Mitsubishi Electric MELSERVO-J4 (MR-J4) alarm AL.16: Encoder initial communication error 1
Alarm AL.16 on a Mitsubishi MR-J4 servo amplifier is Encoder initial communication error 1: an error occurred in the communication between the encoder and the servo amplifier during initial communication. The detail number (16.1 to 16.F) tells you which part of the exchange failed.
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When it happens
- At power-up, when the amplifier first establishes communication with the encoder
- After a motor, encoder cable or amplifier replacement
- On multi-axis MR-J4W units, at power-up when an unused axis is not disabled
Reading the subset
| Subset | What it tells you |
|---|---|
| 16.1 / 16.2 | Receive data error 1 / 2: cable, encoder compatibility, amplifier or encoder. |
| 16.3 | Receive data error 3: disabled-axis switch, cable disconnected, communication method parameter, parallel-drive setting, control power, amplifier or encoder. |
| 16.4 | Encoder malfunction. |
| 16.5–16.7 | Transmission data error 1–3: same checks as 16.1. |
| 16.8 | Incompatible encoder: motor or software version not supported by the amplifier. |
| 16.A–16.F | Process error 1–6: amplifier or encoder. |
Likely causes and checks
1Encoder cable disconnected, open or shorted
- Points to it
- Alarm at every power-up; cable recently moved or replaced.
- Check
- With power off, check the encoder cable for disconnection and shorts; replace or repair it.
2Wrong encoder cable communication method setting (two-wire / four-wire)
- Points to it
- Detail 16.3 after commissioning or a long cable change.
- Check
- Check [Pr. PC22] on MR-J4-_A_, or [Pr. PC04] on -B, -WB, -RJ010 and -GF amplifiers.
3Unused axis not disabled (MR-J4W multi-axis)
- Points to it
- Detail 16.3 on an axis with no motor connected.
- Check
- Set the unused axis as disabled with the disabling control axis switches (SW2-2/SW2-3/SW2-4).
4Unstable control circuit power supply
- Points to it
- Detail 16.3 together with brief control-power dips.
- Check
- Check the control circuit power supply voltage for instantaneous power failures.
5Incompatible motor or amplifier software version
- Points to it
- Detail 16.8 after fitting a newer motor or linear encoder.
- Check
- Check that the motor or encoder model is supported by the amplifier and its software version.
6Amplifier or encoder failure, or noise near the device
- Points to it
- Cable and settings check good.
- Check
- Replace the amplifier and check repeatability; if it repeats, replace the motor; if it still repeats, check noise, ambient temperature and vibration.
Telling it apart
- AL.16 is an initial communication error, raised while the amplifier is first establishing contact with the encoder. AL.20 (Encoder normal communication error 1) is raised during normal communication after that, so it more often points to noise, shield termination or a cable failing under movement.
- Third-party lists sometimes define AL.16 differently; the Mitsubishi troubleshooting manual is the reference.
- Detail 16.3 has extra causes (disabled-axis switch, communication method, control power) that 16.1 does not.
Relevant parameters
| Parameter | Name | Why it matters |
|---|---|---|
| PC22 ([A]) / PC04 ([B] [WB] [RJ010] [GF]) | Encoder cable communication method selection | Must match the cable type (two-wire or four-wire). |
| PF40 | Parallel drive setting | Listed as a cause of 16.3 in parallel drive systems ([B]). |
Evidence to collect
- Full alarm and detail number (for example 16.3)
- Amplifier model and software version
- Motor model and encoder cable part number/length
- Settings of [Pr. PC04] or [Pr. PC22]
- Result of swapping the amplifier or motor
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