Slip ring continuity test (2024)

One possible reason for the failure of the laser, tape sensor, or servo is a failure of the slip ring that connects fixed wires on the main board to wires on the rotating arm. These wires are tiny (30AWG) and while they're fairly well protected, it's not impossible to break them.

You can check for a failure of one or more slip ring connections using a continuity tester, typically a mode on a multimeter that will beep when you touch its probes to both ends of an unbroken connection.

Repair or replacement of the slip ring is very challenging, but knowing that the slip ring is at fault would at least save you the time/trouble of replacing a part that might well still be good.

Board connector

The slip ring connector on the main board (inside the bucket) is located near the top edge (if the scarecrow is rotated so that most of the writing is right-side up). The slip ring connector has 8 wires. Looking at the board with the key switch toward you, they are arranged from right (1, black) to left (8, purple).

The colored rectangles in the photo above mark metal pads that connect to the slip ring. These are easier to access with the meter's probe tip than the actual slip ring connector. Note that the solder pad connected to wire #3 (red) is the upper half of the broken oval (above #2, brown). All others are the lower half.

Rotating arm connectors

These are found at opposite sides of the squareish circuit board just above the rotating arm. The photos below show one of these boards with its cover, but no other parts are attached.

Testing tips

It is very difficult to check the slip ring continuity yourself because you can't see both ends at the same time. A helper is very helpful! 

If you cannot confirm continuity on one of the wires, make sure that you can confirm continuity on at least some of them, just to be sure of your technique. If you're checking a soldered pin on the rotating board, make sure you've scraped any conformal coating off of it. Also check that you continuity is indicated when you touch the probes to each other.

Possible repair

Once you're sure you have a break in the slip ring, there are two options. Both are challenging and are only summarized; you may wish to contact Rebecca Brown or David Brown (see Support/General) and find out whether we can do the repair for you. These instructions are incomplete and very abbreviated. If you wish to attempt this, again contact us to see if we can provide more details.

Slip ring replacement

The scarecrow must be pretty much fully disassembled to replace the slip ring. The slip ring is Senring model H0522-12-D (or -C, or -H). The stator wires are trimmed to 100mm placed inside some braided sleeving. The rotator wires are trimmed to 50mm. JST XH style crimp connectors are placed on wires 1-8 on both ends and these are inserted into 8-position housings.

Slip ring "repair"

While the slip ring internals can't be repaired, it is sometimes the case that a crimp connector broke off right at the end of the wire; this fix is relatively easy -- compared to replacing the entire slip ring -- with a small-gauge wire stripper, JST XH crimp terminals, and a JST XH crimp tool, and a very tiny flat-head screwdriver to flatten the locking tab of the original crimp and push it out of the housing. 

If one of the slip ring conductors is indeed faulty, there are 4 unused wires (white, gray, pink, light blue) at either end that may still be functional. You could crimp connectors to either end of one of those conductors and replace the original in its housing on both ends. The color doesn't matter so long as it's the same color in the same housing position on both ends.

Accessing the rotating connector

The arm side JST connector is on the rotating board under the plastic cover. You will need a 1.5mm hex key to back off the set screws that help secure the drive shaft inside the TPU adapter clamp in the PVC Tee and then remove that TPU adapter (possibly with pliers). Also remove the U-shaped clips that help hold the rotating board to the Tee (2.5mm hex key). You should then be able to lift up the Tee and carefully peel the cover off the board to access the connector.