This goes with 12VDC circuits or 440VAC circuits: ---statement removed---.
Here’s how I’d do it (as long as the steaks on the grill still have a little cooking time to go): (note that I’ve only peeked at the PCB, I didn’t reverse engineer it nor do I have schematics)
Disconnect the RJ45 (connection to SSC) from the suspected port (Smart String Output) so the load is not connected to the suspect fuse. Ensure power is provided to the Smart String Hub.
Looking at the component side of the board with the “( c) Robert Jordan†at the top of the PCB, place the negative voltmeter probe on one of the COM rails such as the black wire on the 20/24pin connector and the red or positive probe on the RIGHT SIDE of the fuse. If you read 12V then your fuse is good, if not, it’s replace fuse time.
An alternate method, with the Hub POWERED OFF and the load (RJ45) disconnected from the suspect port would be to use the ohmmeter function (low ohms or diode check/beep setting) of your DVM and place one probe on the RIGHT SIDE of the fuse and the other probe on one of the YELLOW wires of the 20/24pin connector. If you show zero ohms your fuse is good. Note: the LEFT SIDE of the fuse connects directly to the positive 12V rail, it should always read zero ohms.
Of course, you could ohmmeter directly across the fuse, but too many times I’ve seen a “good fuse†and the PCB electromechanical connection of the fuse failed – the fuse warms to the point that the link doesn’t fail but the soldering of the fuse mount to the PCB foil has gone cold or crusty or some other failure. Ohming from a known supply point to a known load point is my usual method.
I hope this helps.
joe
RJ - I haven't blown one yet, though I haven't put any power to anything yet either! So that may not be as grand a claim as it sounds!
OK, so a short at normal power levels would blow the fuse but not make any visual mark. Good to know. I suspect the easiest way to check a bad fuse would be to look for voltage across it with everything running?. Good fuse should show 0V, bad would show 12V. Or look for resistance with everything off/powered down.
Filing this tidbit away for future reference!