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Old 01-09-2022, 12:27 PM   #6
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Default Re: Axis Q6034-E Speed Dome cam No Power (teach me about POE)

Originally Posted by Dannyx View Post
I think I already checked all major components and didn't find anything bad, hence why I started this whole thread, just in case someone spots something or knows from former experience a common cause of failure in PoE circuits.
Well, I don't know much about PoE circuits at all (probably less than you)... but from a power supply perspective, it looks like there are at least several buck/boost converters in there. If their MOSFETs and diodes are OK, just check resistance to ground on the output of each of these rails (so check resistance between ground and one end of each inductor - the "563F", "393j", and "183d" inductors, in particular.) If any are shorted or have a low resistance, that could be why your PoE injector is showing overload, as the buck circuit that converts the higher voltage over Ethernet struggles to "feed" whatever is downstream from it in the camera, due to one of these converters trying to feed possibly a bad IC or shorted ceramic cap.

Originally Posted by Dannyx View Post
I'll even try something more extreme: provide my own power after the buck converter to see if the camera does anything, just to rule it out. The 4 small output caps of those 2 converters are rated at 25v and although this is a pretty big PTZ camera which would make sense to run on something like 24v, I'm not sure they'd design it that close to the rating of those caps, so maybe the output is 12v or thereabouts - best to start off small. This will also allow me to monitor current in case something else downstream fails only when powered up and measures fine when "cold"...
Yes, that's another way to go about it... though I still recommend checking the resistances first so you don't end up wasting time trying to feed power into the circuit and then trying to figure out where it's going or what's shorting it (if anything.)
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