For what its worth, we've had similar experiences as Rain Again, but have failed 7 computers (power transistor and fuse issues). According to Navman, these were the only ones to have ever failed.
Currently experiencing display head problems (3380) where the unit will shut down recording a loss of power error after its manually turned back on. Other instruments are fine (i.e. no loss of power). We've completely rewired the high and low power supplies to the units with no change to the situation (carried out by a Navman dealer who is out of ideas apart from replacing it with another brand).
Navman's/ Navico's solution is to play spare parts surgery with us picking up the parts at RRP. We're about to have our last roll of the dice to resolve it but as we haven't resolved systemic AP problems over 3 years since installation, expectations are low. The fall back solution is replace instruments with those from outside the Navico stable.
While others people's mileage may vary, its difficult for us to see the product or product support in a favourable light. Over the time and approx 18,000 Nm, it's cost many times the cost of the unit in terms of replacements parts, air freight, additional crew and missed schedules.