I have an eight year old Minn Kota 55# thrust stern mount motor and noticed a big decrease in speed plus an increase in motor noise. I didn't want the expense of shipping and repair costs, so I decided to look at the schematic that came with the motor and opened up the top and bottom parts of the motor. I found out that both areas needed parts or cleaning and with the excellent support of Minn Kota's superb tech staff, was able to bring the motor to a like-new condition. (I had them on line for a total of 30 minutes/ six calls).
First, and easiest to test and replace was the speed control unit.
Hooking up a positive lead wire to any one of three leads on the controller and one lead to the negative side of a small lawn mower battery, I was able to find the speed that didn't work of the seven handle speed positions. Module ordered and replaced.
Second was to diagnose the noise coming from the lower unit. That required taking it apart starting with the two screws near the prop. I pulled out the core and this is what I found:
The contacts were dirty and the brass parts need light sanding to get corrosion off and since there was condensation in the housing, three new seals needed to be ordered. (Note: flat rate shipping is expensive, so order everything at once!)
Once everything was put back together and the motor tested (I had the armature in backwards and had to reverse it), the surprise, satisfaction and relief I experienced was that of having solved a problem that seemed insurmountable unless big bucks were paid to fix it.
parts list and schematic also found on Minn Kota's web site)
It's called Mike's Reel Repair ( http://www.mikesreelrepair.com/ ), and he's really helpful if you run into problems finding part numbers. I've been the neighborhood trolling motor fixer-upper, since my neighbors don't have the desire to learn how to fix them. they reimburse me for cost of the parts, and I do the repairs for them gratis. It's one of those deals where we do stuff for each other, benefiting our ability to fish and hunt together.
Was considering upgrading to a larger unit but don't have $600 laying around.
Did you do any maintenance on the cable system.....that seems to be where my issues are.