whacked by asploding transformer, part deux

[Nate Nagel]

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

[Nate Nagel]

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

[Joseph Meehan]

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?

[Jim Yanik]

"Ralph Mowery" wrote in news:k7udnQ3qHawRwbLVnZ2dnUVZ [e-mail]:

Usually,there is a fuse inbetween the MOV and line source,so the fuse opens whne the MOV shunts the surge/spike to ground. I've seen MOVs split open,and PCB traces vaporize,and the power supply still work when the fuse was replaced and trace repaired. Sometimes the switcher transistor/FET gets blown,too.

MOVs usually are marked 130Vxx or 250Vxx,yours probably is a 130V MOV,and they come in varying current sizes.

[Nate Nagel]

'cause I want my stuff back up and running. Apparently there are SO many claims in my area that SWMBO hasn't even been contacted by the power people yet. The insurance company is holding off until they find out whether or not the power company is paying, and they said that they too have been hit by a large number of claims in my area - they're using a "catastrophe team" to deal with all the claims apparently. Which makes me wonder what would happen in a REAL catastrophe - a couple appliances down is a PITA, not the end of the world.

Besides, I figure if I spend a couple minutes figuring out exactly which component got whacked and claim for just that, I'll be more likely to a) get the claim paid and b) if it goes through insurance, not have a rate increase.

nate

[Ralph Mowery]

If it is the MOV, you can just cut it out of the circuit and try the washer. The mov is basically an open circuit and shorts out when a voltage higher than what it is rated for hits it, then opens back up when the voltage returns to normal. This is to protect the circuit board from voltage surges. If they get hit with too big of a surge they may blow off the board.

If the washer works, feel free to use it, but replace the mov as soon as possiable incase you get another surge. You may want to unplug it or cut off the circuit breaker when it is not in use, especially if a storm is near.

The bigger is beter is still in effect. Keep the voltage rating the same, but you can go up in the power rating.

[ransley]

e quoted text -

Insurance companies usualy dont, and shouldnt, work that way, they pay you, then collect from the utility co, thats why you paid them in the first place.

[HeyBub]

It could be a ceramic disk capacitor.

Does it SAY anything on the component ("MOV" would be a clue, so would ".01 mfd")

[AZ Nomad]

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.

[Nate Nagel]

If it does, I can't read it under the blackenedness :)

SWMBO was told by the power company not to throw anything out for claims purposes so if I'm not sure what it is I'm not cleaning/messing with it...

nate

[Bob F]

I would never expect the power company to contact you. If they don't, maybe you won't think to make a claim.

[Nate Nagel]

You misunderstand, probably because I wasn't perfectly clear. She called Tuesday and explained the situation and inquired about making a claim. Left info, etc. and I know they're processing it because we got a letter in the mail today to that effect, but no other communication.

nate

[Edwin Pawlowski]

So just get if fixed and keep the old component as well as the bill for repair. No need to wait around for approval. It is probably below the threshold of you deductible anyway so forget the insurance.

[Dave Martindale]

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