26oclock
Tearing down a dead NEMA-23 Clearpath SC.
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But how???

Cause of death - 6+ months of infrequent exposure to 'fresh' water.

This particular model did have the additional waterproofing shaft seal, but the electrical connectors weren't sealed with much care.

When it started throwing tracking error faults randomly, it was time to replace it.

Looking inside a wet Clearpath

I've used a handful of different sized Teknic Clearpath servos from the MC, SD and SC ranges, and an opportunity to take a peek inside the integrated drive mounted to the back of the servo was too hard to resist.

Clearpath SC servos mount the drive electronics inside a cast aluminium enclosure on the back of the motor

Undoing the screws lets us pull the integrated drive unit off the back of the motor and frame.

Mounted to the servo side of the assembly is a PCB which acts as a mounting interface for the optical encoder and interfaces to the motor's windings. The rest of the IO and drive electronics sit in the cast heatsink.

Exposed PCB stack mounted to heatsink, 3 wires connected to a PCB on the motor assembly

We can already see some corrosion products sitting near the 'bottom' of the heatsink.

Removing 6 more hex-screws separates the electronics stack.

Electronics removed from heatsink is a 2-PCB setup using a board-to-board connector

A better look at the extent of the corrosion products...

White corrosion/salts accumulated on bottom of both PCBs

The 'front' board has the optical encoder, IO and some power conditioning. The back of said board has mostly IO conditioning optocouplers etc.

Internal PCB on page of paper, hole cutout for encoder shaft, black Molex Microfit connectors for IO and power

Back face of encoder PCB with optocouplers, various SMD passives and some discrete regulation components

The control microcontroller, gate drivers/current shunts/FETs are on the rear-most PCB.

Internal PCB with large microcontroller, board-to-board connector, 3 gate-driver ICs and 6 surface mount mosfets

The rear-face of the control PCB has a cute thermal interface from the rest of the FETs, to a nicely machined step on the cast heatsink.

Rear of PCB with mosfets covered by white and orange thermal interface pad, electrolytic capacitors near edges, USB connector and LED

The USB config port is also mounted here, along with some bulk capacitors which have pockets in the heatsink.

Cast aluminium heatsink with a vertical flat face with machining marsks, corrosion residue around corners and walls

Closing thoughts

Running this servo so far out of spec in a wet environment worked far better than it had any right to, and packing the IO connectors of the replacement servo with dielectric grease seems to have prevented any repeated damage.

For the price, I've found the form factor and reliability of the Clearpath servos to make them a good choice for precision positioning, provided the mechanical system has sufficient external gearing and low total backlash.

The internal electronics design and integration reflects the solid design and build quality. Just wish the config and tuning software ran on something other than Windows...