I have a pretty extensive Simnet setup on our L450, and just went through a learning
curve on troubleshooting, probably due to a near miss on a lighting
strike that brought the network to its knees.
The Simnet bus is pretty straight forward; terminator, devices, power, terminator. There is usually one terminator in the MHU due to the cable length. The other is at the end of the chain.
I found that having a couple of terminators available is handy for troubleshooting because it allows you to narrow down your network. I started out small and grew. For instance terminator+ MFD + power + terminator. If that works, add something else until it fails. By works I mean shows no errors as described below.
The terminator built into the mast head
unit is a challenge. So buying
an extra terminator is a good idea. For two reasons, debugging as noted above, and getting your system back up when you are out and about and your MHU fails. The second terminator enables you to disconnect the failed MHU and at least you get the rest of your system back.
Getting the layout of your simnet is very handy. If you call your product's technical support, they might send it to you. B&G received one from Lagoon
for my boat
model, and provided it or me, I attached it. (Note the terminators in the lower left and upper right (MHU) of the schematic). Otherwise, build one. They are not complicated - the biggest challenge is following the wires in your boat
. But, it starts at one terminator, and follows a single path of devices, a power point and to the terminator at the other end. Daisy chained devices are just part of the path, not tee'd off.
Checking voltage is a challenge since you need exposed wires. I found them in my Autopilot
Computer, where the simnet was connected to a terminal block.
The terminators are 120 ohms across the data lines. Two terminators on the bus are in parallel and result in a 60 ohm resistance on the data lines for a properly terminated bus. This is measured with the power off. If yours read 60 ohms, that is a good sign. You can find out which pins are voltage and which are data on the internet
. Connector pins are in order, power, power, ground, data, data. Looking at the end of a cable connector, with pin number 3 at 12 o'clock, the data pins are at 4 and 5 o'clock. 7 and 8 o'clock are power pins.
You can check your MHU by disconnecting the connector at deck
level (i.e. not have to climb the mast) and check the data resistance. If it is not 120 ohms (since it is just a single terminator), you found a problem. Seeing 120 does not say it works, just not seeing it say it does not work
Finally, you might be able to check your bus properties via you MFD. On my B&G (Navico supplied devices), I am able to select Network, and then Diagnostics. It shows me a count of receive and transmit packets, and the count of errors for receives and transmits. The B&G guys said the Rx and Tx errors should be zero. They have big packet errors and other errors, but they are not as important. Minimize your system, check to make sure Rx/Tx errors are zero, then add to it. No Rx/Tx errors is the rule
. In my case even a single MFD (a Triton 2) gave errors. I disconnected it, added another MFD and moved on.
The B&G technical support guys were GREAT! Use the option to let the system call you back, and keep your phone
with you. My wait times were 2 hours, and if you miss the call back, another 2 hours. Nonetheless they were very helpful.
BTW, this knowledge was gained over a week of non-stop troubleshooting my network since we were trying to get out of the hurricane
box. Hopefully yours will go faster.