Home > News > How to Solve Mitsubishi Alarm 25.1?

How to Solve Mitsubishi Alarm 25.1?

NOV. 11, 2025

Doing CNC maintenance of this line for a long time, a variety of servo alarms have seen more. Like Mitsubishi MDS-D, MDS-E series drive on the common 25.1 alarm, said trouble trouble - the machine suddenly stopped, the production line waiting for an emergency; but said that simple is also simple, as long as you understand the temperament of it, to solve the direction.

We Songwei side perennial contact with overseas customers Mitsubishi, Fanuc and other systems, from the supply of parts to the whole machine maintenance are done. Today do not talk about business, purely share some practical experience, talk about the 25.1 alarm in the end how to check, how to repair.

What exactly is a 25.1 alarm?

Simply put, 25.1 is the main circuit voltage is too low. You can think of the drive's internal DC bus as a "reservoir”, it should be maintained at a certain level during normal operation (for example, 200V class system is usually around 270-310VDC). Once the voltage falls below the safety line (about 250VDC or less), the drive triggers protection, report 25.1.

This alarm is really the drive screaming, "I don't have enough power to spin!” It is not a garbled alarm, but there is actually a voltage problem.

What causes 25.1?

According to the cases we have repaired, the problem usually lies in the following blocks:

① External power supply problem

- Unstable or low three-phase voltage in the workshop (e.g. more than 10% below the rated value)

- Loose or oxidized power supply terminals, resulting in high contact resistance

- Transformer or distribution box capacity is not enough, a load on the voltage down

② Internal aging or damage to the driver **

- DC capacitor aging: the most common reason! Electrolytic capacitors with five or six years will slowly "weak”, capacity decline, internal resistance becomes large, can not store electricity!

- Rectifier module / IGBT failure: responsible for charging the power components are bad, the DC bus simply can not be charged!

- Voltage detection circuit problem: obviously normal voltage, but the detection circuit misjudged as low voltage

③ Abnormalities of the motor and load

- Sudden mechanical jamming, excessive load, the voltage is instantly pulled down as soon as the motor is started

- The insulation of motor cable is broken, short circuit to ground, resulting in leakage

④ Environment and installation factors

- Poor heat dissipation in the cabinet, high temperature accelerates the aging of capacitors

- Poor grounding or voltage shocks in the power grid

Hands-on troubleshooting process

Note: Be sure to disconnect the power before operation, and wait for the drive indicator light to go out before doing it, safety first!

Step 1: Don't rush to reset first

Record the timing of the alarm: is it reported on power-up? Or is it occasionally reported during operation? Is there an accompanying strange noise or burning odor? This information is important

Step 2: Check the supply voltage

- Energized (without load), use a multimeter to measure the three-phase voltage of the R, S, T terminals of the driver

- See if it is within the range of 200-230V±10% and if there is any serious imbalance

Step 3: Measure the DC bus voltage

- Find the P (+) and N (-) terminals inside the drive and measure the DC voltage

- Normal should be about 270-310VDC, if lower than 250VDC or even lower, then the problem is obvious!

Step 4: focus on checking the capacitance

- Open the drive to see if the capacitor has "bulging”, ‘leakage’, "top bulge”

- Conditional capacitance meter to measure the capacity and ESR (equivalent series resistance), aging capacitors are usually reduced capacity, ESR rises

Step 5: Check the power components

- If the DC voltage never comes up, disconnect the motor wires and try again. If it is still low, it is likely that the rectifier module is bad

- Check U/V/W for short circuit to ground

Step 6: Checking the detection circuit

- Use Mitsubishi's MR Configurator software to read the DC voltage value displayed by the driver and whether it is consistent with what you actually measured

- If the software display value is much lower than the actual value, then the detection circuit is likely to be faulty

Step 7: Check the motor and mechanical

- Measure the insulation resistance of the motor (should be ≥ 1MΩ)

- Manually rotate the screw or belt to see if it is smooth and there is no jamming

Step 8: After repairing the verification

- After repairing, first test run with no load, and then slowly add loads

- It is best to run under simulated production conditions for a period of time to confirm that the alarm no longer occurs

A few common mistakes made by newbies

- Trying to reset the alarms: this is the most important thing to do, and it may turn a small problem into a big problem

- Blindly changing boards: changing motherboards and driver boards without identifying the problem is a waste of money and does not solve the problem

- Neglect the voltage fluctuations in the workshop: especially the alarm caused by the voltage drop during peak hours of electricity consumption

- Don't pay attention to the life of capacitors: capacitors are consumables and should be replaced when the time comes, don't wait for it to completely break down

Repair or replace? Look at these points

Suggested Repair:

- The problem is clear, such as one or two bad capacitors, rectifier diode burned

- The parts are easy to find, and the repair cost is much lower than buying a new one

- You have your own test conditions, can be repaired on the machine verification

Recommended for replacement of the situation:

- Power module repeatedly bad, fixed here bad there

- Driver model is too old, parts can not be found

- The production line is particularly critical, the loss of one hour of downtime is more expensive than the drive itself

We Songwei repair drive, repair will be on the test bench full load verification, to ensure that the product out of the stability and reliability.

Prevention is better than cure: a few maintenance suggestions

- Regularly measure the voltage: record the AC input and DC bus voltage once a quarter, so that you have a clear idea of what is going on

- Capacitors should be replaced on time: 5-7 years for normal environment, 3-5 years for high temperature and high load environment

- Keep the cabinet clean and ventilated: dust and high temperature is the enemy of electronic components

- The unstable voltage workshop with a voltage regulator: spend a small amount of money to save a lot of trouble

- Check motor cables often: see if there is any broken skin, loose joints

Do a good job of preventive maintenance, 25.1 this kind of alarm will be much less.

Why call us?

Although this article is purely technical sharing, if you need professional support, we at Songwei can provide:

- Original, used and refurbished Mitsubishi drives, flexible to meet budgets and lead times

- Specialized Mitsubishi test bench, capable of simulating DC bus voltage changes, load testing, accurate reproduction of 25.1 alarms

- Worldwide delivery, reducing equipment downtime

When you encounter 25.1 alarms that can't be solved, finding a reliable partner can save you a lot of heartache.

The last few words

Mitsubishi 25.1 alarm is annoying, but as long as you follow the order of "from the outside to the inside, from the simple to the complex” investigation, most of the cases can be solved. The key is not to panic, step by step: first confirm the power supply, and then check the capacitance and power components, and finally look at the motor and load.

Usually do a good job of maintenance, encounter problems with scientific overhaul, your CNC equipment will be able to run steadily for a longer period of time. If you need professional maintenance and testing services, we at Songwei are always ready to support you.

Related Product Types

If you found this article interesting, you may want to know more about these related product types.

Contact Us to Maximize Your Profit

Enter part information below to check price and availability.

Usually ship by UPS or DHL with delivery around 3 working days.

All parts are tested OK before shipping out with a 12-month warranty.

Provide technology guidance service upon receiving the part.

Input

Feedback *

Enter Verification Code:*

I accept the SongWei CNC Privacy Policy

CONTACT US

Thank you! Your message has been sent.

Unable to send your message. Please fix errors then try again.

How to Solve Mitsubishi Alarm 25.1?

The last few words

Related Product Types

Search