Originally Posted by southace
My raymarine does the same! I have to switch to standby and re-engage it it's painful fault!
It may be an unrelated problem, but the Raymarine chartplotters are very sensitive to low voltages. It's worth checking the voltage at the chartplotter when it's on.
A good clue is if the problem happens when the battery voltage is low, or other equipment
is turned on (such as the autopilot as in the OP case) then its very likely low voltage is the cause. If its a random problem it's more likely it's a different fault, such as a software
Another diagnostic test is to turn the screen brightness down very low. This reduces the power draw and voltage drop in the wiring/ connections. If the problem stops it suggests a voltage related problem.
These tests are not foolproof, but are useful indicators