Anyone that has Garmin TM 150 hooked up, friendly FYI
the "pause sonar" item on your menu doesn't stop the transducer from pinging. It merely stops the screen from advancing.
the " Stop Transmission" menu stops the tm150 from pinging.
I may have ruined mine due to this little detail.

i took the boat out today for a test and the 840 was barely reading the bottom In 20 ft of water. Reset everything to factory , no difference.
Max gain, no difference,
its either the 840 or the 150, but something is wrong.