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BEWARE Cheap USB scopes! 
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LQFP144 - On Top Of The Game
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I had my DSO-220 scope hooked up to a 12v signal(testing a boost controller) for a while and all was well when all of the sudden Windows dropped the device(you know that sound when you unplug something). To make a long story short it fried itself($220) and my USB-to-Serial adapter. It's a miracle the ports on my laptop are still good.

After I took it apart there was the familiar but faint fried smell, but I couldn't find anything visible wrong with it. During inspection I found all sorts of diodes that were added after the board was designed/built.

I had it set to DC but was using + ground, that shouldn't have caused the melt down should it? Says 36v max.

-sean

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Tue Feb 17, 2009 2:51 am
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Flyback from a solenoid can go well above 36V which is what I would suspect here.

Jean


Tue Feb 17, 2009 3:09 am
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True, but I had a 2 amp diode to soak flyback, unless that wasn't enough.

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Tue Feb 17, 2009 3:37 am
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You would still think they would have protection so that power isn't back fed to the USB port.

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Tue Feb 17, 2009 3:41 am
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Gutted :-(

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Tue Feb 17, 2009 4:28 am
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LQFP144 - On Top Of The Game
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I'm kinda leaning towards this http://www.saelig.com/miva/merchant.mvc?Screen=PROD&Product_Code=PSSA002&Category_Code. I know I know didn't I learn the first time, but it looks significantly better than my last one :)

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Tue Feb 17, 2009 4:51 am
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I would think that 2A should be enough but maybe it's just not fast enough. But I agree with you that in any case power shouldn't be fed back to the USB port. That's simply stupidly bad design.

And thank you for the warning because I also have a cheap USB scope.

Jean


Tue Feb 17, 2009 5:19 am
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There's 99 ohms between the probe ground and the USB ground pin.

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Tue Feb 17, 2009 5:52 am
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