Let me clarify a few things that might help diagnose the problem. Previously, I tested the voltage at the chart plotter. I have a solar panel that feeds the batteries when off the boat. At the beginning of all these tests, the batteries are fully charged from the panel. So with the batteries charged (12.7 v), measuring at the chart plotter power cable, I got 12.2 volts with battery 1 only, 12.3 volts battery 2 only and 12.3 with both on. When I started the engine, I got 13.1 volts. Note that the was chart plotter unplugged so I did not confirm that it would have started acting up when plugged in (the behavior is inconsistent). I am guessing that the voltage drop is expected and 12 volts is well within the spec of the B&G. I am presuming this eliminates the under-voltage possibility. I previously have tested the voltage at the batteries from the alternator but did not write it down because it seemed OK (about 14 volts). I also did the AC voltage test by measuring AC at the battery terminals with the engine running and that was less than the 50mv that was supposed to indicate bad diodes.
Is it still possible it is a voltage regulator problem and how would I test? To Gary’s message: I still think you have a noise/grounding problem. If noise gets into one of the inputs, say the NMEA, there is usually a buffer to handle excessive inputs. If that buffer gets overloaded, the chart plotter might act goofy until the buffer gets emptied. I would make sure you have a single point grounding system that all goes back to one ground point. Make sure all connections are tight. The NMEA was unplugged when it went crazy, so it is not getting in that way. I guess it is still possible to have noise from the DC input? Thanks- Dave Aries 1990 C&C 34+ New London, CT
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