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OT: microwave oven blows fuse
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Hi, everybody. Has anybody else seen this issue: one day recently, out of the blue, our Kitchen Aid microwave oven stopped working. One day it was fine, and the next day the display was blank, and the keypad wouldn't respond to anything. So I attempted to open it up, thinking a catastrophic fault like this might be easy to fix. I had to go to Home Depot to get a set of those Torx drivers with the hole in the center because the screws holding the cover on are Torx with the pin in the center. Not that I mind buying a new tool, of course! So I opened it up yesterday, and sure enough, the 20 amp fuse was blown. Really, really blown - the metal inside was splattered all over the glass!
I checked YouTube, watched a few videos, and decided to discharge and measure the high voltage capacitor, a known weak point. So I grabbed some alligator clips, some banana leads, and a 2 ohm, 25 W wirewound resistor I had lying around. I didn't think discharging the cap, a 0.95 uF job, with a dead short was a good idea. The cap measured about 130 ohms and 0.00 V, but the ohms reading was very unstable. I realized the HV transformer was still in the circuit, so I disconnected the cap leads (very hard to get the clips off, BTW) and measured again. Megohms this time and about 0.2 V (I chalked that up to dielectric absorption). I figured it wasn't the cap, and maybe the original fuse was faulty or a power surge had fried it. I hoped for the best and made another trip to Home Depot and bought a ceramic fuse. Actually 2 in a pack. Put one in the microwave oven and was pleased to hear it beep and get all zeros on the display. Short lived, though, because the kitchen lights dimmed, and the display went blank. Sure enough, the fuse was open now. So, anybody have an idea what to check next? Or is the cap indeed blown and in need of replacement? I'd sure hate to have to trash this appliance after only about 4 years (1 year warranty, of course!). And I'd hate even more to have to spring for another one. IIRC, it was about $750 new. Thanks. Jim Ford in Southern California, USA |
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Bob Albert
This is a common problem.? Chances are one of three things.? Bad capacitor, bad rectifier, bad transformer.? The transformer may be arcing due to high voltage.? The same for the capacitor.? You could test the capacitor and the diode with a power supply.? Testing the transformer requires energizing it with no load to see if it withstands the voltage and has no shorted turns.
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In extreme cases it could be the magnetron. Bob On Sunday, December 12, 2021, 05:05:19 PM PST, Jim Ford <james.ford@...> wrote:
Hi, everybody.? Has anybody else seen this issue: one day recently, out of the blue, our Kitchen Aid microwave oven stopped working.? One day it was fine, and the next day the display was blank, and the keypad wouldn't respond to anything.? So I attempted to open it up, thinking a catastrophic fault like this might be easy to fix.? I had to go to Home Depot to get a set of those Torx drivers with the hole in the center because the screws holding the cover on are Torx with the pin in the center.? Not that I mind buying a new tool, of course!? So I opened it up yesterday, and sure enough, the 20 amp fuse was blown.? Really, really blown - the metal inside was splattered all over the glass! I checked YouTube, watched a few videos, and decided to discharge and measure the high voltage capacitor, a known weak point.? So I grabbed some alligator clips, some banana leads, and a 2 ohm, 25 W wirewound resistor I had lying around.? I didn't think discharging the cap, a 0.95 uF job, with a dead short was a good idea.? The cap measured about 130 ohms and 0.00 V, but the ohms reading was very unstable.? I realized the HV transformer was still in the circuit, so I disconnected the cap leads (very hard to get the clips off, BTW) and measured again.? Megohms this time and about 0.2 V (I chalked that up to dielectric absorption). I figured it wasn't the cap, and maybe the original fuse was faulty or a power surge had fried it.? I hoped for the best and made another trip to Home Depot and bought a ceramic fuse.? Actually 2 in a pack.? Put one in the microwave oven and was pleased to hear it beep and get all zeros on the display.? Short lived, though, because the kitchen lights dimmed, and the display went blank.? Sure enough, the fuse was open now. So, anybody have an idea what to check next?? Or is the cap indeed blown and in need of replacement?? I'd sure hate to have to trash this appliance after only about 4 years (1 year warranty, of course!).? And I'd hate even more to have to spring for another one.? IIRC, it was about $750 new. Thanks. Jim Ford in Southern California, USA |
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Hi Jim,
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I haven't fixed nearly as many microwaves as scopes, but more than a handful. For ovens using a traditional power supply with line-frequency magnetics, the most common failure mode is a shorted/leaky cap, and a close second is a shorted/leaky HV rectifier. It can be hard to determine the exact failure using only low-voltage gear, so a 577 curve tracer or equivalent is almost obligatory if a DMM, e.g., doesn't identify the bad component. Substitution is often the way to go if you don't have HV test gear, unless the replacement parts are ridiculously expensive. One note on the cap: Its value matters, as it is chosen to resonate with the leakage inductance of the HV transformer. -- Cheers, Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 12/12/2021 15:05, Jim Ford wrote:
Hi, everybody.? Has anybody else seen this issue: one day recently, out of the blue, our Kitchen Aid microwave oven stopped working. One day it was fine, and the next day the display was blank, and the keypad wouldn't respond to anything.? So I attempted to open it up, thinking a catastrophic fault like this might be easy to fix.? I had to go to Home Depot to get a set of those Torx drivers with the hole in the center because the screws holding the cover on are Torx with the pin in the center.? Not that I mind buying a new tool, of course!? So I opened it up yesterday, and sure enough, the 20 amp fuse was blown.? Really, really blown - the metal inside was splattered all over the glass! |
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Thanks, Tom.? Unfortunately I don't have a curve tracer, not yet anyway.? Tek 576 is on my wishlist, and I do know a guy nearby who has one in his storage unit.? But will check HV cap and diode prices meantime.? Gotta be less than a new microwave oven, at least a big fancy one like we have.? ? ?JimSent from my Verizon, Samsung Galaxy smartphone
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-------- Original message --------From: Tom Lee <tomlee@...> Date: 12/12/21 5:26 PM (GMT-08:00) To: [email protected], [email protected] Subject: Re: [TekScopes] OT: microwave oven blows fuse Hi Jim,I haven't fixed nearly as many microwaves as scopes, but more than a handful. For ovens using a traditional power supply with line-frequency magnetics, the most common failure mode is a shorted/leaky cap, and a close second is a shorted/leaky HV rectifier. It can be hard to determine the exact failure using only low-voltage gear, so a 577 curve tracer or equivalent is almost obligatory if a DMM, e.g., doesn't identify the bad component. Substitution is often the way to go if you don't have HV test gear, unless the replacement parts are ridiculously expensive.One note on the cap: Its value matters, as it is chosen to resonate with the leakage inductance of the HV transformer.-- Cheers,Tom-- Prof. Thomas H. LeeAllen Ctr., Rm. 205350 Jane Stanford WayStanford UniversityStanford, CA 94305-4070 12/12/2021 15:05, Jim Ford wrote:> Hi, everybody.? Has anybody else seen this issue: one day recently, > out of the blue, our Kitchen Aid microwave oven stopped working. One > day it was fine, and the next day the display was blank, and the > keypad wouldn't respond to anything.? So I attempted to open it up, > thinking a catastrophic fault like this might be easy to fix.? I had > to go to Home Depot to get a set of those Torx drivers with the hole > in the center because the screws holding the cover on are Torx with > the pin in the center.? Not that I mind buying a new tool, of course!? > So I opened it up yesterday, and sure enough, the 20 amp fuse was > blown.? Really, really blown - the metal inside was splattered all > over the glass!>> I checked YouTube, watched a few videos, and decided to discharge and > measure the high voltage capacitor, a known weak point.? So I grabbed > some alligator clips, some banana leads, and a 2 ohm, 25 W wirewound > resistor I had lying around.? I didn't think discharging the cap, a > 0.95 uF job, with a dead short was a good idea.? The cap measured > about 130 ohms and 0.00 V, but the ohms reading was very unstable.? I > realized the HV transformer was still in the circuit, so I > disconnected the cap leads (very hard to get the clips off, BTW) and > measured again.? Megohms this time and about 0.2 V (I chalked that up > to dielectric absorption).>> I figured it wasn't the cap, and maybe the original fuse was faulty or > a power surge had fried it.? I hoped for the best and made another > trip to Home Depot and bought a ceramic fuse. Actually 2 in a pack.? > Put one in the microwave oven and was pleased to hear it beep and get > all zeros on the display.? Short lived, though, because the kitchen > lights dimmed, and the display went blank.? Sure enough, the fuse was > open now.>> So, anybody have an idea what to check next?? Or is the cap indeed > blown and in need of replacement?? I'd sure hate to have to trash this > appliance after only about 4 years (1 year warranty, of course!).? And > I'd hate even more to have to spring for another one.? IIRC, it was > about $750 new.>> Thanks.>> Jim Ford in Southern California, USA>>> >>
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Value on the HV cap is 0.95 uF +/- 3%.? Now I know the reason for that.? Thanks, Tom.? ? ? ? ?JimSent from my Verizon, Samsung Galaxy smartphone
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-------- Original message --------From: Tom Lee <tomlee@...> Date: 12/12/21 5:26 PM (GMT-08:00) To: [email protected], [email protected] Subject: Re: [TekScopes] OT: microwave oven blows fuse Hi Jim,I haven't fixed nearly as many microwaves as scopes, but more than a handful. For ovens using a traditional power supply with line-frequency magnetics, the most common failure mode is a shorted/leaky cap, and a close second is a shorted/leaky HV rectifier. It can be hard to determine the exact failure using only low-voltage gear, so a 577 curve tracer or equivalent is almost obligatory if a DMM, e.g., doesn't identify the bad component. Substitution is often the way to go if you don't have HV test gear, unless the replacement parts are ridiculously expensive.One note on the cap: Its value matters, as it is chosen to resonate with the leakage inductance of the HV transformer.-- Cheers,Tom-- Prof. Thomas H. LeeAllen Ctr., Rm. 205350 Jane Stanford WayStanford UniversityStanford, CA 94305-4070 12/12/2021 15:05, Jim Ford wrote:> Hi, everybody.? Has anybody else seen this issue: one day recently, > out of the blue, our Kitchen Aid microwave oven stopped working. One > day it was fine, and the next day the display was blank, and the > keypad wouldn't respond to anything.? So I attempted to open it up, > thinking a catastrophic fault like this might be easy to fix.? I had > to go to Home Depot to get a set of those Torx drivers with the hole > in the center because the screws holding the cover on are Torx with > the pin in the center.? Not that I mind buying a new tool, of course!? > So I opened it up yesterday, and sure enough, the 20 amp fuse was > blown.? Really, really blown - the metal inside was splattered all > over the glass!>> I checked YouTube, watched a few videos, and decided to discharge and > measure the high voltage capacitor, a known weak point.? So I grabbed > some alligator clips, some banana leads, and a 2 ohm, 25 W wirewound > resistor I had lying around.? I didn't think discharging the cap, a > 0.95 uF job, with a dead short was a good idea.? The cap measured > about 130 ohms and 0.00 V, but the ohms reading was very unstable.? I > realized the HV transformer was still in the circuit, so I > disconnected the cap leads (very hard to get the clips off, BTW) and > measured again.? Megohms this time and about 0.2 V (I chalked that up > to dielectric absorption).>> I figured it wasn't the cap, and maybe the original fuse was faulty or > a power surge had fried it.? I hoped for the best and made another > trip to Home Depot and bought a ceramic fuse. Actually 2 in a pack.? > Put one in the microwave oven and was pleased to hear it beep and get > all zeros on the display.? Short lived, though, because the kitchen > lights dimmed, and the display went blank.? Sure enough, the fuse was > open now.>> So, anybody have an idea what to check next?? Or is the cap indeed > blown and in need of replacement?? I'd sure hate to have to trash this > appliance after only about 4 years (1 year warranty, of course!).? And > I'd hate even more to have to spring for another one.? IIRC, it was > about $750 new.>> Thanks.>> Jim Ford in Southern California, USA>>> >>
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Check the interlock switches.
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Glenn On 12/12/2021 6:05 PM, Jim Ford wrote:
Hi, everybody.? Has anybody else seen this issue: one day recently, out of the blue, our Kitchen Aid microwave oven stopped working. One day it was fine, and the next day the display was blank, and the keypad wouldn't respond to anything.? So I attempted to open it up, thinking a catastrophic fault like this might be easy to fix.? I had to go to Home Depot to get a set of those Torx drivers with the hole in the center because the screws holding the cover on are Torx with the pin in the center.? Not that I mind buying a new tool, of course!? So I opened it up yesterday, and sure enough, the 20 amp fuse was blown.? Really, really blown - the metal inside was splattered all over the glass! --
----------------------------------------------------------------------- Glenn Little ARRL Technical Specialist QCWA LM 28417 Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178 QTH: Goose Creek, SC USA (EM92xx) USSVI, FRA, NRA-LM ARRL TAPR "It is not the class of license that the Amateur holds but the class of the Amateur that holds the license" |
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Don Bitters
I have minor knowledge of Microwave ovens, but you have a large current draw when it fails, to dim your kitchen lights and blow a 20amp ceramic fuse (those tend to be slow blow), and you did nothing to turn the microwave tube on (not from the description you gave). So starting from the plug, check the resistance to ground from the high and low sides. If resistance checking doesn¡¯t get you anywhere then check the coloration of any capacitors, resistors, IC¡¯s, etc. I might disconnect the microwave tube and repeat the power up check.
On another note, your microwave issues should not dim your lights, they should be on separate circuits (lighting on 15 amp breakers, 14 ga. wiring, outlets on 20 amp breakers, 12 ga. wiring) You may also have a problem purchasing repair parts, you may have to show certification in microwave oven repair to buy parts, unless they are generic parts. Don Bitters |
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Hello Jim,
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There is one other possibility that has not been mentioned in this OT discussion thus far and that is the very basic protection mechanism implemented by a combination of limit switches in the door interlocks. It is designed to blow the fuse should the door interlock NOT function correctly. You will almost certainly require the schematics for your particular microwave oven to facilitate debugging this unless you are able to easily access said limit switches inside the door interlock assemblies. There should be 3 of those micro-switches and, as you slowly open the door, you should never measure a short-circuit across the 240VAC supply when measured from the feed side to the transformer (of course, with the latter disconnected. I hope this helps should you have exhausted all other possibilities (bad resonant cap, bad diode, shorted transformer or bad magnetron). I had both of our microwave ovens fail in this precise manner in the last 6 months. These micro switches take a fair beating over the years, especially if you have teenagers in the house ? Cheers, Rick Melbourne, AUSTRALIA On 13 Dec 2021, at 12:05, Jim Ford <james.ford@...> wrote: |
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On Mon, Dec 13, 2021 at 06:13 AM, momemeca wrote:
...very basic protection mechanism implemented by a combination of limit switches in the door interlocks.This is explained in this service information... just one picked at random, as I got interested although my microwave works. cheers Martin |
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I don¡¯t like ¡°shotgun¡± repairs, but have you tested the HV diode yet?
In the old microwave ovens with the heavy iron transformer, this was the usual failure mode. But usually the diode failed open; in your case it may have shorted. OTOH if you have a switcher HV supply, you may need to put that microwave out at the curb. And that may be a harbinger of things to come ¡ª microwaves with GE-style programmed self-destruction. In any case, it makes our 46-year-old Kenmore worth repairing, and our early 70s Amanda Radar Range worth running until we die, or at least until the ¡®58 Cadillac style chrome falls off. 73 Jim N6OTQ Sent from my quenched-gap spark transmitter. |
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On Sun, Dec 12, 2021 at 07:26 PM, Tom Lee wrote:
One note on the cap: Its value matters, as it is chosen to resonate with the leakage inductance of the HV transformer.Really? I've never heard this before. So they are expected to "ring" to give higher voltage than would otherwise be expected? That seems like it would be hard to control, even with a +/- 3% capacitor. |
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John Griessen
On 12/13/21 06:22, Jim Strohm wrote:
In any case, it makes our 46-year-old Kenmore worth repairing, and our early 70s Amanda Radar Range worth running until we die, or at least until the ¡®58 Cadillac style chrome falls off.I've operated 70's 80's Radaranges too! The power is low now as the magnetron tubes aged. I'm thinking of adding new DC driven 250 Watt oscillator modules and taking the old transformer and magnetron out just to have the nice chrome... But wait, is that the element mentioned as planned self destruct? |
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Just a note on dealing with HV diode failure. (I don't have a curve tracer).
Years ago I had access to defective Laptop Lithium Ion battery packs. They usually failed with one 18650 cell going bad and several good cells in fine shape. I rescued and collected the good cells and found they could be charged and stacked nicely in a PVC tube contraption I made, utilizing a spring to maintain terminal contact. This was handy when checking the HV diodes (I'd usually test around 200VDC), just stacking enough 4+VDC cells in the PVC tube for the desired voltage. I have fixed a few microwaves by replacing the HV diodes which can be obtained on Ebay quite reasonably. On the newer microwaves, if you are looking at a failed inverter, forget it (unless you want to debug the inverter), it fails often and is expensive to replace. |
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On Mon, Dec 13, 2021 at 06:57 AM, Jim Adney wrote:
The magnetron wants roughly double the output of the transformer. (Cheap transformer here is the idea... to keep the cost of the transformer as low as possible...for the commodity domestic microwave oven market.)Really? I've never heard this before. So they are expected to "ring" to give And so...oven designers use a Villard doubler... designed/discovered by the same guy that discovered gamma rays! ... instead of a more expensive higher voltage transformer. If you want to drive a square peg into a round hole... which I'm gonna do... you can look at the Villard doubler... as used in those old, 'big iron' transformer sporting ovens.. the ones with a lot of gravity... you can look at the Villard doubler in them... as 'like' a poor man's (poorly designed)... fixed frequency series resonant DC to DC converter. (Remember, I stipulated 'like.') The goal is with a relatively s**t transformer... to try to get resonance at the fixed fixed frequency of operation... because that's where you would get maximum current... but, I'd say (because I haven't measured it) that's seldom the case. (These ovens are designed to maximise cheapness... not precision.) Just the same with given transformer, and diode, and an arbitrary capacitance value... whose effect is to significantly 'detune' the circuit... well you won't get maximum current... and if you are too far off.... you won't get the rated power of the oven. -- Roy Thistle |
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Hi Jim,
My microwave stopped working. I don't recall if it finally blew the fuse, but it was arcing behind the control panel. Being an electrical engineering, I investigated the circuit as you and other have suggested. Nothing seemed to be amiss. It turned out that the little microwave transparent window in the back upper right of the unit had food splashed on it. The dirty window was not allowing the microwave energy to get into the enclosure. As a result the energy found another path and caused the arcing. A $4 replacement window from Amazon solved the problem. Dave PS, my wife wanted to just throw it out and buy a new one, but like many here, the reward of fixing something outweighs the financial consideration of the time spent on the repair. |
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Thanks, Dave (and all the others who have given recommendations).? I poked around a bit, and all the door switches operate properly, the relays are all open circuited as shown on the wiring diagram, and nothing seems amiss.? The only thing that's weird is a bit of rust in one corner on the screws holding the main cover and the cover over the convection fan, like water was sitting on there for a while.? Last night I put in a cheapie glass fuse and turned it on, expecting it to blow right away.? Nope, and it even heated up a mug of water.? Of course then I stripped a sheet metal screw hole, the one right under the magnetron!? Any other screw hole I would have left alone.? So I found a nut that would fit and epoxied it in place.? Tonight I will put it all back together and hope there was just a temporary short somewhere that was blowing fuses.? ?Otherwise it's back to the drawing board.....? ? ? ? ?JimSent from my Verizon, Samsung Galaxy smartphone
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-------- Original message --------From: ebayatessnh <ebay@...> Date: 12/17/21 6:30 AM (GMT-08:00) To: [email protected] Subject: Re: [TekScopes] OT: microwave oven blows fuse Hi Jim,My microwave stopped working. I don't recall if it finally blew the fuse, but it was arcing behind the control panel. Being an electrical engineering, I investigated the circuit as you and other have suggested. Nothing seemed to be amiss.It turned out that the little microwave transparent window in the back upper right of the unit had food splashed on it. The dirty window was not allowing the microwave energy to get into the enclosure. As a result the energy found another path and caused the arcing.A $4 replacement window from Amazon solved the problem.DavePS, my wife wanted to just throw it out and buy a new one, but like many here, the reward of fixing something outweighs the financial consideration of the time spent on the repair.
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Hello everyone, I have been reading on this board and not knowing the answers till I got to this post. I have been repairing commercial food equipment for 20 plus years and microwaves are part of that. What is going on here is the door interlock switch is worn out, the hook on the door latch has worn the plastic in the interlock switch and messed up the timing of the limit switches. The door interlock has three switches, primary, secondary, and the monitor. As the door opens, both primary and secondary must open before the Monitor closes. Primary and secondary are in both legs of power supplied to high voltage transformer, in this case hot and neutral. Monitor is across both legs, again hot and neutral in this case. This causes a dead short and blows the main fuse if either primary or secondary interlock switch is not open before the Monitor closes. Primary and secondary are normally open and monitor is normally closed. If the HV transformer burns and causes high current draw this usually blows the breaker for the outlet and leaves fuse in microwave fine. The reason for this is to prevent opening the door with magnetron putting out microwaves and cooking the person that opens the door or pacemaker interference. If we run into a unit that has a blown main fuse we automatically replace the door interlock switch, don't pass go just do it. The door hook slamming into the plastic of the interlock switch wears the plastic where it eventuality makes the primary and secondary not open fast enough before monitor closes and blows the extremely fast blow fuse preventing relay or limit switch contacts from welding closed. You need a new interlock switch and fuse.
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Thank you very much, Ben. That squares with the information provided by some other contributor. I'd never studied the complete logic of how the safety interlocks worked. Good to know that there exists a failure mode that can pop the fuse, yet doesn't involve the power supplies.
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-- Cheers, Tom -- Prof. Thomas H. Lee Allen Ctr., Rm. 205 350 Jane Stanford Way Stanford University Stanford, CA 94305-4070 On 12/17/2021 19:15, benwetzel via groups.io wrote:
Hello everyone, I have been reading on this board and not knowing the answers till I got to this post. I have been repairing commercial food equipment for 20 plus years and microwaves are part of that. What is going on here is the door interlock switch is worn out, the hook on the door latch has worn the plastic in the interlock switch and messed up the timing of the limit switches. The door interlock has three switches, primary, secondary, and the monitor. As the door opens, both primary and secondary must open before the Monitor closes. Primary and secondary are in both legs of power supplied to high voltage transformer, in this case hot and neutral. Monitor is across both legs, again hot and neutral in this case. This causes a dead short and blows the main fuse if either primary or secondary interlock switch is not open before the Monitor closes. Primary and secondary are normally open and monitor is normally closed. If the HV transformer burns and causes high current draw this usually blows the breaker for the outlet and leaves fuse in microwave fine. The reason for this is to prevent opening the door with magnetron putting out microwaves and cooking the person that opens the door or pacemaker interference. If we run into a unit that has a blown main fuse we automatically replace the door interlock switch, don't pass go just do it. The door hook slamming into the plastic of the interlock switch wears the plastic where it eventuality makes the primary and secondary not open fast enough before monitor closes and blows the extremely fast blow fuse preventing relay or limit switch contacts from welding closed. You need a new interlock switch and fuse. |
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Crap!? I read this after I got it all put back together and seems to be working!? So, Ben, I need to replace which switch?? The top and bottom switches are indeed NC, and the monitor switch in the middle is NO.? Thanks.? ? ? ? ?JimSent from my Verizon, Samsung Galaxy smartphone
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-------- Original message --------From: "benwetzel via groups.io" <benwetzel@...> Date: 12/17/21 7:15 PM (GMT-08:00) To: [email protected] Subject: Re: [TekScopes] OT: microwave oven blows fuse Hello everyone, I have been reading on this board and not knowing the answers till I got to this post.? I have been repairing commercial food equipment for 20 plus years and microwaves are part of that.? What is going on here is the door interlock switch is worn out, the hook on the door latch has worn the plastic in the interlock switch and messed up the timing of the limit switches.? The door interlock has three switches, primary, secondary, and the monitor.? As the door opens, both primary and secondary must open before the Monitor closes.? Primary and secondary are in both legs of power supplied to high voltage transformer, in this case hot and neutral.? Monitor is across both legs, again hot and neutral in this case.? This causes a dead short and blows the main fuse if either primary or secondary interlock switch is not open before the Monitor closes.? Primary and secondary are normally open and monitor is normally closed.? If the HV transformer burns and causes high current draw this usually blows the breaker for the outlet and leaves fuse in microwave fine.? The reason for this is to prevent opening the door with magnetron putting out microwaves and cooking the person that opens the door or pacemaker interference.? If we run into a unit that has a blown main fuse we automatically replace the door interlock switch, don't pass go just do it.? The door hook slamming into the plastic of the interlock switch wears the plastic where it eventuality makes the primary and secondary not open fast enough before monitor closes and blows the extremely fast blow fuse preventing relay or limit switch contacts from welding closed.? You need a new interlock switch and fuse.
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momemeca
Martin
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