I have a USB Tester like this one:


I have connected it by mistake to a 23 volt power source and the item stopped working. When I opened the item I found that a component was burnt (See the picture below the item marked by the red square): 2

I found a picture of the same board with the component clearly marked V2MJ (See the picture below): 3

I've searched the internet and I couldn't find what is this component. Can anyone help me identify this component and if there is a replacement for it?

P.S. The board is marked with a KCX-017-20131222 marking: 4


closed as off-topic by Nick Alexeev Jun 5 '17 at 13:56

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the repair of consumer electronics, appliances, or other devices must involve specific troubleshooting steps and demonstrate a good understanding of the underlying design of the device being repaired. See also: Is asking on how to fix a faulty circuit on topic?" – Nick Alexeev
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  • \$\begingroup\$ It's most likely a SOT-23 package voltage regulator, considering the location where it is and the designator U4. It has the marking V2MJ, but not sure what the output voltage is \$\endgroup\$ – Douwe66 Jun 5 '17 at 13:48
  • 1
    \$\begingroup\$ Give it up and purchase another one. It is only $5.99 USD at the Amazon link. You could pay more than that to just locate, purchase and ship a part to you to solder in. Next time be way more careful how you plug things in. \$\endgroup\$ – Michael Karas Jun 5 '17 at 15:04
  • \$\begingroup\$ This page says it is a AP7313-30SAG-7. Cheap lesson for $6. \$\endgroup\$ – StainlessSteelRat Jun 5 '17 at 15:30

That is probably a linear voltage regulator.

However, just replacing the obviously blown part will probably not fix the device. Quite possibly, other parts were exposed to high voltage too, just don't show any obvious signs of damage.

Toss this thing and move on. Be more careful next time.


Here's information about this tester with its circuit diagram. Per this thread U4 is 3 V regulator. Down the comment thread on that page you will find several links to the Aliexpress web site.

Remove fried component, and use multimeter in voltrop (diode sign) mode to identify the measurements on the board's pads of the regulator to see what happened to other devices soldered into the board. If reading will be less than 100, you have something else fried too.


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