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

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