Mitsubishi A1S61PN Power Module: Complete Guide to On site Troubleshooting and System Maintenance

Mitsubishi A1S61PN Power Module: Complete Guide to On site Troubleshooting and System Maintenance

In the field of industrial automation, Mitsubishi MELSEC AnS series PLCs are widely used in small and medium-sized control systems due to their compact structure, reliable performance, and rich I/O expansion capabilities. As the heart of the system, the stability of the power module directly determines the operational reliability of the entire PLC system. A1S61PN and A1S62PN are two mainstream power modules in this series, with a wide input voltage range (100-240 V AC), output 5 V DC 5 A or 3 A, and a 24 V DC 0.6 A (A1S62PN) output capability.

However, in long-term operation, engineers often encounter faults such as POWER LED not lighting up, system unresponsive, inability to drive output loads, and triggering overcurrent or overvoltage protection. This article is based on Mitsubishi's official technical manual, combined with actual on-site experience, to systematically sort out the selection points, installation specifications, common fault phenomena and troubleshooting steps of A1S61PN and its related power modules, and provide replacement suggestions for discontinued modules to help engineers quickly restore system operation.

Overview of A1S61PN Power Module Technology

1.1 Main specifications

A1S61PN belongs to the MELSEC AnS series power module, and its core parameters are as follows (compiled from the manual):

Project A1S61PN A1S62PN

Rated input voltage 100-240 V AC (+10%/-15%) 100-240 V AC

Input frequency 50/60 Hz ± 5% 50/60 Hz ± 5%

Maximum input apparent power 105 VA 105 VA

Rated output current (5 V DC) 5 A 3 A

Rated output current (24 V DC) -0.6 A

Overcurrent protection (5 V) 5.5 A or above action 3.3 A or above action

Overvoltage protection (5 V) 5.5-6.5 V 5.5-6.5 V

Allow instantaneous power outage time of 20 ms or more

Voltage endurance primary secondary: 1500 V AC Primary secondary: 1500 V AC

Weight 0.60 kg 0.60 kg

Dimensions 130 × 54.5 × 93.6 mm 130 × 54.5 × 93.6 mm

1.2 Applicable occasions

A1S61PN: Provides pure 5V DC 5A output, suitable for systems that only require logic power, such as CPU modules, I/O modules, and special function modules.

A1S62PN: Provides an additional 24 V DC 0.6 A output, which can be used to drive low-power sensors, relays, or provide auxiliary power to output modules.

1.3 Important protection functions

Overcurrent protection: When the current of the 5V DC circuit exceeds about 110% of the rated value, the protection circuit will activate, cut off the output, and the POWER LED will turn off or dim. Power on again after eliminating the cause of overload.

Overvoltage protection: When the 5 V DC voltage rises to 5.5-6.5 V, the protection will activate and the output will be turned off. At this time, power off and restart is required; If the fault persists, the module may be damaged and needs to be replaced.

Instant power outage tolerance: can withstand up to 20 ms of power interruption. If the power outage lasts for more than 20 ms, the CPU will reset and the system will be reinitialized.

Installation and selection precautions

2.1 Installation location and environment

The power module must be installed in the designated slot (usually the leftmost or rightmost) on the main substrate (such as A1S32B, A1S38B) or expansion substrate (A1S65B, A1S68B).

The installation environment must meet the following requirements:

Environmental temperature: 0-55 ℃

Relative humidity: 10-90% (no condensation)

Non corrosive gas, conductive dust, strong magnetic field

Installed inside the control cabinet, with a minimum protection level of IP54

2.2 Selection calculation: 5 V DC total current consumption

The key to selection is to calculate the total 5 V DC consumption current of all modules, ensuring that it does not exceed the rated output current of the power module.

Steps:

Refer to the manuals of each module to obtain the 5 V DC consumption current. For example:

A1SHCPU：0.3 A

A1SX41 input module (32 points): 0.08 A

A1SY41 output module (32 points): 0.50 A

Special modules such as A1SJ61BT11:0.40 A

Add up the 5V current of all modules.

If an expansion board without power supply (A1S52B, A1S55B, A1S58B) is used, the module current on it is also provided by the main board power module and needs to be included.

The total current must be less than the rated output current of the power module (5 A for A1S61PN and 3 A for A1S62PN), with a 10% margin reserved.

2.3 Consideration of voltage drop for extended substrate

When using passive expansion substrates such as A1S52B (S1), A1S55B (S1), A1S58B (S1), etc., the 5V power supply is transmitted from the main substrate through the expansion cable. Due to the resistance of the cable, there will be a voltage drop. Manual requirement: The module in the farthest slot must receive a voltage of no less than 4.75 V.

Computational Methods

The bus resistance of each slot on the main substrate is 0.007 Ω, and the expansion substrate is 0.006 Ω.

The cable resistance depends on the length (e.g. A1SC07B is 0.036 Ω).

Total voltage drop=main substrate voltage drop+extended substrate voltage drop+cable voltage drop.

Usually, the output voltage of the power module is above 5.1 V, and it is necessary to ensure that the total voltage drop is ≥ 4.75 V.

On site experience: If the load on the expansion substrate is heavy or the cable is too long, it is recommended to use expansion substrates with power supply (such as A1S65B, A1S68B) for independent power supply.

Common fault phenomena and troubleshooting

3.1 Fault 1: POWER LED not lit

This is the most common power failure, possible causes and troubleshooting process:

Step check content, normal status, abnormal handling

Is the input voltage normal? Check the external power supply, fuses, and circuit breakers for terminal voltage of 100-240 V AC

Is the input voltage selection terminal correct? A1S61PN did not select a terminal (wide voltage), but early A1S61P had a 100/200 V jumper to confirm that the jumper position was consistent with the power supply

Are the 3 modules fully inserted into the substrate? Tighten the fixing screw, clamp the hook, and reinstall

Is the output terminal short circuited? Unplug all load modules and test the power supply separately. If the LED lights up during separate testing, it indicates a short circuit in the load

Has overcurrent/overvoltage protection been triggered? If it still doesn't light up after powering off for 1 minute, the module is damaged and needs to be replaced

Special attention: The POWER LED of A1S61PN indicates that the 5V DC output is normal. If the LED does not light up but the input voltage is normal, 99% of it is internal damage to the module. During on-site emergency situations, modules of the same model can be temporarily replaced for testing.

3.2 Fault 2: System random reset or CPU stop

Phenomenon: PLC shuts down irregularly, CPU's RUN LED goes off or flashes.

Possible reasons:

Instantaneous power outage exceeding 20 ms: Check the stability of external power supply and whether there is a voltage drop caused by the start stop of large equipment.

Insufficient output capacity of power module: When there are a large number of I/O actions, the peak current of 5V exceeds the rated value, triggering overcurrent protection and causing a brief power outage.

Poor contact of extension cable: Vibration caused the extension cable to loosen, resulting in a momentary interruption of 5V power supply.

Solution:

Use an oscilloscope or recorder to monitor the 5V output waveform and confirm if there is any drop.

Recalculate the total current consumption, and if it approaches the upper limit, replace it with a larger capacity power module (such as replacing A1S61PN with A1S63P? But A1S63P is a 24 V DC input, please note).

Tighten all expansion cable connector screws and check for oxidation.

3.3 Fault 3: Abnormal 24V output (only A1S62PN)

A1S62PN provides 24 V DC 0.6 A auxiliary power supply, common faults:

No 24V output: Measure the voltage between terminals. If not, check if the overcurrent protection is activated (the 24V overcurrent protection point is 0.66 A). Disconnect all 24V loads. If the voltage returns, it indicates that the load is short circuited or overloaded.

Low voltage (<22 V): Excessive load current or module aging. Try gradually disconnecting the load and observing the voltage rise.

3.4 Fault 4: CPU running but I/O points not responding

This situation is often not due to a complete failure of the power module, but rather a fluctuation in one output causing abnormal communication on the I/O bus.

troubleshoot

Measure whether the 5V voltage is stable between 4.75 and 5.25V.

Check if the power pins on the substrate are oxidized or bent.

Use spare substrate for cross testing.

3.5 Fault 5: Error LED flashing during operation, special register reporting "FUSE BREAK OFF"

The manual points out that the FUSE BREAK OFF alarm does not necessarily refer to the internal fuse of the power module being blown, but rather to the external fuse of the output module's load being blown or the external 24V power supply being lost. But sometimes the abnormal 24V output of the power module can indirectly cause this alarm.

Inspection steps:

Read the status of special relay M9000 (fuse blown).

Check the special registers D9100 and D9101 to determine which output module has a problem with which set of points.

If all output modules report fuse breakage, it may be an open circuit at the 24V output common terminal of the power module.

Replacement and Upgrade of Power Modules

4.1 Identify discontinued models

Some power modules in the MELSEC AnS series have been discontinued, such as the A1S61P (switchable between 100/120 V or 200/240 V) which has been replaced by the A1S61PN (wide voltage). A1S61PN can still be purchased at present, but if it is not available, the following replacement strategies need to be considered.

4.2 Replacement Selection Comparison Table

Recommended Replacement Model for Prototype Number Output Specification Precautions

A1S61P 5 V 5 A, AC 100/200 V optional A1S61PN direct replacement, wide voltage input

A1S62P 5 V 3 A+24 V 0.6 A A1S62PN direct replacement

A1S63P 5 V 5 A, 24 V DC input has no direct replacement and needs to be replaced with A1S61PN+external 24 V to 100 V AC inverter, or other series

A1S61PEU 200-240 V AC, 5 V 5 A A1S61PN Please note that the PEU model has the CE mark, and the PN also complies with CE and can be replaced

A1S62PEU 200-240 V AC, 5 V 3 A+24 V 0.6 A A1S62PN Same as above

4.3 Replacement steps (on-site practice)

Power off: Turn off the main power supply of the system and confirm that all capacitors have been discharged.

Record wiring: The input terminals of the power module are usually L, N (or 1, 2), and the grounding is FG, LG. Take photos or mark.

Disassemble the original module: unscrew the two fixing screws on the top and bottom of the module, and remove the module.

Check the substrate: Clean the dust in the substrate slot and check if the pins are deformed.

Install new module: Align with the guide rail and push in, ensuring complete insertion, tighten the screws (torque 59-88 N · cm).

Reconnect: Connect the input power and ground according to the original markings.

Power on test: First disconnect all I/O loads, power on the PLC separately, observe that the POWER LED lights up and the CPU RUN is normal.

Restore load: Gradually connect the I/O power supply and monitor whether the 5V voltage is stable.

4.4 Alternative solution: Use third-party power supply

If the original A1S61PN cannot be obtained in a timely manner, a third-party switch power supply that meets the following conditions can be used as a substitute:

Output 5 V DC, current ≥ 5 A

The output voltage can be fine tuned (such as adjusting to 5.1 V to compensate for line loss)

Equipped with overcurrent and overvoltage protection

However, it should be noted that third-party power supplies cannot be directly inserted into the substrate, and additional adapter cables need to be made to introduce 5V into the power slot of the substrate. This requires professional knowledge and risk awareness, and it is not recommended for inexperienced personnel to operate. The best solution is to purchase spare parts from the original factory or legitimate channels.

System level fault prevention and maintenance

5.1 Daily Inspection (Daily)

According to Table 10.1 of the manual, focus on checking:

Is the POWER LED lit up normally

Is the substrate mounting screw loose

Is there any foreign object blocking the ventilation hole

Is the ambient temperature too high (not exceeding 55 ℃)

5.2 Regular maintenance (every 6 months to 1 year)

Inspection project method standards

Input voltage multimeter for measuring L-N terminal 85-264 V AC

The output voltage of 5 V is measured at the power pin of the CPU or I/O module, ranging from 4.75 to 5.25 V

24 V output voltage (A1S62PN) measurement 24 V terminal 21.6-26.4 V

Ground resistance measurement FG ground resistance ≤ 100 Ω

Manual inspection of module fastening shows no looseness

Dust cleaning using a vacuum cleaner or dry compressed air without significant dust accumulation

5.3 Battery and Data Retention

Although the battery (A6BAT) is not installed on the power module, but on the CPU module, power failure can cause the battery to deplete and accelerate. When the special relay M9006 (low battery voltage) or M9007 (low battery lock) is turned on, the battery should be replaced as soon as possible. When replacing, it is necessary to keep the power on or use a capacitor backup to avoid data loss.

EMC and low voltage command compliance

A1S61PN and A1S62PN are modules designed to meet the CE mark (see Appendix 4 of the manual), complying with the EN61010-1 safety standard and the EMC directives (EN50081-2, EN50082-2). Attention should be paid during on-site installation:

Grounding: FG (frame grounding) and LG (line grounding) must be grounded separately or short circuited before grounding. The grounding wire should be as short as possible (<30 cm).

Noise filtering: It is recommended to install a noise filter (such as SCHAFFNER FN343-3/01) at the power input end, and the input and output lines of the filter should not be tied together to prevent coupling.

Shielded cable: All I/O signal cables leading out of the control cabinet must use shielded cables, and the shielding layer must be grounded extensively inside the cabinet.

Fault case sharing

Case 1: Frequent PLC crashes in textile factory

On site: MELSEC AnS system, equipped with A1S61PN power supply, with a total load of 5 V and a current of approximately 4.2 A (close to the rated value). After running for a few hours, the PLC randomly shuts down and the POWER LED flashes before turning off.

Troubleshooting: Using a clamp meter to monitor the input current, it was found that the grid voltage dropped from 220 V to 190 V when the device was started. Although A1S61PN has a wide voltage, the instantaneous drop caused the internal switch power supply duty cycle to saturate, and the output overcurrent protection was activated.

Solution: Install a 2 kVA voltage regulator on the front-end and move some I/O modules to an independent power supply expansion board to distribute the load. Problem elimination.

Case 2: Chemical plant 24 V output without voltage

On site: The 24V output terminal of A1S62PN has no voltage, but 5V is normal. Upon checking the external load, it was discovered that a solenoid valve coil was short circuited, resulting in the triggering of 24V overcurrent protection.

Solution: Disconnect the short-circuit solenoid valve, cut off the power for 1 minute, then turn it back on and restore 24V. Suggest adding a self recovery fuse in the 24V output circuit.