Simrad SimNet Noise Filter?

Actually it's the opposite.  Right now there is no "filter", just that thing I posted (the small "plug" with the red end, which i suspect is just a termination resistor).

From the pictures it definitely looks like a 220uF capacitor (the shape is consistent, it's not a small pico cap).

I'll know more when it shows up - as I think you mentioned, it's not a very common part and was difficult to find.

So with or without the additional terminator that is currently installed, the 508 acts the same.  Its solid while the SimNet is powered up, but will not come back to life after a power cycle.  Makes no discernible difference if that plug is installed in the 3-prong connector under the mast step.

The very curious thing is that without that terminator installed, powering down the network takes a very long time.  I have an extra Triton2 at the Nav station (that is powered only by the SimNet bus) and when you turn off power to the network, it remains on for a long time (minutes).  If the terminator is installed, the network powers down "faster" in less than a minute.  But either way it seems strange?  This is the red-tipped terminator, so I don't believe it has any capacitance, and technically shouldn't touch the power side of the bus cables.  But that is the observed behavior.

So when i'm back on the boat this weekend, I need to get out the multimeter and see what's going on...

Totally agree.  There is something fishy going on.

I'm curious to your statement about the bus vs voltage?  I guess since it's working the implication is that there is sufficient voltage getting to the mast top?

Why should it "come to life" when you un-plug/plug it in, vs just turn the power on...?

Yes, the B&G's have a diagnostic page.  It shows single digit "fastpacket errors", everything else is 0 and the bus load is around 17%.

I guess I can measure the voltage at the bottom and assume a certain voltage drop.  So it would only really be an issue if the voltage at the bottom was pretty low (like 11v).

My noise filter is arriving today, I'll swap that in first and see what happens.

I'm still also going to verify one, robust N2k power tap.

I have a N2K ShipModule to USB adapter (not installed), so theoretically I could examine it further on a laptop (I assume there are some pc based diagnostic tools?).  I also have an oscilloscope so I could really get all technical on it and see the shape of the signal.  That panbo article goes into it a bit:

... screen #1 shows a very short, simple network with no terminating resistors — which at least partially accounts for the ringing that follows the nice square NRZ waves, as demonstrated in screen #2, in which the same backbone has some terminator-style resistance added. Screen #3 shows what’s actually happening with 13 active sensors and about 60 meters of SimNet cabling. Apparently it works, but those waves are looking a little raggedy. Or were until he installed a SimNet Noise Filter as seen in screen #4...

So I definitely don’t have the filter.  The one I ordered just arrived and looks like this:

The filter just arrived and it doesn’t look anything like the termination plug that’s in there now.