The Power Hammer isn't actually difficult to repair.
Because it's durable.
In Durin's era, durability meant easy maintenance—to activate the Power Hammer, there usually was a trigger switch on the handle, with circuits inside, while the head of the hammer was a prime example of "crude workmanship".
The "crude workmanship" here is compared to the Light Sword.
After all, the working principle of the Power Hammer is pounding; making it too delicate could easily damage the internal activation system during recoil, so precision is not an option for this tool.
The hilt of a Light Sword, that is the epitome of refinement. According to Big Orange, he has no way to deal with a Light Sword hilt, but Power Hammers, there's not one he can't fix.