ebass,
thank you for your inquiry.
you said that you recently returned the MFD12 for service & software updating. Was the software of the MFD8 also updated so as to ensure that both are running the same version?
It is important that ALL MFD's on the network are running the same software version.
The current version of the NN3D software is v2.13. Instructions for updating and the software itself can be found under the support page of the MFD8 and the "software" tab.
secondly, which of the two units on the network is configured to be the "Master" ? Have you ensured to go into the installation wizard on that unit and set the DHCP server to "ON"
if the MFD12 was originally the master this may have been erased during the software update procedure and you will have to simply go back and set tis to "ON".
Finally, if both level of software are the same and one of the units is set properly as the Master, what is the actual source of the depth information (i.e- are you running one of our DFF echo sounders or is there a "smart transducer" somewhere that provides this digital depth information?). to find this go into the installation of the master unit, under the "Global" tab, under the "Data sources" tab, under the "depth" source what is it set for?
this should be the same on both the MFD8 and the MFD12.
If all the above are correct there may be a transducer issue, like turbulence caused by marine growth or some other issue. when was the last time the transducer was inspected? If the boat is still in the water you may need a diver to inspect the face of the transducer.
Please report back, and we'll see what we can do to help you resolve this issue.