I need help identifying what I think is a resistor

[killerkevdog]

I bought this (EN-SW10g-001) Eagle Eye 8 port Gigabit POE+ switch, new online.  It never showed any lights or any signs of life.  I got a replacement switch and decided to see if I could find out what the problem was on this one.  I looked at the new switch and it has a completely different power supply board.  There are two boards underneath the cover.  The power supply board has a component that is blown. See Pics, It is labeled (R42).  Im guessing its a resistor.  Is there any way to figure out what it is? Using a multi-meter?  Does anyone know where I could find the right component?  Could I use an external DC power supply and splice it in?  Any thoughts would help.

Thank you

[Whales]

That resistor looks like it's for passing a high current.  It might be a current shunt resistor or a fusable resistor.  I do not know of a way of finding the resistor's value other than trying to find other boards of the same model.  It could be anything from 1milliiohm to 100milliohm.

It's almost a guarantee that the resistor is a victim, not a cause.  Something is shorted in the circuit.  Often this is a mosfet, rectifier or transformer.  If you don't fix this then the resistor (or another part) will immediately blow again.

Is this a bit of copper shorting this connector?


I love how crooked those big packages are.  They be groovin.

[NPG]

I agree, that piece of copper or whatever it is looks out of place.

If whatever is on the other side of the board in that place is a cap, resistor, or diode, then the piece of material shouldn't be on the bottom.

[temperance]

The power supply controller is a TEA8918 which is a PFC+LLC controller. The burnt resistor is the PFC section current sense resistor.

[golden_labels]

Thanks for good quality photos, killerkevdog.

That salmon-colored thing is not copper. It’s translucent, as you can see by the shadow it casts.

Perhaps it is some adhesive, that got there by accident? No idea, if it should be there. But I doubt it would pass any current significant enough to blow up a resistor.

If user temperance (above) is right, then I’d not continue to simply replacing it. Rather remove it, and check if there is no shorts to ground. If not, also check the outputs and whatever this power supply was powering. No point in putting a new resistor, if it’s going to be blown up too.

[temperance]

If user temperance (above) is right, then I’d not continue to simply replacing it. Rather remove it, and check if there is no shorts to ground. If not, also check the outputs and whatever this power supply was powering. No point in putting a new resistor, if it’s going to be blown up too.

That resistor will blow up again if you only replace the resistor. The half bridge LLC is probably broken and shorted the PFC output.