So what is happening relates to what we call the "Data Master". The first NavNet on your network takes charge of talking on the 2000 bus for the entire NavNet network. The rest of your MFDs are listening to the 2000 but do not talk. If you conduct a route, the data master passes the steering instructions to the bus and your pilot. The issue stems from the Simrad has a source setting that picks which source is allowed to drive the pilot. It is looking for the one particular unit that was setup as its source. It gets the data and all works. So how does one become the data master? it is the first Navnet powered ON. Think of it as a talking stick that if that first unit gets powered OFF later, it will hand the talking role to another MFD on the network. What is happening in your case is that one day you are powering ON the one MFD first and as the data master that the Simrad is looking for it works, because it is getting the data from the source that was selected/set for. The other case is when you power up the other MFD first and it becomes the talker. The MFD that the simrad is looking at is only listening and provides it no data. While the other MFD is talking; the simrad won't listen because it isn't the selected source established in its settings.
Your solution is simple. Just ensure you turn on the same Furuno MFD "first" every time that you power up. It needs to be the MFD that the Simrad is looking for data from. It will take the talking role for the NavNet network and Simrad will listen to it. If you focus on your MFD power up order, it will work every single time for you regardless if you have one or more MFDs ON. Just ensure if you are going to run only one MFD to use the one that the simrad was setup to look at. Hopefully that makes sense.
