Author Topic: Micro. no power after bulb put in and spark's flew  (Read 1074 times)

Offline rego

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Micro. no power after bulb put in and spark's flew
« on: February 11, 2013, 03:07:46 PM »
Model: MWV4205BA   Serial: 16324868NP
Customer was putting in a new bulb underneath and sparks flew and now no display to the microwave.  Fuses are good but no tech sheet and really don't want to go wire by wire and guess what's what so does anyone happen to have a tech sheet/wiring diagram for this model or suggestions.
Thank you as always for your help.

Offline scrapiron

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Re: Micro. no power after bulb put in and spark's flew
« Reply #1 on: February 11, 2013, 03:36:16 PM »
I'm not having any luck with that model #. My best guess is that the surface lights are switched thru the control board. most likely that the glass in the bulb twisted in the base causing a short, taking out the control board. I've seen it happen. take the board out & look at the back side where the solder connections are. You'll most likely see a burned spot. Probably needs a new control.  :(

Offline rego

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Re: Micro. no power after bulb put in and spark's flew
« Reply #2 on: February 11, 2013, 03:45:13 PM »
Sort of what I thought...I'm wondering which one got hit.  There is the small one (inexpensive) which I think is the newer way of stepping up the voltage (has the low and high V fuse on it) and the main board at the consol (expensive).  Would you guess the expensive one?  I have power to the smaller step up board that appears in and out.  Power at each side of fuse but not through the fuses...hoping it's the inexpensive one.
I'm not great with microwaves...only see one every six months or so with new ones priced the way they are not worth repair a lot of times.
Thanks!

Offline haroldsappliance

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Re: Micro. no power after bulb put in and spark's flew
« Reply #3 on: February 11, 2013, 03:51:43 PM »
Bad md # what brand is it?

Offline rego

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Re: Micro. no power after bulb put in and spark's flew
« Reply #4 on: February 11, 2013, 03:57:03 PM »
It's a Maytag...I've been having problems finding diagrams too.  I've been crossreferencing between sites.  I have the service manual for it but no wiring diagram and it's not much help...

Offline haroldsappliance

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Re: Micro. no power after bulb put in and spark's flew
« Reply #5 on: February 11, 2013, 04:02:12 PM »
Do u have a correct md#?

Offline rego

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Re: Micro. no power after bulb put in and spark's flew
« Reply #6 on: February 11, 2013, 04:05:11 PM »
I will double check it...

Offline rego

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Re: Micro. no power after bulb put in and spark's flew
« Reply #7 on: February 11, 2013, 04:14:16 PM »
Woops, very wrong...sorry
Model: MMV4205BAS

Offline haroldsappliance

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Re: Micro. no power after bulb put in and spark's flew
« Reply #8 on: February 11, 2013, 04:37:46 PM »
There may be a limit switch such as what's on the ge microwave that is in either the line or nuetral circuit that will,when blown, open circuit to everything including control board. I know that this limit switch is heat sensitive. As to whether it's current sensitive, I'm not sure. I could not find a diagram, maybe AJ has something. Check your fuses and all your limit links that are in either the line or nuetral circuit.

Offline rego

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Re: Micro. no power after bulb put in and spark's flew
« Reply #9 on: February 11, 2013, 04:44:48 PM »
Thanks, good info on tracking...  The fuses are good and only have one open 2 limits on the base behind control panel...one closed one open am assuming the one open is for fan and will close at higher temp. 

Offline domain

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Re: Micro. no power after bulb put in and spark's flew
« Reply #10 on: February 11, 2013, 04:50:08 PM »
Small pcb is your line noise filter that is also fused. Check for 120vac in and 120vac out. If you have 120 vac out, your filter pcb is good. If 120vac is at your main pcb, and control is dead, there lies your problem. You have 3 thermal fuses on this unit unless I'm mistaken. One is for magnatron (Normally closed). One is for oven cavity (Normally closed). The last should be for the stove top (Normally Open). Hope this helps. :D

Offline Bailey

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Re: Micro. no power after bulb put in and spark's flew
« Reply #11 on: February 12, 2013, 10:15:00 AM »
On some microwaves the wiring diagram is behind the grill.

 

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