HOW-TO GUIDE
How to Solder a Replacement Rotary Encoder Onto a Circuit Board
By the OhmSavvy Research Team ·
Safety: unplug the device and mind the hot tabs
- Disconnect mains power and remove batteries before opening the device. In mains-powered equipment such as amplifiers, large capacitors in the power supply can hold a charge after unplugging; keep your hands away from that section unless you know it is discharged.
- Mounting tabs need a hot tip and a longer dwell, and they stay hot afterwards. Clamp the board rather than holding it, and keep the iron in its stand between joints.
- Ventilate or use a fume extractor, and wash your hands after handling leaded solder.
Identify the encoder before you remove it
A common mechanical incremental encoder has three pins on one side and two on the other, plus two metal mounting tabs. The three-pin side carries the A and B channel contacts and a common (C) pin; on many parts the common is the middle pin, but check the datasheet. The two-pin side is a push switch, present only on encoders with a push-to-select shaft. Read any markings on the body, then note the details below before it comes off the board.
A, C, B pins
Two contacts and a common. They switch on and off in sequence as the shaft turns.
Switch pins
Two pins closed by pushing the shaft. Absent on encoders without a push switch.
Mounting tabs
Metal tabs through slots in the board. They take the strain of turning and pushing.
Detents
The clicks per turn. Some encoders have none and turn smoothly.
Pulses per rev
Full A/B cycles per turn. Not always equal to the detent count.
Shaft
Diameter, length, and flatted (D) or knurled, to match the knob.
Match every row of this table. Datasheets list the pulse and detent counts; if you cannot find one, count the clicks in one full turn of the old part. Then watch the A-to-common contact on a meter while you turn: if it closes and opens again within each click, there is one full pulse per detent; if it changes state once per click (closed at one click, open at the next), the part has half as many pulses as detents. Copy whatever the old encoder did, because the firmware was written around it.
| Attribute | Why it matters | If it is wrong |
|---|---|---|
| Pin layout and spacing | The part must drop into the existing holes | Pins will not fit, or the wrong pin lands on A or B |
| Pulses vs detents | Firmware expects a set number of pulses per click | Skips every other click, or counts two per click |
| Push switch | Some functions need a press to select | Menu or mute stops working |
| Shaft type and length | The knob must fit and sit at the right height | Knob loose, too proud or too deep |
| Bushing and thread | Panel-mounted encoders are held by a nut | Will not pass through or lock to the panel |
Encoder, not potentiometer
The process at a glance
01
Identify
Pinout, detents, pulses, shaft
02
Desolder
Pins, then the heavy tabs
03
Clean holes
Wick or pump, check the pads
04
Fit flush
Seated square, shaft aligned
05
Solder
Tack a tab, then pins, then tabs
06
Test
A and B toggle as you turn
1Desolder the old encoder
Start with the five small pins. Add a little fresh solder and flux to each, then clear it with a solder sucker or wick; fresh solder melts more easily than old, oxidised factory solder. The mounting tabs are harder. They are wider, sometimes bent over on the underside, and often connected to a ground area that pulls heat away. Straighten any bent tabs first, use a larger chisel tip, add fresh solder, and give them longer to heat. Work the tabs one at a time until the encoder lifts out without force.
If the old encoder is scrap anyway, you can cut its legs and tabs from the top side, lift the body away, and remove each leftover pin individually. That avoids levering on pads while several joints are half-melted. For the techniques themselves, see how to remove solder from a circuit board. If a pad does come away, our guide to repairing lifted PCB pads after desoldering covers the fix.
2Clean the holes and inspect the pads
Every hole must be clear before the new part goes in; one blocked hole stops the encoder seating. Hold the board up to a light and check you can see through each pin hole and both tab slots. Plated through holes on ground can resist a solder sucker; working from the opposite side, or wicking both sides, usually clears them, as explained in how to remove solder from a plated through hole. Then clean off flux residue with isopropyl alcohol and look at each pad for lifting or a cracked trace.
3Fit the new encoder flush and square
Push the encoder in from the component side until its body sits flat on the board. A tilted encoder wobbles when turned, puts strain on the solder joints, and can bind against a front-panel hole. If the shaft passes through a panel, check the alignment now: fit the board in the case loosely, or hold the panel in place, so you can see that the bushing centers in its hole.
The tabs usually snap into their slots and hold the part while you solder. Do not bend them over unless the original ones were bent; a bent tab can touch a nearby trace on the underside.
4Solder the tabs and pins
Tack one mounting tab first and recheck that the encoder is flat. Next solder the five signal and switch pins with a smaller tip: heat pad and pin together, feed solder into the joint, and stop at a small concave fillet. Finish by soldering both tabs fully, with enough solder to fill the slot, because they carry the mechanical load every time the knob is turned or pressed.
Keep heat and flux away from the moving parts. Many encoder datasheets give a hand-soldering limit of a few seconds per pin at a stated temperature, and many open-frame encoders are not designed to be washed, because flux or solvent can wick inside onto the contacts. Check the datasheet before cleaning, use flux sparingly near the body, and never spray cleaner into the shaft. A joint that looks dull or grainy needs reworking; see how to fix a cold solder joint.
5Test the A and B channels while turning
With the device unpowered, set the meter to resistance and probe between pin A and the common pin. Turn the shaft slowly. The reading should switch between a low value and OL as the contact makes and breaks. Repeat between B and common. Use resistance rather than the continuity beeper: contacts bounce as they switch, and a beeper can chatter even on a good encoder. Probe the top of each pin or its trace, so the test also proves the solder joints.
The two channels switch out of step, which is how the circuit tells direction. Turning one way, a typical contact sequence runs through four states per cycle; turning the other way runs it in reverse. Many encoders rest with both contacts open at a detent, but that varies by part:
| Step | A to C | B to C |
|---|---|---|
| 1 | Open (OL) | Open (OL) |
| 2 | Closed (low Ω) | Open (OL) |
| 3 | Closed (low Ω) | Closed (low Ω) |
| 4 | Open (OL) | Closed (low Ω) |
Finally, press the shaft and check the two switch pins go from OL to a low reading, and check each pin to the mounting tabs reads OL unless the schematic ties them together. For more on mapping contacts by hand, see how to test a rotary switch with a multimeter.
Common rotary encoder replacement mistakes
- Wrong pulse-to-detent ratio. The part fits and tests fine but skips or double-counts in use. Match the datasheet, not just the footprint.
- Levering the old part out. Pulling while one tab is still solid tears pads. Clear each joint fully, or cut the old part out.
- Encoder not flush. Wobble and panel binding follow, and the joints crack sooner.
- Starved tab joints. The pins end up carrying the turning force and fail first.
- Flux or cleaner inside the body. Sticky contacts give the same erratic behavior as the worn part you removed.
Connectors on the same board need similar care; see how to solder a ribbon cable connector onto a PCB.
Which iron suits encoder work?
This job swings between small signal pins and heavy tabs on ground copper, so a temperature-controlled iron with power in reserve and a choice of tips is the best fit: a fine chisel for the pins, and a larger chisel that stores enough heat to flow solder through a tab slot on a ground plane without a long dwell. Hot air can lift a whole encoder at once, though it heats the plastic body too, so it suits removing a part you are throwing away more than fitting the new one. Compare the options in our best soldering irons roundup.
Stations in our reviews
Five presets and digital 50–480°C control on a 100W station, for encoder tabs tied into large copper areas.
85W digital, ESD-safe station (70W iron) built for dedicated workbenches and professional use.
A 75W iron plus a 500W hot air gun in one station, for SMD and BGA rework alongside general soldering.
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Frequently asked questions
Can I replace a rotary encoder with a potentiometer?
No. They often look alike and both have three main pins, but a potentiometer is a variable resistor with end stops, while an encoder turns endlessly and switches two contacts on and off. The circuit reads them in completely different ways, so a potentiometer will not work in an encoder footprint, and the reverse is also true.
Why does my new encoder skip steps or count two per click?
The usual cause is a mismatch between detents and pulses per revolution. Firmware written for an encoder with one full pulse per click will misread one that gives half a pulse or two pulses per click. Check the original part's datasheet, or count clicks and pulses on the old encoder, and buy the same ratio.
Can I clean a worn rotary encoder instead of replacing it?
Sometimes. Contact cleaner sprayed into an open encoder can restore it for a while if the problem is dirt or oxidation. If the contacts are worn, the improvement rarely lasts. Many encoders are sealed or not designed to be cleaned, and replacement parts are usually inexpensive, so a new part is often the more reliable fix.
Do rotary encoders have a polarity or orientation?
They have no electrical polarity, but they do have a fixed pinout. The A, common and B pins must go into the matching holes, and the footprint usually only allows one orientation. If A and B end up swapped, the encoder still works but counts in the reverse direction, which is easy to spot when you test it.
What are the two extra pins on a five-pin rotary encoder?
On most panel encoders with a push-button shaft, the three pins on one side are A, common and B, while the two on the opposite side belong to a separate switch that closes when you press the knob. Check them on continuity: the pair should read open at rest and closed while the shaft is pushed in. If the device uses that press function, the replacement needs the switch too.
