I was working with one of Adafruit's CNC Rotary Encoders and made a mistake wiring. Well, long story short, I killed it. I am not sure exactly what I did, but I suspect I accidentally drove its outputs with an improper voltage.

To prevent the experience from being a total loss, I took the time to partially disassemble it.

The plastic cover around the screw terminals can easily be removed, exposing a PCB. 3 pins hold this PCB onto the rest of the assembly. After desoldering them, the component side of the board can be seen.

The board features a "7550" voltage regulator. The incoming supply is regulated down from whatever it is to 5V for the internal circuitry. C2 is the input smoothing capacitor, and C1 is the output smoothing capacitor.

D1 and D2 are light emitting diodes in series (likely IR) which are positioned under matching sensors in the upper part of the assembly. A "331" (330Ω) resistor limits the current through the LEDs.

The 3 soldered positions are a supply and 2 returns from the sensor package in the upper part of the assembly. Resistors R2 & R3 are pull ups, while caps C3 and C4 smooth out any spurious transitions of the signals. It seems most likely that the sensor assembly consists of two phototransistors, which can pull the pins of the "HC14", a schmitt-trigger inverter. This creates the signals A and B at a dependable logic level, and also the inverted A/ and B/ signals.

Diode D3 is a reverse current protection diode; in case VCC and GND are swapped, no current can flow. Interestingly it's on the GND side, while I thought it was more common to see on the VCC side.

If I cared to determine which component(s) I damaged, this is totally a board that could be reworked by hand. However, I don't plan to spend the time and instead will just pick up a fresh encoder from the store—and double check my wiring next time.

It might be fun to further disassemble the upper part, but the ring is glued on so I couldn't get into it in a hurry. However, you can see the 100 positions in the outer wheels. When the wheel moves, the different slots are either opened or obscured. When a slot is exposed, the phototransistor inside allows current to flow, creating the quadrature waveform.

I'm not sure, but the other slits & holes might be used for other encoder configurations.