Re: what makes a autopilot 55 control board fry?
I have the same control board on my 1995 Minn Kota 42# 812 AP, actually the control board I have is 230-4005D but the replacement board is the same as yours.
Mine worked fine on the bench and on the water but corrosion at the foot pedal connector caused me to clean all the connections and lubricate with silicone grease to waterproof. The on/off switch was intermittent at the foot pedal and wiggling the harness would solve the problem for a short time
While cleaning the connector attached to the motor for the foot pedal control with a wire brush I inadvertantly left the power cable attached, normally this wouldn't have been a problem as I usually leave the battery switch off (BEP marine charge controller) but I was charging the battery's and forgot the switch was on.
Needless to say suddenly my motor would not rotate afterwards but the autopilot and steering work fine. Testing with a voltmeter indicated I fried the speed controller after much time was spent making sure the foot control was not the problem (ohm-meter testing).
I went on a search for a used part but all I found were junk control boards, I found three identical used trolling motors of various years all with the same problem....speed controller shot. I wasted a lot of time testing other peoples used trolling motors (that were advertised as working!) until hooked to a battery showed they were junk also.
It is my opinion that these control boards are common failure components for these motors, I cannot comment if the newer 230-4043 boards are better but from the pictures I have seen they look like cheap chinesse knockoffs as Minn Kota list these boards as "no longer available" and the connector harness does not have the rubber seal integrated. I am assuming you are looking at the Northland marine website as they stock them online at $75. Apparently Sears Parts Direct also lists the control board but I cannot comment on availability.
I have investigated a separate motor speed controller such as used in electric scooters as they seem to be more durable and around the same price, wiring in a separate box with a speed control dial on the foot pedal is something I would do for reliability.
I think the foot pedal connector is 90% of the problem with failures of these boards since any corrosion at the connector will cause a short and destroy the speed control function, I have cut the connector out of the circuit and wired my foot pedal direct now since I am sure this is why they fail all the time.
With the cost of a decent replacement at $1200CDN or more for a Autopilot equipped motor, I will fix what I have...I can see why people buy a kicker motor for trolling instead of fooling around with electric motors. The weight increase if you count batteries is the same. If it wasn't for the very handy feature of foot control, autopilot and quiet running I would do the same and forget this electric non-sense.
I may buy the same controller as you require...but only once. If it dies again I will upgrade the speed controller with an aftermarket version and custom wire it in. For something as simple as a PWM speed controller Minn Kota makes a crappy one...for example how hard would it have been to wire in a mercury switch to detect when the motor is tilted so it wouldn't actuate? Pfft!
I have talked to a couple of Minn Kota authorized repair places in my area and both were surprised that mine worked for so long, they all recommended complete replacement instead of repair...of course.
I have heard motorguide is no better and harder to get parts for, there is no cheap reliable alternative it seems.
Good luck with your repair, it is easy to swap out the board with a screwdriver and needle nose pliers to pull the board connectors. Make sure you take a picture of the connections so you don't fry your new board. I will be taking the same route as you are and throw another c-note at this thing. I would recommend sealing the wire connector with silicone grease to prevent corrosion as a minimum, any short there has dire consequences obviously.
