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Old 01-02-2015, 06:08 PM   #1
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Join Date: Apr 2013
City & State: Latrobe, PA
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Default Magicjack power adapter failure

I use magicjack plus. It gives me land line phone service for a small fraction of what Comcast charges. It has been a good service so far.
For those not familiar. The magicjack plus is powered thru a USB port (5 volts). Magicjack can be powered directly from your computer, but that means magicjack will not work when the computer is not on. It also comes with a power adapter module that converts AC to a USB 5 volts. With this adapter, the magicjack can be powered from the wall AC and can run independent of your computer. If you power it with the AC adapter, you will need to connect the magicjack to your router with a Ethernet cable.
I normally have it powered from AC with the adapter, but the adapter recently failed, so I had to power it with my computer USB. The same thing happened to my sister. Searching the net, I discovered that magicjack power adapter fail a lot.

I decided to trouble shoot the problem. I measured the 5V output of the power module to be only 3.5V. I took the power module apart to figure out why it failed. I found two 220uF 10V capacitors that were labelled "Low ESR" (C8 and C9). I measured the ESR of these caps and C8 measured 1.5 Ohms. I replaced that cap and it fixed the problem. Output voltage restored to 5V. These electrolytic capacitors do not fail suddenly, they gradually deteriorate. The output voltage of the Magicjack power module will drop gradually until it hits a critical level. The MJ will start to behave sporadically, then it will die completely.
If the cap fails with an ESR of only 1.5 ohms, then it must really need a super low ESR.

I do not recommend repairing these power modules. I did it out of curiosity. These modules are very cheap.
Magicjack is aware of the problem and offers a replacement. To contact them, go to and go to "support". They will ship you a new power module for about $5.35. Some people have reported that the replacement modules from Magicjack are no better than the originals and have had repeat failures.
Consider getting a power module from another source. There are lots of AC to USB power converter modules available on Ebay for only a few dollars. Search Ebay for "magicjack power adapter".
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