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Our 110V Brother sewing machine got plugged into the 220V side of our step down transformer. After a short pop, it does not turn on. I pulled the power supply board out and it seems like just an input fuse was blown along with the black component which I think is a DIAC from the symbol on the board.

The number on what I think is the DIAC is V102210 with ZNR above it.

  • Is the DIAC being used as voltage protector for the machine?
  • Would it be possible to just replace the DIAC with just a jumper? I just wouldn't have any protection next time. I removed the fuse and DIAC from the board.

![enter image description here

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  • \$\begingroup\$ Once you have repaired it properly as per the answer, then you should consider making sure the plugs/sockets for 220V are different to the plugs/sockets for 110V... \$\endgroup\$
    – Solar Mike
    Mar 14, 2018 at 16:59
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    \$\begingroup\$ That looks more like a varistor than a diac. Shouldn't be hard to find a replacement. \$\endgroup\$
    – Finbarr
    Mar 14, 2018 at 17:05
  • \$\begingroup\$ Think you are right about it being a varistor. Basically it just there to blow if the voltage is too high? Now how do I figure out what specifications I need on the one to replace it? \$\endgroup\$
    – Chase W
    Mar 14, 2018 at 17:15
  • \$\begingroup\$ It's there to absorb brief voltage surges and not to blow under normal circumstances. Plugging in double the supply voltage doesn't qualify! \$\endgroup\$
    – Finbarr
    Mar 14, 2018 at 17:18
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    \$\begingroup\$ A varistor doesn't work like a fuse. It goes across the supply, not inline like a fuse does. You should be able to see this from the tracks on the back of the board. \$\endgroup\$
    – Finbarr
    Mar 14, 2018 at 17:28

2 Answers 2

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The component is almost certainly a metal oxide varister. It is designed to absorb voltage surges by shorting them out but it is not designed to take sustained overvoltage. Connecting a MOV chosen for a 120V only application to a 240V supply will almost certainly destroy it.

As to replacing it unfortunately googling the part number printed on the device turned up a blank.

http://www.littelfuse.com/~/media/electronics_technical/application_notes/varistors/littelfuse_selecting_a_littelfuse_varistor_application_note.pdf suggests that for 120V applications you want a MOV with a continuous AC rating of about 140V (to allow for supply voltage tolerances).

Selecting the peak current rating is trickier, personally for a one-off repair I would just go for the highest peak current rating I could get in an acceptable package size.

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  • \$\begingroup\$ That M logo was used by Matsushita, who now trade under the name Panasonic. They may be able to advise the correct replacement from their ZNR range. The 10 at the start usually means a 10mm nominal diameter and the rest is usually related to the voltage. \$\endgroup\$
    – Finbarr
    Mar 14, 2018 at 17:43
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If you've done it once you'll do it again don't just jump the connection assume that you WILL plug it into the 220V again. If your sure that these components are the only problem you should just replace them with new ones or equivalent.

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