• ** REMEMBER! **The microwave can still shock you even unplugged!!

    ALWAYS discharge the high-voltage capacitor first if you even think your hands will come close to any HIGH VOLTAGE components.

    Jeff mentions this: Anything in the high voltage ( magnetron, capacitor, diode, wires to and from ):
    ...Use a metal ( not the shiny chrome type ) screw driver with a insulated handle to short across ( touch both at the same time ) the terminals of the high voltage capacitor to discharge it.

    From Jeff's site: http://www.applianceaid.com/component-testing.php

    Jake
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FIXED Bosch Microwave HMV3053U/01 Tripping Breaker

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wpollock

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Location
California
Model Number
HMV3053U/01
Brand
Bosch
Age
1-5 years
Started off throwing breaker every time door was closed but now has progressed to not being able to reset breaker if unit is plugged in to dedicated outlet. Checked outlet and breaker to be good by plugging a hair dryer and running with no issues. Removed microwave since it was secured to exhaust vent by aluminum tape. Here are a few pictures showing position of door switches. Middle switch is closely stacked on top of bottom switch. Do I need to remove the door bracket holding the switches to test them?
IMG_20211005_175340.jpg
IMG_20211005_175527.jpg
 

rickgburton

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Remove the wires from the switches and check them for continuity by opening and closing the door.
 

wpollock

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All three of the switches in my unit are two terminal. Provided all the switches are good, is it common on all microwaves for the top (Primary) switch to have continuity when the door is open, the middle (Monitor) switch to have continuity when the door is closed and the bottom (Door Sensor) switch to have continuity when closed?
 

rickgburton

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I don't have any information on that model. I would need a wiring diagram to tell you if the switch is Normally Open or Normally Closed. You can tell by looking at the switch. Most interlock switches are both NO and NC. Each switch has a C (common) terminal and a NO terminal and a NC terminal. On a two wire switch one of the terminals is not used or missing. If the wires are on the C and NO terminals, it's a Normally Open switch which means with the door open the switch is open. With the door closed the switch is closed.
Microswitches.jpg
 

wpollock

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Tested all switches in place and the middle switch tested bad. Removed the switch door bracket and with the switch still in place the actuator tab would not click as would the tabs on the top and bottom switches. Removed the switch and after a few times depressing and releasing the tab it started clicking again. The switch now tests to be good. Pictures to ask if I am correct in saying it is a Normally closed switch?
 

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rickgburton

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The switch now tests to be good. Pictures to ask if I am correct in saying it is a Normally closed switch?
Don't reuse it. That's the monitor switch, a normally closed switch. Sometimes called the deadman switch, when the door is open L1 is shorted to Neutral (a dead short). It's designed so there's no way the high side components can be energized with the door open.
 

wpollock

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The gray switch nomenclature matches exactly with what is on the defective switch in the microwave. The black switch is the closest match at my local Grainger Supply. It is easily accessible, available for immediate pick up and is less expensive as well. There is a slight difference in the VAC amperage rating between the two so I would like to ask if I would do any damage to the microwave using the Grainger (black) switch as a replacement.
 

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rickgburton

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It should work OK. One of the differences between switches is the amount of pressure it takes on the button to activate the switch.
 

wpollock

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Installed replacement middle ( door monitoring ) switch and unit is operating normally. The question is, for how long? This specific make and model microwave is installed by all builders in my development as part of the builder appliance package. The oldest homes are going on four years and problems, including the door switches, with this microwave started presenting as early as 10 months from installation. It is my humble opinion that there is a manufacturer's defect but will never be admitted to.
Thanks for all the help
 

Jake

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rickgburton

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Looks like it:
 

Jake

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Thanks Rick!

Jake
 

Seaduner

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My model HMV3053U/01 would blow the 20A fuse insider the microwave, it didn't trip the house breaker, likely because the house breaker is 20A breaker for our microwave.

As mentioned, a bad door switch can blow the fuse. My situation was intermittent, got worse with time. The first time I blew a fuse I replaced it. However, the oven worked for about a week, then it blew fuse blew again. This time the replacement fuse blew right away without turning on the oven, by just plugging the oven into power. The fuse blew immediately (with the door shut), so I dug into the problem.

When I tested my switches, they all tested good. Fortunately I found a test diagram that Bosch provided, folded up and stuffed in a crevasse in the plastic keypad eschaton when I removed it. That diagram shows which switches are normally on, and normally off, as the door is opened and closed. That diagram was very helpful to understand what's going on. When testing the switches worked properly when opening and closing the door. As it turns out they were marginally bad, and I think I know the cause, explained below.

After all switches tested good (while switches were in the holding bracket), I put things back together to test it again with a new fuse. This time I opened the door and plugged the oven into power. I waited a minute, the fuse didn't blow, which was different than before when it immediately blew when plugged into power (door closed). When I closed the door, surprisingly the fuse didn't blow. Yes, I was puzzled. So I kept opening and closing the door and about the 15th time the fuse finally blew.

I proceeded to take each of the 3 switches out, because I knew something was marginally wrong with the switches, given the evidence of opening and closing the door eventually made the fuse blow. Upon closer observation during the continuity testing, I noticed when each switch has a slight delay in the continuity action. When opening and closing the switches, they were not instantly open and closed with the trigger button. There was a slight 100 to 200ms delay, clearly noticeable by the eye. This means the timing of all switches are not in sink. Switches should conduct, or be open immediately. If the timing varies 100ms, that slight delay could short the monitor switch to ground, as mentioned by @rickgburton, enough to blow the fuse. Why are the switch latencies poor? There appears to be a lot of arcing going on inside the switch, maybe too much power for the switch capability to handle the power. Bosch may have used a switch that isn't capable of switching that much power, reliably, for many years. I believe that over time the switch gets so worn from the constant arcing with each contact, that the switch starts to weld the contacts together from heat. In the beginning the switch could be sticking slightly which slows down the switch contact latency. Bottom line, after 3yrs you can expect the switches to be unreliable IMO. I recommend replacing all switches, because when I took them apart they all showed signs of arcing and soot inside the switch, like shown below.

These switches are dependent on the little copper colored spring (looks like a bow) to hold the contacts in place, on or off. So any arcing could potentially weld the contact, and the spring isn't strong enough to pull the contacts apart, quickly. The evidence I saw proves it's a poor design, IMO. $33.66 for the 3 switches from AppliancePartsPros and it's fixed. Those guys ship fast!
 

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rickgburton

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opening and closing the door eventually made the fuse blow.
the timing of all switches are not in sink.
believe that over time the switch gets so worn from the constant arcing
Close. There is no arching in the monitor switch when it opens or closes. Any arch will blow the fuse because no voltage can flow thru it. One wire is neutral and the other wire is L1 and with the switch contacts closed (door open) it's a dead short. The interlock switches do wear out but it's not as common as you think. This part is responsible for more monitor switch failures than anything else. The latch wears out more often than the switches
bosch-lock-648909-ap4513044_03_l.jpg
 

Seaduner

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There is no arching in the monitor switch when it opens or closes
All 3 switches showed evidence of conducting a lot of amps when I opened up the guts of each switch. You may think no current flows there, but the evidence shows otherwise. The connector terminals are discolored from heat, and inside the switch they all showed soot/carbon and significant contact erosion, evidently from sparking/arcing when making contact. The photo I provided of the inside of the switch clearly show that evidence (click photo for an expanded view). You won't get that kind of wear, soot, and discoloration without significant sparks and arcs from too many amps. I still believe Bosch used subpar switches for the power that's being handled. They're clearly marginal, and prone to failure. My last Bosch microwave I owned in this house lasted 12 years. This one is only 3yrs old. I won't be buying Bosch anymore, given the evidence. They used to be a good brand.

I find the switch continuity latency when triggered a bit strange. New switches don't have such continuity latency when triggered. I'm wondering if the heat generated from an overworked switch weakens the trigger spring inside, producing a latency that ruins the timing of all 3 switches being triggered simultaneously.
 

rickgburton

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I never mentioned the primary interlock or the secondary interlock. There very well might be signs of arcing inside both and that's normal. Current flowing thru those switches will definitely arch when the contacts open and over time you'll see signs of that in the switch and on the contacts. But it's such a little spark.....LOL. I was referring to the switch in your picture, the monitor switch I believe.
You may think no current flows there, but the evidence shows otherwise.
I know for a fact there's no current flow through the monitor interlock. It would be literally impossible.
You won't get that kind of wear, soot, and discoloration without significant sparks and arcs from too many amps.
You're absolutely 100% correct. But not over time, all at once. Significant sparks? You betcha. Too many amps? At least 20! If you want to know what went on inside that switch, take an old lamp cord, strip the ends, plug it in and touch the two ends together.

The point I was trying to make was the 14 times you opened and closed the door, the primary interlock used that "1ms" delay to cut the power to the monitor switch before the contacts could close. On the 15th try the monitor switch contacts closed before power was interrupted. More times than not, the problem isn't a sticky primary or secondary interlock but a worn switch holder/latch assy.
 

Seaduner

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More times than not, the problem isn't a sticky primary or secondary interlock but a worn switch holder/latch assy
So you're saying the black plastic bracket that holds the 3 switches can be worn? I can't imagine how a bracket that's fairly beefy, and no moving parts can be worn, unless it's heated to a point to warp somehow, which I can't perceive occurring. Have you experienced that bracket getting warped somehow?
I still think the slow latency I saw on the continuity I saw when test triggering each switch has something to do with the root problem of the timing tolerance of all 3 switches working simultaneously.
 

rickgburton

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So you're saying the black plastic bracket that holds the 3 switches can be worn?
That's what I'm saying
Have you experienced that bracket getting warped somehow?
Hmm.. probably but not to where it was noticeable. I'm sure the high heat environment above the range over time could cause it to warp. Some machines have a small amount of adjustment in the switch bracket. Not all latch assemblies look the same or work the same and some have a lot of moving parts. You're overthinking it. When I check the interlocks by opening and closing the door, they're either good (0) or bad (1).
I still think the slow latency I saw on the continuity I saw when test triggering each switch has something to do with the root problem of the timing tolerance of all 3 switches working simultaneously.
Yes, but who cares? You're looking at it from an engineers point of view and not a repair point of view. If the monitor interlock causes the fuse to blow either the switch is bad (contacts stuck) or the primary interlock is bad (sticky) or the switch holder is bad (worn).
 

Seaduner

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When I check the interlocks by opening and closing the door, they're either good (0) or bad (1).
This differs from my situation, which tested good, but are bad. When replaced the fuse the first time the oven worked for a week, then blew again. That means the switches weren't totally bad, and they individually tested good for continuity. The anomaly is the latency I mentioned, that seemed to be consistent, but I had no way to measure the continuity latency to be sure. Then after I tested each switch as good, the fuse didn't blow until about the 15th door open/close cycle, just opening and closing the door (no microwave cooking). So the switches worked OK for 14 open/close cycles, and finally something went awry on the 15th and blew the fuse. So I believe there's a condition where a switch is marginal, and occasionally sticks the contacts, or the continuity latency is too slow when activating the switch button. Since all switches showed signs of contact wear when I opened them up, and having lots of soot/carbon, I replaced all 3 while I had it apart. Do you agree replacing all of them is prudent? So IMO testing the switches for viability in this situation isn't always a viable diagnosis. You just have to know that those switches go bad and replace all of them, then hope it stops blowing the fuse. If not, then consider wear as you mentioned, or bracket warp that throws of the timing of all switches working in sync.

UPDATE: I misspoke before, only the two black switches showed extreme pitting and wear on the switch contacts. These are the monitor switch and primary switch. Those were badly worn. I just open up the gray "door sensing switch", which is the bottom switch (and most expensive at $11) Inside that switch the contacts had practically no wear, no signs of arcing and soot like the other two. However one of the terminals was slightly discolored, possibly from heat.

Do you know if the switches are specifically designed to have a ~100ms continuity latency, to help with the timing tolerances?
 
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