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whacked by asploding transformer, part deux

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whacked by asploding transformer, part deux Nate Nagel 05-17-2008
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Posted by Nate Nagel on May 17, 2008, 5:35 pm
Hi all,

finally tore down my dishwasher today after getting sick of doing dishes
by hand and striking out on Craigslist. For those of you that missed
the first installment, a transformer exploded a couple streets over late
Sunday night or early Monday morning and blowed up some stuff in my
house (a surge strip, an electrostatic air filter, and my dishwasher.)
I've already ordered (online) a new power supply for the air filter, and
replaced the surge strip and the TVSS breaker that was in my main panel
(the "protected" light was out on one leg.)

Turns out that the failure of the dishwasher looks exactly like the
failure of the air filter; on the power supply board there is a
orangeish-yellow dsc-shaped component soldered onto the board about 1/2"
in diameter, and it appears to have failed with extreme prejudice. Am I
correct in assuming that this is a MOV? Could I just do a component
level repair of this rather than replace the whole board? I really hate
this dishwasher and don't want to spend a lot of money on it. If this
is a MOV, is value important, or simply "bigger is better?" I'm sorry
for the dumb questions, but I'm not particularly electronically
knowledgeable (made it through two EE classes in college and I think
I've forgotten most of what I learned) just trying to get this back up
and running. If Trible's had still been open by the time I got it
apart, I probably wouldn't be asking the question, but if there's a
chance I could fix it today...

thanks,

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

Posted by Nate Nagel on May 17, 2008, 6:17 pm
Nate Nagel wrote:
> Hi all,
>
> finally tore down my dishwasher today after getting sick of doing dishes
> by hand and striking out on Craigslist. For those of you that missed
> the first installment, a transformer exploded a couple streets over late
> Sunday night or early Monday morning and blowed up some stuff in my
> house (a surge strip, an electrostatic air filter, and my dishwasher.)
> I've already ordered (online) a new power supply for the air filter, and
> replaced the surge strip and the TVSS breaker that was in my main panel
> (the "protected" light was out on one leg.)
>
> Turns out that the failure of the dishwasher looks exactly like the
> failure of the air filter; on the power supply board there is a
> orangeish-yellow dsc-shaped component soldered onto the board about 1/2"
> in diameter, and it appears to have failed with extreme prejudice. Am I
> correct in assuming that this is a MOV? Could I just do a component
> level repair of this rather than replace the whole board? I really hate
> this dishwasher and don't want to spend a lot of money on it. If this
> is a MOV, is value important, or simply "bigger is better?" I'm sorry
> for the dumb questions, but I'm not particularly electronically
> knowledgeable (made it through two EE classes in college and I think
> I've forgotten most of what I learned) just trying to get this back up
> and running. If Trible's had still been open by the time I got it
> apart, I probably wouldn't be asking the question, but if there's a
> chance I could fix it today...
>
> thanks,
>
> nate
>

Never mind... I think I just answered my own question. The MOV, which
I'm pretty sure what I'm looking at, in the dishwasher, shows no
continuity when probed with my trusty Fluke, so that should not prevent
the dishwasher from functioning (but *would* leave it without surge
protection.) So I ASSume that something else is also fried on that board.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

Posted by AZ Nomad on May 17, 2008, 9:17 pm

>Never mind... I think I just answered my own question. The MOV, which
>I'm pretty sure what I'm looking at, in the dishwasher, shows no
>continuity when probed with my trusty Fluke, so that should not prevent

An MOV will never show continuity when measured with a multimeter. The
resistance is nearly infinite until the breakdown voltage is reached,
then it drops to zero. To test an MOV, you need a voltage source greater
than the breakdown voltage, and a series resistor so the MOV won't damage
your power sourcde.

Posted by Dave Martindale on May 18, 2008, 1:50 pm

>Never mind... I think I just answered my own question. The MOV, which
>I'm pretty sure what I'm looking at, in the dishwasher, shows no
>continuity when probed with my trusty Fluke, so that should not prevent
>the dishwasher from functioning (but *would* leave it without surge
>protection.) So I ASSume that something else is also fried on that board.

Check for a blown fuse. Sometimes the MOV is downstream from a fuse,
with the intent that the MOV will absorb small surges, and blow the fuse
on large surges that the MOV cannot absorb. If you're lucky, replacing
the fuse might have it running again.

But more likely something else is fried. If the MOV is the only thing
destroyed, the rest of the circuit would work, and you could just
replace the MOV at your leisure. The fact that the circuit doesn't work
suggests that the overvoltage was too much for the MOV and it probably
took out one or more other voltage-sensitive devices too.

        Dave


Posted by Joseph Meehan on May 17, 2008, 6:50 pm
> Hi all,
>
> For those of you that missed the first installment, a transformer
> exploded a couple streets over late Sunday night...
>
> Turns out that the failure of the dishwasher looks exactly like ... >
> thanks,
>
> nate
>
> --
> replace "roosters" with "cox" to reply.
> http://members.cox.net/njnagel


Why are you doing this? If it was due to a utility company transformer
defect, don't they pay? If not don't you have homeowner's insurance that
covers it?


--
Joseph Meehan

Dia 's Muire duit




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