Mitsubishi FX3UC-64MT/D Compact DC Power PLC

Status: EOL (End of Life). Compact connector-type PLC with DC power supply under FX3UC series, designed for small high-speed positioning and wiring-saving equipment.

✅ Model Code Explanation

FX3UC: Ultra-compact connector sub-series of FX3U

64: Total 64 I/O points on main unit

MT: Transistor output

D: DC24V power supply, Sink output

DSS: Same form factor, Source output variant

📌 Core Specifications

Power supply: DC24V (allowable range -15% ~ +20%)

Onboard I/O: 32 inputs / 32 outputs, DC24V input

Program memory: 64K steps EEPROM, supports RUN write

Power consumption: 11W; Built-in 5V bus supply: 480mA (for expansion modules)

Max I/O: Up to 256 local expansion points; maximum 384 points including CC-Link remote I/O

Dimensions: 59.7 × 90 × 74 mm, weight 0.35kg, IP10

Instruction speed: 65ns per LD basic instruction

🚀 Built-in Functions

1. 3-axis built-in positioning pulse output, directly drives servo/stepper motors (core advantage of transistor models)
2. High-speed counter: 100kHz × 6 single-phase channels, 50kHz × 2 two-phase channels
3. Expansion support: Analog, temperature, CC-Link, RS485 communication adapters; Note: No BD expansion boards can be fitted directly to main unit. Only external ADP adapters are supported.
4. Programming software: GX Works2; compatible with FX3U instruction set

⚠️ Selection & Replacement Options (EOL replacement)

1. Direct drop-in successor: FX5UC-64MT/D (same connector structure, program migration required, similar mechanical mounting)
2. Screw terminal alternative: FX5U-64MT/ES (terminal type, different wiring layout)

Migration notes: Most instructions of FX3UC are compatible with FX5UC, but high-speed positioning, soft elements and special registers differ. Positioning programs require re-commissioning.

📎 Comparison Notes

FX3UC-64MT/D: Sink output, 64K steps

FX3UC-64MT/DSS: Source output, 32K steps

Difference from FX3U-64MT: FX3U is AC-powered with screw terminals; FX3UC is DC-powered with plug connectors, smaller size for built-in machine installation

🔧 Typical Applications

Small multi-axis servo machines, packaging machines, screw fastening machines, inspection jigs, custom automation machines. Ideal for cabinets with limited space, high I/O count and multi-axis positioning requirements.

FX3UC-64MT/D Onboard I/O Assignment (Octal, fixed onboard, 32IN + 32OUT)

Rule: FX series X/Y use octal numbering; digits 8 and 9 do not exist. Onboard I/O addresses are fixed; expansion modules follow sequentially.

Important: X000~X005 high-speed inputs (5μs), used for positioning pulse and high-speed counter; X006~X017 default filter 50μs, filter time adjustable via D8020.

| Group 1 | X000, X001, X002, X003, X004, X005, X006, X007 |

| Group 2 | X010, X011, X012, X013, X014, X015, X016, X017 |

| Group 3 | X020, X021, X022, X023, X024, X025, X026, X027 |

| Group 4 | X030, X031, X032, X033, X034, X035, X036, X037 |

✅ Input summary: X000 ~ X037 (32 points total)

Output Y (32 points, transistor SINK type)

Fixed built-in positioning pulse channels: Y000(Pulse), Y001(Direction); Y002(Pulse), Y003(Direction); Y004(Pulse), Y005(Direction). These 6 points are prioritized for servo/stepper driving for 3-axis positioning.

✅ Output summary: Y000 ~ Y037 (32 points total)

Supplementary Remarks

1. Fixed onboard I/O: X000~X037 / Y000~Y037. I/O addresses continue sequentially for expansion modules (e.g. first 16IN/16OUT expansion: X040~X057, Y040~Y057)
2. Max local I/O total: 256 points (64 onboard +192 expansion); CC-Link remote I/O upper limit 384 points
3. Clarification: FX3UC uses plug connectors instead of screw terminals. The above are logical soft-element addresses, NOT pin definitions of the plug. Pinout wiring diagrams are separate.
4. Positioning allocation reminder: For 3-axis servo control, avoid using Y0/Y1, Y2/Y3, Y4/Y5 as ordinary outputs.

FX3UC-64MT/D Fault List & Hierarchical Troubleshooting Manual

Unit highlights: DC24V supply, plug connector type, sink transistor output, onboard Y0/Y1,Y2/Y3,Y4/Y5 for 3 pulse axes; no BD board, expansion via ADP/bus adapter; 5V bus max 480mA, easy overload; EOL.

Fault reading: Online diagnosis in GX Works2; fault codes stored in D8060~D8067, M8060~M8067 are corresponding fault flags.

1. Quick LED Indicator Check (No PC required on site)

Important note: When ERR is steady ON, all outputs are forced OFF and servo pulse output stops. Safety circuits should be implemented externally, do not rely solely on PLC internal stop protection.

2. System Fault Code List (D Register + M Flag)

3. Fault Troubleshooting by Category (Sorted by On-site Failure Frequency)

(1) Power Supply Faults (High-frequency for FX3UC DC version)

Symptoms: POW off/blinking, random ERR alarm, lost pulses, X input chatter, intermittent expansion modules

Troubleshooting Steps:

1. Measure PLC supply voltage: DC24V allowable DC20.4~DC28.8V; abnormal behavior likely below 20V
2. Polarity check: Reverse polarity burns the PLC directly on FX3UC-D
3. Disconnect all expansions and ADP adapters, power only main unit to isolate fault between onboard PSU and downstream short/overload
4. Calculate 5V bus load: Max 480mA onboard 5V. Analog, CC-Link ADP and temperature modules draw 5V current. Exceeding limit causes random freeze and ERR flicker
5. Fit fuse in 24V loop (1A recommended) to avoid permanent PLC damage from short circuit

Clarification: SS is input common terminal. Sink model SS connects to 0V. Do not mix with 24V supply, risk of short circuit.

(2) X Input Abnormality (No signal / Always ON / Random false trigger)

Symptom: Sensor activated but X does not light; or X triggers randomly without sensor signal

1. Sink FX3UC-64MT/D: X sinks current, SS to 0V, NPN sensors required; PNP sensors do not work directly
2. Sensor power supply: Avoid powering large quantity of sensors from PLC built-in 24V, voltage drop easily occurs
3. Filter setting: X0~X5 default 5μs high speed; X06~X37 default 50μs, modified by D8020. Increase filter for noise, reduce filter for high-speed counting
4. Connector inspection: FX3UC pin connectors suffer frequently from retracted pins, oxidation and poor crimping; higher failure rate than terminal FX3U
5. Measure voltage between X and SS with multimeter, distinguish sensor fault or damaged PLC input channel

(3) Pulse Output Fault (Y0/Y1,Y2/Y3,Y4/Y5, main pain point of this model)

Symptom: Servo does not move on instruction, lost pulses, positioning deviation, single-direction travel, overshoot, M8029 not completed

Note: Only Y0/Y2/Y4 support high-speed pulse output, Y1/Y3/Y5 are direction signals. Ordinary Y points cannot output high-speed pulses.

Troubleshooting checklist:

1. Program side: Enable flag for DRVA/DRVI/DSZR/PLSY, pulse channel conflict (one axis cannot be triggered by multiple positioning instructions simultaneously); D8140/D8142/D8144 are 3-axis pulse counter registers for pulse monitoring
2. Wiring: Sink output, check servo pulse/direction interface type match. Many servo drives are source-input type; series resistor or signal converter required. Pulse cable shielding, separate from power cables, terminating resistor for long cables
3. Load: Transistor output cannot drive high current directly; short circuit on Y will destroy transistor permanently
4. EMI interference: Servo power cable routed together with pulse wire, poor grounding → pulse loss, inconsistent positioning error each run
5. Special register check: D8130 (Max speed), D8131 (Base speed), D8132 (Accel/decel). Out-of-limit parameters cause no output or alarm
6. Isolation test: Disconnect servo cable, test Y pulse pin with oscilloscope/pulse meter, separate PLC pulse failure vs servo receive failure

(4) High-speed Counter Abnormality (X0~X5)

Symptom: Count value unchanged, jumping reading, incorrect count

1. Confirm high-speed input allocation; X0-X5 hardware high-speed port cannot be shared between counter and pulse input
2. Single-phase / two-phase mode, multiplication setting (M8198/M8199 etc.)
3. Encoder power supply, A/B phase sequence; reversed phase results in reversed count direction
4. Do not set excessive filter in D8020 otherwise high-frequency encoder pulses are lost
5. Sink encoder compatibility, shield cable single-end grounding for long runs

(5) Expansion Module / ADP Adapter Faults (FX3UC no BD board, ADP only)

Symptom: ERR flicker on power up, module not detected, analog signal jump, CC-Link disconnection

1. FX3UC expansion bus requires FX2NC-CNV-IF converter. Direct connection to FX3U modules fails recognition
2. Sum of 5V current calculation, over 480mA causes random module drop and crash
3. Hot-plugging expansion connector → high risk of burning bus chip (FX3UC connector fragile)
4. Analog module: Read module fault code via BFM29; check 4-20mA/0-10V wiring, 2-wire transmitter power
5. CC-Link ADP: Station number, baud rate, terminating resistor, single-end shield grounding

(6) Communication Fault (Programming port, RS485ADP, N:N, inverter MODBUS)

Symptom: PC cannot connect PLC, GOT disconnect, inverter read/write timeout

1. Programming cable: FX3UC Mini-DIN port; confirm driver, COM port, PLC model selected as FX3UC
2. RS485 ADP: A/B wiring no reversal, 110Ω terminating resistor at both bus ends; shield single-end ground
3. Communication flags: M8063, D8063; MODBUS detailed error via M8438/D8438 (timeout, checksum, format error)
4. Duplicate station ID, slave power off, excessive bus branches

(7) Program / Memory / Battery Fault

Symptom: Parameters cleared after power cycle, program missing, parameter error alarm on power up

1. BATT ON = lithium battery exhausted; part number FX3U-BAT. Replace battery while powered ON otherwise retentive M/D data erased
2. EEPROM program storage: Frequent RUN write to D-area accelerates EEPROM wear
3. Program password locked: Cannot upload program; online monitor available confirms communication OK
4. Standard Maintenance Workflow (Minimize secondary damage)
5. Power OFF, visual inspection: Burned connector pins, pin retreat, contamination, cable insulation damage, short marks
6. Remove all loads: Disconnect expansions, servo and sensors, power only PLC main unit
7. Power ON, observe LED, connect GX Works2 to read diagnostic code
8. Isolate fault category: Main unit hardware / external wiring / expansion module / program parameter
9. Avoid repeated power cycling with short-circuit fault; FX3UC DC supply has limited self-recovery and mainboard burnout risk
10. Common Misjudgments Encountered On-site
11. BATT LED ON ≠ PLC failure, only retentive data lost; machine can still run automatically
12. ERR blinking ≠ hardware damage; most cases are program operation error, communication timeout, expansion mismatch
13. 5V overload is the top hidden fault for FX3UC: symptoms are random freeze, positioning chaos, intermittent communication, hard to diagnose at first glance
14. FX3UC plug connector: poor crimping / loose pins occur far more often than FX3U terminal type
15. Burnt pulse Y channel: Y status shows ON in software monitor but no hardware pulse output; remedy: reassign channel or replace PLC
16. Fault Reset Methods
17. Program and operation error: STOP → RUN, auto cleared for most cases
18. Latched M8068 operation error: Software force OFF required; power cycle will not clear
19. Fatal hardware fault (M8061): Remove hardware fault then power cycle
20. Communication fault: Auto reset after communication recovery; M8127 available for manual reset
21. Spare & Replacement Guidance After Failure

FX3UC-64MT/D EOL; preferred connector replacement FX5UC-64MT/D

Pulse registers and positioning instructions partially compatible, special register mapping differs

5V bus capacity and expansion adapters differ, positioning and high-speed counter program re-commission mandatory

Mitsubishi FX Series DC24V Powered CPU List (Suffix D = DC supply; DS = screw terminal sink; D = connector sink; DSS = source; TS = spring clamp terminal)

Quick naming rule:

D: DC24V supply, connector type (FX3UC / FX5UC)

DS: DC24V supply, screw terminal, sink output

DSS: DC24V supply, source transistor output

MR: Relay output; MT: Transistor output

Your model: FX3UC-64MT/D (EOL)

1. FX3UC (Connector, DC supply, EOL, compact)

FX3UC-16MT/D

FX3UC-16MT/DSS

FX3UC-32MT/D

FX3UC-32MT/DSS

FX3UC-64MT/D ✅ Your model

FX3UC-64MT/DSS

Features: No BD board, expansion via ADP; onboard 5V bus max 480mA; built-in 3 pulse axes

2. FX3U DC Screw Terminal Models (DS, phasing out)

FX3U-16MR/DS

FX3U-16MT/DS

FX3U-16MT/DSS

FX3U-32MR/DS

FX3U-32MT/DS

FX3U-32MT/DSS

FX3U-48MR/DS

FX3U-48MT/DS

FX3U-48MT/DSS

FX3U-64MR/DS

FX3U-64MT/DS

FX3U-64MT/DSS

FX3U-80MR/DS

FX3U-80MT/DS

FX3U-80MT/DSS

3. FX3G DC Models (DS, EOL ongoing)

FX3G-14MR/DS

FX3G-14MT/DS

FX3G-14MT/DSS

FX3G-24MR/DS

FX3G-24MT/DS

FX3G-24MT/DSS

FX3G-40MR/DS

FX3G-40MT/DS

FX3G-40MT/DSS

FX3G-60MR/DS

FX3G-60MT/DS

FX3G-60MT/DSS

4. FX5UC (Connector DC supply, direct successor of FX3UC, active iQ-F)

FX5UC-32MT/D

FX5UC-32MT/DSS

FX5UC-32MT/DS-TS (spring terminal sink)

FX5UC-32MT/DSS-TS (spring terminal source)

FX5UC-32MR/DS-TS (relay spring terminal)

FX5UC-64MT/D

FX5UC-64MT/DSS

FX5UC-96MT/D

FX5UC-96MT/DSS

Features: Built-in 4 pulse axes, standard Ethernet, higher 5V bus capacity than FX3UC

5. FX5U DC Screw Terminal Models (DS, active iQ-F)

FX5U-32MR/DS

FX5U-32MT/DS

FX5U-32MT/DSS

FX5U-64MR/DS

FX5U-64MT/DS

FX5U-64MT/DSS

FX5U-80MR/DS

FX5U-80MT/DS

FX5U-80MT/DSS

6. FX5UJ Economy DC Models (DS, economy iQ-F)

FX5UJ-24MR/DS

FX5UJ-24MT/DS

FX5UJ-24MT/DSS

FX5UJ-40MR/DS

FX5UJ-40MT/DS

FX5UJ-40MT/DSS

Supplementary Notes

1. All units listed have DC24V main unit power supply, not DC24V input type (AC powered CPUs also have DC24V X inputs, a common confusion point)
2. Q/L/R large PLC series have almost no CPU with onboard DC24V supply; they use rack + separate DC power modules and are excluded from this list
3. Selection replacement table for your unit

FX3UC-64MT/D → FX5UC-64MT/D (connector sink, same mounting, priority replacement)

If rework wiring to terminals: FX5U-64MT/DS

4. Suffix explanation:

D: Connector, sink output

DSS: Connector, source output

DS: Screw terminal, sink

DSS+TS: Spring clamp terminal, source