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EMate 300 main board repair DZ1

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Hello all.  

I just picked up an eMate 300 which will run off its battery fine, but is in need of repair because it was ran off of a non original power supply.  On the main board there is a component marked DZ1 right next to the power input that got very hot and is fried.  I am assuming it is a zener diode to regulate the input voltage, it has markings on it "721 KV"  Can anyone tell me the value of this component for sure?  Does anyone have a schematic of the board?  I have a good suspicion that this is the only damage and if I know what value this zener is I could fix it.

Thanks in advance.

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I think it's an M7 diode, since the marking on the chip is more like "M721KV" on my one.


Here’s a data sheet:



So I desoldered it and did some basic testing - sadly I don't have a 1kV voltage reference to test with, but I tested up to 25V reverse bias and it didn't pass any current (it has a 0.651V drop in the forward bias direction, didn't write down the current but the datasheet says it should pass an amp).


Since it's for PSU protection, there's a good chance it is indeed that 1kV device, and even if you can't find something like that locally, an equivalent in the same package would likely be fine.


If you’re not worried about plugging in a backwards PSU you could just leave it out - as long as you don’t repeat the same mistake(!)


However, there is a fuse you should probably test on the other side of the board (I should have taken a photo) as that may also be blown. 



Edited by aladds
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