I have a Smartpool NC52 (Version 2) Wall Climber (aka Rupert, the pool butler). Smartpool Customer Service will email you the Repair Manual on request. The unit is very easy to work on with basic tools, a (cheap, Radio Shack) volt-ohm meter and tie-wraps. I would expect that this is true for other models also.
Recently Rupert stopped working. Following the simple diagnostic steps in the manual, I determined that the voltage at the power pack was correct (28-32 volts DC). The voltage at the cleaner end of the cable, where it goes into the pump motor, was only 1-2 volts instead of the normal 25-30 volts DC, however. What was surprising was that the voltage was low, rather than zero voltage from a broken wire. Since low voltage is a standard diagnostic test, this appears to be a known failure condition.
I replaced the cable and Rupert immediately started working. More interestingly, Rupert was moving faster and vacuuming more vigorously than he had for the last year or so. This implies to me that the voltage had been dropping gradually and finally got too low for Rupert to function. Because of this I would recommend periodically checking the voltage at the cleaner end of the cable and preemptively changing the cable if/when the voltage drops significantly. (I'm not sure what "significantly" is.)
Note - The strain relief where the cable enters the cleaner had torn about a year ago. On both the old and new cables I used two tie-wraps in a criss-cross to fasten the strain relief to the handle and strengthen the strain relief.
Note - Marina Pools (www.MarinaPoolSpaAndPatio.com) has the best online prices for Smartpool parts that I have found. They are also very helpful with questions over the phone.