occur if the switch contacts on either one weld themselves up, or if a switch comes loose on its bracket, or the mech that works it breaks. You would be ok with a T rated fuse. If you want to put a ceramic in, you should be able to get a T10A without too much problem. Arfa |
#6
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Microwave failure modes - and fuse types
On Jul 27, 3:44*pm, "Arfa Daily" wrote:
"Roger Mills" wrote in message ... On 27/07/2011 13:06, NT wrote: On Jul 27, 10:35 am, Roger *wrote: In my holiday flat there's a Neff built-in combi-microwave which I believe to be about 10 years old. The microwave section has just failed, although the grill function still works. On investigation, I found a blown fuse behind the control panel. It's a glass fuse - 20mm long x 5mm dia - and is rated at 250v 10A. The actual marking says M10D. The M apparently means medium speed to blow - somewhere between an F (fast blow) and T (slow blow - time delay). I've no idea what the D signifies. Two questions: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? [Fuses *can* die of old age, but what else may have caused it?] 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. Something's not right with this picture. A microwave shuold not use a glass fuse, they need the rupturing capacity of a sand filled ceramic fuse. NT It's possible that the fuse which blew was not the original - I haven't owned the device from new. But the markings on the PCB next to the fuse-holder say F1[1] and M10. What are the special characteristics of a sand filled ceramic fuse? I can certainly get some from Maplin which would fit - but would they fail to provide adequate protection in some other way? [1] Presumably Fuse 1 - there's another 1 amp stripy fuse labelled F2, which *didn't* blow -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. I've seen glass fuses on the mains input of microwaves, although equally, ceramics are also quite common. Check to make sure that nothing has happened to the door interlock switch mechanism. One of the switches places a short across the output of the other one when the door is opened. It's a sort of 'belt and braces' thing. One switch opens to isolate the supply when the door opens, and the other closes to place a short across the open one, just in case it hasn't opened. The fuse-blowing situation can occur if the switch contacts on either one weld themselves up, or if a switch comes loose on its bracket, or the mech that works it breaks. You would be ok with a T rated fuse. If you want to put a ceramic in, you should be able to get a T10A without too much problem. Arfa- Hide quoted text - - Show quoted text - Not the fuse the OP is describing but there is usually a glass fuse on the HV side of the microwave. My microwave has just failed and I found this fuse had blown. I replaced it with a fuse off Ebay (there are lots to choose from). Unfortunately the problem is more severe than a blown fuse as the replacement also blew. So I guess the is a fault with the magnetron circuit. When time permits I will be stripping the microwave down to see what failed out of interest. A word of warning, don't fiddle around in the microwave circuits unless you know which bits not to go near. |
#7
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Microwave failure modes - and fuse types
On Wed, 27 Jul 2011 10:35:40 +0100, Roger Mills
wrote: On investigation, I found a blown fuse behind the control panel. It's a glass fuse - 20mm long x 5mm dia - and is rated at 250v 10A. Since the fuse is/was glass, was the glass blackened or sprayed with metal internally? If so then "something" has blown it and the replacement you buy will blow as well. If not then it /may/ have been just tired of life. |
#8
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Microwave failure modes - and fuse types
On 27/07/2011 15:36, NT wrote:
Sand filled ceramics have much higher rupturing capacity than glass fuses. Sorry, I'm not sure I understand the term "rupturing capacity". Are you talking about the physical disintegration of the glass (or whatever) tube - or simply about the overload current which can be sustained before it blows? And the consequence of failure to blow isnt just electrical, but potentially severe internal burns of the end user. I'm not sure I understand that either! What circumstances do you have in mind? -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. |
#9
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Microwave failure modes - and fuse types
On Jul 27, 5:02*pm, Roger Mills wrote:
On 27/07/2011 15:36, NT wrote: Sand filled ceramics have much higher rupturing capacity than glass fuses. Sorry, I'm not sure I understand the term "rupturing capacity". Are you talking about the physical disintegration of the glass (or whatever) tube - or simply about the overload current which can be sustained before it blows? Putting it simply, the current which occurs if there is a short circuit may be many times higher than the rated capacity of the fuse (which is the maximum current it can pass indefinitely), and the rupturing capacity is the current the fuse can safely break. When the fuse blows there will be a momentary arc between the ends of the fuse element, and for higher rupturing capacity fuses the sand fill helps to extinguish this safely. As an indication, the standard BS1362 fuses used in UK 13 Amp plugs have a rupturing capacity of 6000A, while glass fuses can only break currents of the order of 100A. There's lots more at http://wiki.diyfaq.org.uk/index.php?title=Fuse. Mike |
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Microwave failure modes - and fuse types
On Jul 27, 1:40*pm, Roger Mills wrote:
What are the special characteristics of a sand filled ceramic fuse? High rupturing capacity - the ability to interrupt a large fault current and isolate it quickly, rather than allowing an arc to be sustained across the ends of the melted wire. Mostly an issue for high voltage or inductive loads - for a 20mm fuse, inductive loads, such as a big transformer, are the likely reason. |
#11
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Microwave failure modes - and fuse types
On Jul 27, 5:02*pm, Roger Mills wrote:
On 27/07/2011 15:36, NT wrote: Sand filled ceramics have much higher rupturing capacity than glass fuses. Sorry, I'm not sure I understand the term "rupturing capacity". Are you talking about the physical disintegration of the glass (or whatever) tube - or simply about the overload current which can be sustained before it blows? neither. If fault current is above the rupturing capacity of the fuse, the fuse cant break the circuit. * And the consequence of failure to blow isnt just electrical, but potentially severe internal burns of the end user. I'm not sure I understand that either! What circumstances do you have in mind? Interlock failure causes fuse blows. If the fuse doesnt blow, then a faulty interlock means sometimes the thing will cook with the door open. Unless you want to be food, thats not a good idea. If the main fuse blows, always check the shorting resistor. Sometimes that also fails, and sometimes that means no working protection circuitry, but it still cooks. NT |
#12
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Microwave failure modes - and fuse types
On Wed, 27 Jul 2011 10:35:40 +0100, Roger Mills
wrote: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? Quite good, certainly worth a try. One other failure mode which can occur and will blow the fuse is that the door micro switches fail - not usually difficult to diagnose or fix. 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. Any slow blow or time fuse is fine. Even if the fuse ruptures the microwave case will contain the glass fragments. |
#13
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Microwave failure modes - and fuse types
On 27/07/2011 16:46, Geo wrote:
On Wed, 27 Jul 2011 10:35:40 +0100, Roger wrote: On investigation, I found a blown fuse behind the control panel. It's a glass fuse - 20mm long x 5mm dia - and is rated at 250v 10A. Since the fuse is/was glass, was the glass blackened or sprayed with metal internally? If so then "something" has blown it and the replacement you buy will blow as well. If not then it /may/ have been just tired of life. It's blackened for about 80% of the length of the visible glass envelope - suggesting a rapid overload. Other posts are suggesting that this could possibly be caused by a problem with the interlock switches on the door. I will investigate next time I'm at the flat. The only problem is that it's mounted quite up in a built-in unit - above a conventional oven - and it's bl**dy heavy! -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. |
#14
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Microwave failure modes - and fuse types
"Peter Parry" wrote in message news On Wed, 27 Jul 2011 10:35:40 +0100, Roger Mills wrote: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? Quite good, certainly worth a try. One other failure mode which can occur and will blow the fuse is that the door micro switches fail - not usually difficult to diagnose or fix. 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. Any slow blow or time fuse is fine. Even if the fuse ruptures the microwave case will contain the glass fragments. As the glass fuse did not vaporise and was only partially blackened I suspect the door microswitches did not crowbar the supply (but if it tripped the MCB as well then I wouldn't be so sure) I think it is more likely to be, in order of likleynes: HV diode short-circuit HV capacitor short-circuit Magnetron cathode (filament) to anode (chassis earth) short circuit. Generally speaking a microwave can run for a long time with any of the above faults without blowing the mains fuse, because the transformer is run at near saturation so there isn't as great an increase in primary current as you might imagine. Apart from not heating the food the only symptom is a slightly louder buzz from the tranny than normal. Microwave ovens are one of the easiest of domestic appliances to fault-find and repair IIHO, (Panasonic inverter models exempted!) *Unplug* from mains and *discharge* the big HV capacitor with a couple of well insulated screwdrivers before delving inside, I can't emphasise those enough. Use a multimeter on ohms range to test the components above. -- Graham. %Profound_observation% |
#15
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Microwave failure modes - and fuse types
"Graham." wrote in message ... "Peter Parry" wrote in message news On Wed, 27 Jul 2011 10:35:40 +0100, Roger Mills wrote: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? Quite good, certainly worth a try. One other failure mode which can occur and will blow the fuse is that the door micro switches fail - not usually difficult to diagnose or fix. 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. Any slow blow or time fuse is fine. Even if the fuse ruptures the microwave case will contain the glass fragments. As the glass fuse did not vaporise and was only partially blackened I suspect the door microswitches did not crowbar the supply (but if it tripped the MCB as well then I wouldn't be so sure) I think it is more likely to be, in order of likleynes: HV diode short-circuit HV capacitor short-circuit Magnetron cathode (filament) to anode (chassis earth) short circuit. Generally speaking a microwave can run for a long time with any of the above faults without blowing the mains fuse, because the transformer is run at near saturation so there isn't as great an increase in primary current as you might imagine. Apart from not heating the food the only symptom is a slightly louder buzz from the tranny than normal. Microwave ovens are one of the easiest of domestic appliances to fault-find and repair IIHO, (Panasonic inverter models exempted!) *Unplug* from mains and *discharge* the big HV capacitor with a couple of well insulated screwdrivers before delving inside, I can't emphasise those enough. Use a multimeter on ohms range to test the components above. -- Graham. Understanding, of course, that a conventional multimeter is unlikely to produce enough voltage on any of its ohms ranges, to turn on the HV diode, so this device is likely to read open circuit, even if it's ok ... Agreed though, that a short circuit diode will be picked up ok. Arfa |
#16
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Microwave failure modes - and fuse types
"Graham." writes:
*Unplug* from mains and *discharge* the big HV capacitor with a couple of well insulated screwdrivers before delving inside, I can't emphasise those enough. Use a multimeter on ohms range to test the components above. But bear in mind that the diode is likely to be actually about 10 diodes in series, so if it's OK it won't conduct in either direction unless the multimeter applies a voltage of more than maybe 6 volts. That fooled me once into thinking that the diode was open-circuit. (The meter, not my own, had only a 1.5 volt battery.) -- Windmill, Use t m i l l @ O n e t e l . c o m |
#17
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Microwave failure modes - and fuse types
"Arfa Daily" wrote in message ... "Graham." wrote in message ... "Peter Parry" wrote in message news On Wed, 27 Jul 2011 10:35:40 +0100, Roger Mills wrote: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? Quite good, certainly worth a try. One other failure mode which can occur and will blow the fuse is that the door micro switches fail - not usually difficult to diagnose or fix. 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. Any slow blow or time fuse is fine. Even if the fuse ruptures the microwave case will contain the glass fragments. As the glass fuse did not vaporise and was only partially blackened I suspect the door microswitches did not crowbar the supply (but if it tripped the MCB as well then I wouldn't be so sure) I think it is more likely to be, in order of likleynes: HV diode short-circuit HV capacitor short-circuit Magnetron cathode (filament) to anode (chassis earth) short circuit. Generally speaking a microwave can run for a long time with any of the above faults without blowing the mains fuse, because the transformer is run at near saturation so there isn't as great an increase in primary current as you might imagine. Apart from not heating the food the only symptom is a slightly louder buzz from the tranny than normal. Microwave ovens are one of the easiest of domestic appliances to fault-find and repair IIHO, (Panasonic inverter models exempted!) *Unplug* from mains and *discharge* the big HV capacitor with a couple of well insulated screwdrivers before delving inside, I can't emphasise those enough. Use a multimeter on ohms range to test the components above. -- Graham. Understanding, of course, that a conventional multimeter is unlikely to produce enough voltage on any of its ohms ranges, to turn on the HV diode, so this device is likely to read open circuit, even if it's ok ... The HV is the reverse voltage that the diode is rated at, not forward voltage, so you can still check it with a multimeter. |
#18
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Microwave failure modes - and fuse types
"Mr. Benn" wrote in message ... "Arfa Daily" wrote in message ... "Graham." wrote in message ... "Peter Parry" wrote in message news On Wed, 27 Jul 2011 10:35:40 +0100, Roger Mills wrote: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? Quite good, certainly worth a try. One other failure mode which can occur and will blow the fuse is that the door micro switches fail - not usually difficult to diagnose or fix. 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. Any slow blow or time fuse is fine. Even if the fuse ruptures the microwave case will contain the glass fragments. As the glass fuse did not vaporise and was only partially blackened I suspect the door microswitches did not crowbar the supply (but if it tripped the MCB as well then I wouldn't be so sure) I think it is more likely to be, in order of likleynes: HV diode short-circuit HV capacitor short-circuit Magnetron cathode (filament) to anode (chassis earth) short circuit. Generally speaking a microwave can run for a long time with any of the above faults without blowing the mains fuse, because the transformer is run at near saturation so there isn't as great an increase in primary current as you might imagine. Apart from not heating the food the only symptom is a slightly louder buzz from the tranny than normal. Microwave ovens are one of the easiest of domestic appliances to fault-find and repair IIHO, (Panasonic inverter models exempted!) *Unplug* from mains and *discharge* the big HV capacitor with a couple of well insulated screwdrivers before delving inside, I can't emphasise those enough. Use a multimeter on ohms range to test the components above. -- Graham. Understanding, of course, that a conventional multimeter is unlikely to produce enough voltage on any of its ohms ranges, to turn on the HV diode, so this device is likely to read open circuit, even if it's ok ... The HV is the reverse voltage that the diode is rated at, not forward voltage, so you can still check it with a multimeter. The depletion voltage required to forward bias the diode is going to be many times higher than the typical 0.7v for a single silicon junction. -- Graham. %Profound_observation% |
#19
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Microwave failure modes - and fuse types
Vf is 12 volts on this diode http://pdf1.alldatasheet.com/datashe...VR-1X-01A.html so a popular multimeter with a PP3 battery won't forward bias it. An old Avo 8 on the other hand might just do it. I think they go very leaky rather than OC -- Graham. %Profound_observation% |
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Microwave failure modes - and fuse types - UPDATE
On 27/07/2011 10:35, Roger Mills wrote:
In my holiday flat there's a Neff built-in combi-microwave which I believe to be about 10 years old. The microwave section has just failed, although the grill function still works. On investigation, I found a blown fuse behind the control panel. It's a glass fuse - 20mm long x 5mm dia - and is rated at 250v 10A. The actual marking says M10D. The M apparently means medium speed to blow - somewhere between an F (fast blow) and T (slow blow - time delay). I've no idea what the D signifies. Two questions: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? [Fuses *can* die of old age, but what else may have caused it?] 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. I'm now back at the flat, and have done the following: 1. Replaced the blown fuse with a 10A ceramic jobbie. The result was that the panel lit up again, and I could open and close the door without problem. However when I tried to operate the microwave (on its second from highest setting) the internal light came on as normal, it made encouraging noises (albeit a bit louder than usual) for a few seconds and then the fuse blew again. 2. I then tried a T10 glass fuse. The panel lit up again and opening and closing the door was again ok. This time, I tried operating the microwave on its lowest setting - and it ran for the time I had set (about 15 seconds) without problems. I then tried it on its second from lowest setting, and the fuse immediately blew! Does this additional information help to narrow down the likely underlying problem? -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. |
#21
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Microwave failure modes - and fuse types - UPDATE
Roger Mills wrote:
On 27/07/2011 10:35, Roger Mills wrote: In my holiday flat there's a Neff built-in combi-microwave which I believe to be about 10 years old. The microwave section has just failed, although the grill function still works. On investigation, I found a blown fuse behind the control panel. It's a glass fuse - 20mm long x 5mm dia - and is rated at 250v 10A. The actual marking says M10D. The M apparently means medium speed to blow - somewhere between an F (fast blow) and T (slow blow - time delay). I've no idea what the D signifies. Two questions: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? [Fuses *can* die of old age, but what else may have caused it?] 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. I'm now back at the flat, and have done the following: 1. Replaced the blown fuse with a 10A ceramic jobbie. The result was that the panel lit up again, and I could open and close the door without problem. However when I tried to operate the microwave (on its second from highest setting) the internal light came on as normal, it made encouraging noises (albeit a bit louder than usual) for a few seconds and then the fuse blew again. 2. I then tried a T10 glass fuse. The panel lit up again and opening and closing the door was again ok. This time, I tried operating the microwave on its lowest setting - and it ran for the time I had set (about 15 seconds) without problems. I then tried it on its second from lowest setting, and the fuse immediately blew! Does this additional information help to narrow down the likely underlying problem? Time to take the wife shopping for a new one:-)? -- Adam |
#22
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Microwave failure modes - and fuse types - UPDATE
On 23/08/2011 21:58, ARWadsworth wrote:
Roger wrote: On 27/07/2011 10:35, Roger Mills wrote: In my holiday flat there's a Neff built-in combi-microwave which I believe to be about 10 years old. The microwave section has just failed, although the grill function still works. On investigation, I found a blown fuse behind the control panel. It's a glass fuse - 20mm long x 5mm dia - and is rated at 250v 10A. The actual marking says M10D. The M apparently means medium speed to blow - somewhere between an F (fast blow) and T (slow blow - time delay). I've no idea what the D signifies. Two questions: 1. Since *something* must have caused the fuse to blow, what's the likelihood that replacing the fuse will fix it? [Fuses *can* die of old age, but what else may have caused it?] 2. Since I can't find an identical use, what's the best type to use? Maplins have T10's and also some ceramic jobbies - apparently intended for microwaves. I'm now back at the flat, and have done the following: 1. Replaced the blown fuse with a 10A ceramic jobbie. The result was that the panel lit up again, and I could open and close the door without problem. However when I tried to operate the microwave (on its second from highest setting) the internal light came on as normal, it made encouraging noises (albeit a bit louder than usual) for a few seconds and then the fuse blew again. 2. I then tried a T10 glass fuse. The panel lit up again and opening and closing the door was again ok. This time, I tried operating the microwave on its lowest setting - and it ran for the time I had set (about 15 seconds) without problems. I then tried it on its second from lowest setting, and the fuse immediately blew! Does this additional information help to narrow down the likely underlying problem? Time to take the wife shopping for a new one:-)? Possibly. Problem is that it's a built-in combi microwave (which are ridiculously expensive compared with free-standing ones[1], it's not a current model (about 11 years old, at a guess) and there's a matching single oven - so a new one ain't quite going to match, even if it fits the space! It would be better to mend it if it doesn't cost the earth. [1] A Neff built-in combi is of the order of £400, whereas Lidl have got a free-standing microwave with grill on offer at £40 on Thursday! -- Cheers, Roger ____________ Please reply to Newsgroup. Whilst email address is valid, it is seldom checked. |
#23
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Microwave failure modes - and fuse types - UPDATE
"Roger Mills" wrote in message ... On 27/07/2011 10:35, Roger Mills wrote: In my holiday flat there's a Neff built-in combi-microwave which I snipped The panel lit up again and opening and closing the door was again ok. This time, I tried operating the microwave on its lowest setting - and it ran for the time I had set (about 15 seconds) without problems. I then tried it on its second from lowest setting, and the fuse immediately blew! Does this additional information help to narrow down the likely underlying problem? Cheers, Roger Start with a word of warning. Never operate a microwave oven while it is empty. Always have, at least, a half cup of water inside. Also, unless stated on the front of the oven, never put metal inside the oven. Not even crockery (plates, cups, saucers etc.) with metallic design features. Another very common microwave oven killer, is the frozen pack of Sunday Bacon, which often contains metal foil in the packaging and is thrown in the micro' to defrost. Microwave Ovens don't really have a low, medium or high setting, they only have "ON" or "OFF" periods for set times, depending on which option you choose. Setting the oven on low, and only running it for a short time set, may not have been long enough to show a fault. Example: High setting starts the oven immediately, and remains on until the set time expires. Medium starts the oven immediately, but only runs for, let's say, 10 seconds, then it switches off for a few seconds, then back on again, until the set time runs down. Low setting may not start the heating cycle for a few seconds, then it will cycle the on / off periods even more frequently, thus giving the food only short blasts of energy at a time, rather than constantly like the high setting would. My advice would be. Unplug the oven from the mains. Look inside at the walls, roof and around the base for any small scorch marks left by arcing metal which may have inadvertently been placed in the oven. The marks could be as small as a group of black dots, like ink dawbs from a ball-point pen. If you do see marks like that, then get a new oven. The wave guide has probably been blackened and will, more than likely, not be repairable. Replacing the whole 'innards will be more expensive than a new oven. If you don't see marks on the inside of the oven, and make sure you have checked it thoroughly, then a repair, to something simple like the timer or control circuit, may not be an expensive option. Choose a reputable engineer for these types of repair, as a bodge can seriously damage health and damage property. Who knows, it could be something silly like beef fat dripped across the turntable motor. But I am not going advise that you take this type of appliance apart by yourself. They contain large amounts of stored energy, even when unplugged and lying dormant for years, and can kill very easily. So get the Yellow Pages out. Good luck with it. --- Posted via news://freenews.netfront.net/ - Complaints to --- |
#24
Posted to uk.d-i-y
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Microwave failure modes - and fuse types - UPDATE
On Aug 24, 4:53*am, "BigWallop" wrote:
"Roger Mills" wrote in message ... On 27/07/2011 10:35, Roger Mills wrote: In my holiday flat there's a Neff built-in combi-microwave which I snipped The panel lit up again and opening and closing the door was again ok. This time, I tried operating the microwave on its lowest setting - and it ran for the time I had set (about 15 seconds) without problems. I then tried it on its second from lowest setting, and the fuse immediately blew! Does this additional information help to narrow down the likely underlying problem? Cheers, Roger Start with a word of warning. *Never operate a microwave oven while it is empty. *Always have, at least, a half cup of water inside. *Also, unless stated on the front of the oven, never put metal inside the oven. *Not even crockery (plates, cups, saucers etc.) with metallic design features. Another very common microwave oven killer, is the frozen pack of Sunday Bacon, which often contains metal foil in the packaging and is thrown in the micro' to defrost. Microwave Ovens don't really have a low, medium or high setting, they only have "ON" or "OFF" periods for set times, depending on which option you choose. *Setting the oven on low, and only running it for a short time set, may not have been long enough to show a fault. Example: High setting starts the oven immediately, and remains on until the set time expires. Medium starts the oven immediately, but only runs for, let's say, 10 seconds, then it switches off for a few seconds, then back on again, until the set time runs down. Low setting may not start the heating cycle for a few seconds, then it will cycle the on / off periods even more frequently, thus giving the food only short blasts of energy at a time, rather than constantly like the high setting would. My advice would be. *Unplug the oven from the mains. *Look inside at the walls, roof and around the base for any small scorch marks left by arcing metal which may have inadvertently been placed in the oven. *The marks could be as small as a group of black dots, like ink dawbs from a ball-point pen. |
#25
Posted to uk.d-i-y
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Microwave failure modes - and fuse types - UPDATE
On Aug 24, 1:29*pm, whisky-dave wrote:
On Aug 24, 12:27*pm, NT wrote: On Aug 24, 4:53*am, "BigWallop" wrote: "Roger Mills" wrote in message ... On 27/07/2011 10:35, Roger Mills wrote: In my holiday flat there's a Neff built-in combi-microwave which I snipped The panel lit up again and opening and closing the door was again ok. This time, I tried operating the microwave on its lowest setting - and it ran for the time I had set (about 15 seconds) without problems. I then tried it on its second from lowest setting, and the fuse immediately blew! Does this additional information help to narrow down the likely underlying problem? Cheers, Roger Start with a word of warning. *Never operate a microwave oven while it is empty. *Always have, at least, a half cup of water inside. *Also, unless stated on the front of the oven, never put metal inside the oven. *Not even crockery (plates, cups, saucers etc.) with metallic design features. Another very common microwave oven killer, is the frozen pack of Sunday Bacon, which often contains metal foil in the packaging and is thrown in the micro' to defrost. Microwave Ovens don't really have a low, medium or high setting, they only have "ON" or "OFF" periods for set times, depending on which option you choose. *Setting the oven on low, and only running it for a short time set, may not have been long enough to show a fault. Example: High setting starts the oven immediately, and remains on until the set time expires. Medium starts the oven immediately, but only runs for, let's say, 10 seconds, then it switches off for a few seconds, then back on again, until the set time runs down. Low setting may not start the heating cycle for a few seconds, then it will cycle the on / off periods even more frequently, thus giving the food only short blasts of energy at a time, rather than constantly like the high setting would. My advice would be. *Unplug the oven from the mains. *Look inside at the walls, roof and around the base for any small scorch marks left by arcing metal which may have inadvertently been placed in the oven. *The marks could be as small as a group of black dots, like ink dawbs from a ball-point pen. If you do see marks like that, then get a new oven. *The wave guide has probably been blackened and will, more than likely, not be repairable.. Replacing the whole 'innards will be more expensive than a new oven. If you don't see marks on the inside of the oven, and make sure you have checked it thoroughly, then a repair, to something simple like the timer or control circuit, may not be an expensive option. *Choose a reputable engineer for these types of repair, as a bodge can seriously damage health and damage property. Who knows, it could be something silly like beef fat dripped across the turntable motor. *But I am not going advise that you take this type of appliance apart by yourself. *They contain large amounts of stored energy, even when unplugged and lying dormant for years, and can kill very easily. So get the Yellow Pages out. Good luck with it. Sorry but most of this is not good advice. The HV capacitor certainly can kill though. NT Seemed quite reasonable to me, although saying HV capacitors can kill is rather misleading. Cars can kill too, but it's the charge on the capacitor that can kill not the capacitor itself well unless swallowed or inserted somewhere it really shouldn't be ;-) Probaly the biggest shortcoming of this group is the tendency of people with no electronic expertise to give advice on the susject. Telling people never to operate an oven empty is a classic, it only ever applied to the very first microwave oven model many decades ago. NT |
#26
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Microwave failure modes - and fuse types - UPDATE
whisky-dave wrote:
Seemed quite reasonable to me, although saying HV capacitors can kill is rather misleading. I think the point is they can kill someone who is unaware of the charge they (can) hold even when switched off Cars can kill too, but it's the charge on the capacitor that can kill not the capacitor itself It's usually the momentum of a car that kills, not the car itself. |
#27
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Microwave failure modes - and fuse types - UPDATE
On 24 Aug,
whisky-dave wrote: Seemed quite reasonable to me, although saying HV capacitors can kill is rather misleading. Can easily be lethal to the unaware! Metal foil is often used in microwaves to shield areas where the food is thinner to avoid overcooking those parts. Generally metal isn't a problem as long as not resonant and close to other metal parts, resulting in sparking. I regularly leave the spoon in when making gravy without a problem. The majority of microwaves do pulse for lower than full power, however, my last two have used inverters and have reduced the power to the magnetron in the same way yhat switched mode power supplies regulate. The failure of the first of my inverter microwaves was due to my forgetting to add the milk/water to my porridge. It never recovered from the resultant fire. It is important that some load that will absorb the microwaves is present in the oven cavity. This is almost without exception water in a liquid form (rather than as ice which doiesn't absorb microwaes), hence adding a teaspoon of water to frozen veg before cooking. -- B Thumbs Change lycos to yahoo to reply |
#28
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Microwave failure modes - and fuse types - UPDATE
In article ,
writes: The failure of the first of my inverter microwaves was due to my forgetting to add the milk/water to my porridge. It never recovered from the resultant fire. For a few weeks, I had no kitchen due to ripping out and fitting a new one. I moved one of the floor-standing cupboards into the dining room, and stood the microwave, kettle, and toaster on it, and that was my kitchen, plus the fridge-freezer. I bought a frozen multi-pack of microwave chips, which I had a few of. However, a year or two later, I found the last one still in the freezer. Of course, it was well past its best-before date, but what can go wrong with chips? Popped them into the microwave, and switched on. Within a few seconds, they explode into flames. Manage to get them out of the microwave quickly, and only damage was an internal coating of soot, and a burning smell which took a couple of weeks to leave the house. On closer inspection, they had completely freeze-dried, leaving basically a mixture of starch powder and oil. Hence the fire. I did wonder if "best-before" was perhaps understating things. -- Andrew Gabriel [email address is not usable -- followup in the newsgroup] |
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