Category: service

Posted on by — Leave a comment

Why should we add an input reactor to the fragile small power VFDs

A factory has a 5.5 kW submersible pump. To facilitate water volume adjustment and energy-saving operation, an electrician proposed using a VFD to drive the pump.

The task was taken on by Mr. Zhang, a friend of the electrician. For safety, Mr. Zhang selected a 7.5 kW VFD from a reputable brand. This brand’s VFDs are widely used in various industries such as plastics, chemicals, and wood processing without significant issues, indicating decent quality. The VFD control box was installed in the boiler room, with power sourced from the workshop distribution panel. The three-phase voltage balance was excellent, maintaining within 380V ±5%. During the trial run, the VFD did not need to operate at full speed, running around 30Hz with the working current at half of the VFD’s rated current. Mr. Zhang was confident that the VFD would operate safely for a long time.

However, three days later, the factory’s electrician called Mr. Zhang, reporting that the VFD had stopped, and the control panel was unresponsive, indicating no power. Surprised, Mr. Zhang visited the site and confirmed the issue. Assuming a quality problem with the VFD, he replaced it with another 7.5 kW VFD from the supplier and sent the defective one for repair.

This time, the VFD failed after just a day and a half. Frustrated, Mr. Zhang called the supplier to complain and replaced the VFD with another brand. He again checked the operating voltage and current, which were similar to the initial installation, indicating no issues with the pump or power supply. Mr. Zhang concluded that the first batch of VFDs might have had quality defects and hoped the new brand would solve the problem.

Unexpectedly, the newly installed VFD also failed within hours, with the factory’s electrician calling Mr. Zhang again. The recurring issue led to reprimands from the factory boss to the electrician, who then passed the blame to Mr. Zhang. Baffled, Mr. Zhang inspected the three faulty VFDs. He found that two had open circuits between the R and P1 (external brake resistor terminal), possibly due to damaged charging resistors, which indicated rectifier circuit issues. The third VFD had a short circuit between R and S, suggesting a failed rectifier module. However, the inverter modules in all three VFDs were intact. The damages seemed to result from power surges, not load-related issues, as the three-phase supply voltage and input current were normal. Having worked with VFDs for several years, Mr. Zhang found this problem unprecedented.

In desperation, Mr. Zhang called his friend, electrician Mr. Li, for advice. Mr. Li suggested installing a three-phase input reactor before the VFD’s power terminals to solve the problem.

Mr. Zhang inquired about the cause of the failures. Mr. Li explained three potential reasons related to the power supply:

1. The submersible pump continued to operate after work hours for employee showers, meaning a 630 kVA transformer supplied a 7.5 kW VFD, causing a significant capacity disparity. The VFD’s input current contained high harmonic components, generating large rectifier inrush currents that damaged the rectifier module and charging resistor during startup.

2. The workshop distribution panel might have parallel capacitor compensation cabinets. The start and stop of large motors (above 100 kW) and the switching currents of capacitors created harmful voltage spikes and inrush currents, impacting the VFD.

3. The same power line might have other large VFDs, soft starters, or DC speed controllers. The nonlinear rectifier currents from these devices severely distorted the power supply waveform, increasing harmful harmonics and deteriorating power quality.

Mr. Li noted that input reactors, often depicted in VFD wiring diagrams, are frequently omitted during installation to save costs, leading to such issues.

Mr. Zhang didn’t have ready-made three-phase reactors and needed an immediate solution. Mr. Li suggested using XD1 series chokes from old capacitor compensation cabinets as reactors, which could suppress inrush currents effectively. Mr. Zhang contacted several suppliers but learned that most manufacturers had stopped producing these chokes.

Under pressure, Mr. Zhang reached out to Mr. Li again, demanding a solution. Mr. Li, while having lunch, suggested using current transformers (CTs), which Mr. Zhang likely had. Any CT, regardless of size, with a rated current of 5A, could be used. CTs with more winding turns (e.g., 50/5) would offer better inrush current suppression and filtering but might have a higher voltage drop. Conversely, CTs with fewer turns (e.g., 250/5) would have a smaller voltage drop but less effective smoothing. Depending on the VFD’s rated current, Mr. Li recommended using three CTs per phase or two if the running current was around 7A. CTs would provide better inductance and performance than XD1 chokes.

After installing CT-based “input reactors,” the VFD’s input current became stable, reducing harmonics and voltage spikes, ensuring safer operation.

Months later, Mr. Zhang checked with the factory electrician, who confirmed that the VFD had been operating normally. Mr. Zhang realized the VFD failures were due to power supply issues, not the VFD quality. He felt vindicated and teased the electrician about owing him a drink for resolving the issue.

Posted on by — Leave a comment

The repair process of an unlicensed VFD caught up with lightning speed

In movies and TV shows, when a Taoist from Maoshan encounters an urgent and difficult situation, he often recites a curse: “The Supreme Old Lord is as sick as a law… If something difficult happens, it should be solved by the curse.”. If there is an urgent VFD repair, we can also recite a few mantras and find the “smart” method for quick maintenance.
On a rainy day, thunder and lightning flash. The door of the maintenance department was suddenly forcefully pulled open by someone. Three or four strong men, carrying an unmarked 75kW VFD, strode in and asked, “Our workshop is for refining silver, and the frequency converter was damaged by lightning.”. Urgent use! Can the malfunction be detected and repaired within three hours. Okay, don’t bargain; If you don’t have diamond, don’t take on porcelain work. Let’s quickly change the door. It’s not just you who can fix VFD.
This VFD may be able to earn half a month’s salary. No second words, fight!

I roughly inquired about the damage to VFD. During operation, due to lightning strikes introduced from the three-phase power supply, even the main power switch in the workshop tripped. Close the power switch of VFD again, there is a popping sound, and the switch jumps open again.
In this situation, there must be a short circuit fault in the three-phase rectifier circuit of VFD. Instead of being busy with power on, use the resistance range of the multimeter’s R, S, T power input terminals and U, V, W output terminals to determine the resistance of the main circuit with the P and N terminals of the DC circuit. There is a short circuit phenomenon in the measurement, rectification, and inverter power circuits. Detailed inspection after disassembly revealed that two rectifier modules were damaged, one inverter module was broken, and the energy storage capacitor was tested and found to be fine.
The repairman asked, “Isn’t it enough to replace these three faulty parts?”? Answer: Don’t be impatient. Due to the introduction of lightning strikes within VFD, the situation is complex and the quality of the control circuit board is unclear. If the inverter power module is damaged, it will have an impact on the driving circuit. If there is a hidden fault, the replacement module will be damaged again. Further investigation is needed to determine whether to replace the module.
Key contents to be checked: 1. Whether the CPU motherboard is damaged, especially whether the CPU chip is damaged; 2. Inverter pulse transmission circuit, including driving circuit and inverter pulse front-end circuit. Especially for the driving circuit, the triggering terminal circuit of the IGBT should be checked for any open circuit or negative pressure power supply; 3. Other circuits, whether the control terminal circuit has been damaged by lightning strikes, and whether the control circuit (fault detection circuit, etc.) has been damaged.
The key among them is that as long as the CPU can output six inverter pulses, repairing other faults should be easy.

(A) Power on the switch power supply or troubleshoot the switch power supply:
Remove the CPU motherboard and power/driver board from the inverter casing and place them on the maintenance workbench. Power should be supplied to the switch power supply of the circuit board first, or the switch power supply should be repaired first to facilitate troubleshooting of other circuits. I tested the power supply terminals of the switching power supply and the filtering capacitor at both ends of the secondary rectification circuit of the switching transformer, and there was no short circuit phenomenon. It is possible to power on the switching power supply. The power supply source of the Shunxia switch power supply is directly taken from the 530V DC circuit of the DC circuit. If measured on the circuit, the drain (collector) of the switching transistor of the switching power supply should be connected to the P-terminal of the DC circuit, and the source (emitter) should be connected to the N-terminal of the DC circuit.
Alright, connect the 500V DC maintenance power supply to the power supply terminal of the switch mode power supply (pay attention to polarity, it can be bad if connected in the opposite direction), it’s not bad! The corresponding changes in characters during the startup period on the operation display panel indicate that the switch power supply and the peripheral circuit of the CPU chip are basically working normally, and the CPU is also good.
(B) Release the OH (module overheating) fault alarm:
After the startup character on the operation display panel flashes, an OH (module overheat) fault code is reported. Press the RST reset button on the operation display panel, OH disappears once, and it is displayed again, unable to reset. At this time, the frequency converter is in a fault locked state and refuses to accept operating signals, making it impossible to detect whether the inverter pulse transmission circuit is normal. The OH alarm must be disarmed. Observing the main circuit, two normally closed contact type thermal relays are installed near the heat sink module. When the circuit board is disconnected from the main circuit, it is equivalent to the temperature sensor’s normally closed point breaking, reporting an overheat signal. Find the corresponding temperature sensor terminals on the circuit board, short circuit them with wires or solder, and there should be no OH fault reported. Some frequency converters use thermistors to detect the temperature of the module. When the terminal is open, an OH fault will also be reported. Simply remove the temperature sensor and insert it into the corresponding terminal on the control board. Still report OH, don’t worry, there may be related temperature detection signals sent to the control board.
Observe the socket and lead of the cooling fan, which is a three wire fan. Two wires are the positive and negative terminals of the 24V power supply, and one wire is the signal wire. Return the operation/fault signal to the control board. If you remove the fan and plug it back into the control board, it would be too troublesome. There is a simple way to find the positive and negative wires, and test connecting the third wire to the positive and negative power supply terminals respectively. When this wire is connected to the positive power supply terminal, the OH fault code on the operation display panel disappears.
(C) Release Uu (undervoltage) and input phase loss alarm:
After a brief moment of joy, the operation display panel showed another Uu (undervoltage) fault, and the frequency converter was still in a fault locked state.
When the switching power supply adopts 265V (or 300V) DC power supply, we disconnect the control board from the main circuit and separately supply 265V (or 300V) DC power to the switching power supply. Most of the operation panels will report Uu faults (some frequency converters, DC circuit voltage detection signals are obtained in the secondary rectification circuit of the switching transformer, so Uu faults will not be reported), because the input of the DC circuit detection circuit is in an open circuit state, and the circuit output is an undervoltage signal. From the DC circuit voltage introduction terminals (P, N terminals), find the input resistance network of the DC circuit detection circuit, a large high resistance circuit, seven or eight phases in series, because the switching power supply is 300V DC power supply at this time, directly introduce it into the DC circuit voltage detection circuit, or report a Uu fault. Short circuit a few resistors in the input resistor network (if there are 8 resistors, 3 can be short circuited for testing) to adapt to the 300V voltage output range.
Introduce a DC voltage artificially into the DC detection circuit and modify the detection to meet the requirements of the voltage input range. Some frequency converters may not report Uu faults, but they may also report “charging contactor not engaged fault”, while others may still report Uu faults. Don’t worry, there may be related voltage detection signals sent to the control board.
The charging contactor cannot be removed and connected to the control board in the main circuit. The frequency converter often has a status detection circuit for the auxiliary contact of the charging contactor. Due to the disconnection between the control board and the main circuit, the CPU detects that the auxiliary contact of the charging contactor is always in an open circuit state after the control board is powered on, and will also report Uu or “charging contactor not engaged fault”. Find the lead terminals of the auxiliary contacts of the charging contactor from the main circuit, determine the corresponding socket terminals of the control board, short circuit or solder the lead terminals with wires, and tell the CPU that the charging contactor has been closed.
After short circuiting the lead terminals of the auxiliary contacts of the charging contactor, the operation display panel finally stopped tripping Uu fault.
(D) Release OC (module overcurrent or output short circuit) fault alarm:
After a brief moment of joy, the fault code no longer jumps. From the display on the operation display panel, it appears that the inverter has entered standby mode and can be started for maintenance of the inverter pulse transmission channel. Press the start/stop button on the operation display board, but the frequency converter does not respond. The user may have set it to terminal operation. Ask the repairman, and indeed. For the convenience of operation, if the control parameters can be modified (if there is a frequency converter manual at hand), or the operation can be changed to start/stop and frequency adjustment using the control panel; If it is inconvenient to modify the parameters, you can try inputting the operation and frequency signals from the control terminal. Measure the frequency and adjust the power supply to 10V for normal output. Short circuit it to the input end of the 0-10V frequency signal to input the highest operating frequency command for the frequency converter (it is not troublesome, but can also be adjusted with an external potentiometer). Short circuit the forward running terminal to the digital common terminal for a startup test, and the operation display panel will display an OC fault code. Of course, the frequency converter is still in a fault locked state and cannot accept the operation.
The power module cannot function without various comprehensive protections, but at this point, I really feel that these fault alarms are troublesome. However, if they are not resolved, the inverter pulse transmission circuit cannot be repaired. Slowly, when an alarm signal is issued, it will be tracked and released. Generally, when the control circuit board is disconnected from the main circuit, three or four faults will jump out. Pay attention to finding the source of each signal from each plug-in terminal, or from the input and output sides of the plug-in terminal or the optocoupler that transmits the signal, use wire short circuiting method to force the CPU to input a “normal” signal and release the fault lock state.
The OC signal is mostly sent back to the CPU by the IGBT voltage drop detection circuit (IGBT protection circuit) of the driving circuit. When there is a fault in the output current detection circuit, an OC fault will also be reported, but this situation is relatively rare. Following the principle of easy first and difficult later, the OC signal returned by the driving circuit can be released first, and then the output current detection circuit can be detected.
The commonly used ICs for driving circuits are PC923, PC929, and A316J. The former uses the OC signal output by the internal IGBT protection circuit of PC929, which is then sent to the CPU through an external optocoupler. Find the optocoupler connected in parallel with PC929, and short-circuit its input side with a soldering iron to release the OC alarm (it is a fast method, not a good method); The latter, the 5 pins of the driver chip A316J are the OC signal output pins, which are separated from the copper foil strip to isolate the transmission of OC signals; But this method is not very convenient. Although it blocks the transmission of OC signals, it is advisable to check whether the CPU and the front-end inverter pulse transmission circuit have output inverter pulse signals. However, the drive IC itself is still in a fault locked state, which is not conducive to repairing the drive circuit.
A good solution is to manually input an IGBT “normally open” signal to the IBGT detection circuit, so that the driving IC itself no longer reports OC faults during the input inverter pulse period. The general driving circuit is implemented by the lower three arm driving circuit to detect the voltage drop of the IGBT transistor. The trigger terminal is used to short circuit the output end of the inverter pulse to the OV end of the driving power supply (the connection point with the N end of the main circuit), which is also relatively easy to find.
(E) Perform maintenance on the drive circuit:
Finally, the frequency converter can accept the startup signal. Looking at the gradually increasing output frequency indicator displayed on the control panel, I breathed a sigh of relief, indicating that the CPU circuit and control terminal circuit are both good. The repair of the frequency converter is basically without any suspense.
Measure the six inverter pulse input terminals of the driving IC, and there is a significant voltage change in the start and stop states. The six inverter pulses from the CPU motherboard have been input into the driving circuit intact and undamaged. The CPU motherboard is good! Measure the output status of six inverter pulses from the pulse output terminals of the power/driver board, and check if the negative cutoff voltage is normal and if there are normal pulse outputs. Does the voltage amplitude and current amplitude of the pulse output meet the normal requirements? Due to the damage of the IGBT causing impact on the driving IC, there are two driving circuits that cannot output pulse signals normally. This is simple. A power amplifier consisting of a driver IC and a rear stage consisting of two transistors was found to have damaged components. After replacement, all six inverter pulses were output normally.
The maintenance process has been declared completed. The entire maintenance process took exactly 45 minutes. After the maintenance is completed, it seems like we won a small battle so happily. The next task is to replace and purchase modules.

Throughout the entire maintenance process, four strong men were eagerly staring at the frequency converter, including one electrician who was extremely excited: he had learned and really had real skills. I didn’t expect it to be so troublesome. Blowing up a module is not as simple as replacing it.
To the repairman, the control circuit has been repaired, but there is no power module at hand. Then, you can go to the same city to “search” for it. If not, it will only be sent from outside the city. You will have to find your own way to delay your silver refining.
The four repairmen all laughed and said, “No problem, no problem. Please hurry up and send the package.”.
The various methods used during the maintenance process are scattered in my other blog posts, but they belong to local maintenance methods. For actual maintenance, sometimes there is a small gap between what is explained by a single unit circuit, which is difficult to understand. Through the description of a specific maintenance example process in this article, the application of various maintenance methods can be integrated and integrated.

Posted on by — Leave a comment

High price cash recovery: used automation /engineering surplus materials

Cash high price recycling of various industrial control products. If you have inventory, second-hand, or engineering surplus industrial control products, such as VFDs, PLCs, touch screens, servo systems, CNC systems, robots, instruments, sensors, control panels, etc., regardless of quality or old, you can resell them to us, allowing them to be monetized in a timely manner and accelerating your capital recovery.

Since its opening, Longi Electromechanical has a development history of more than 20 years. The company adheres to the principle of “integrity-based, fair dealing between children and the elderly, and fair and conscientious management”, and takes every transaction seriously.

The procurement process follows the principles of “offering the best price”, “not letting partners suffer losses”, “confidentiality and security”, “fast and convenient”, “cash payment”, etc., to ensure that partners can trade with confidence.

With rich industry experience, we can quickly estimate a reasonable acquisition price online through the pictures or videos provided by our partners. After negotiating the price, transactions can be made through logistics collection, online payment, or face-to-face transactions.

Posted on by — Leave a comment

Global Ultrasonic Equipment Maintenance Center

Longi Electromechanical Company uses artificial intelligence AI methods and professional technical teams to professionally repair various types of ultrasonic equipment. It can achieve component level maintenance and repair general problems on the same day, winning valuable time for customer production. There are many types and brands of ultrasonic equipment devices, and currently there are a large number of ultrasonic equipment in the market, with varying quality and old and new. Rongji Electromechanical Company has repaired over 2000 related equipment and accumulated rich maintenance experience.Phone/WhatsApp:+8618028667265

Longi has excellent mechanical and electrical technology, and has great confidence in its repair level. The repaired ultrasonic welding equipment has a one-year warranty for the same problem point. The maintenance cost is relatively low, and the price is lower than the peers.

Longi Electromechanical repairs several types of ultrasonic equipment, including:

Plastic hot plate welding machines, ultrasonic welding machines, high-frequency welding machine maintenance, hot melt hot plate welding machines, multi-head ultrasonic welding machines, ultrasonic plastic welding machines, ultrasonic fusion welding machines, ultrasonic spot welding machines, hot plate welding machines, and hot melt welding machines.

Ultrasonic metal welding machines, ultrasonic metal spot welding machines, ultrasonic metal wire welding machines, ultrasonic metal roll welding machines, solar collector plate welding machines, solar copper pipe punching machines, and copper pipe flanging machines.

Automotive door panel welding machines, automotive interior part welding machines, automotive instrument panel welding machines, automotive bumper welding machines, automotive radiator welding machines, and automotive light welding machines.

Ultrasonic flaw detectors, ultrasonic welding and cutting machines, ultrasonic food cutting machines, ultrasonic tool heads, ultrasonic cutting knives, ultrasonic cake cutting machines, handheld ultrasonic welding machines, ultrasonic cleaners, KN95 mask sealing machines, semi-automatic spot welding machines for flat masks, manual mask spot welding machines, N95 mask earloop ultrasonic welding machines, ultrasonic mask sealing machines, automatic frequency tracking ultrasonic welding machines, handheld ultrasonic spot welding machines, and fully automatic ultrasonic welding machines.

Ultrasonic vibrating plates, ultrasonic power boards, ultrasonic transducers, ultrasonic generators, presses, ultrasonic boosters, ultrasonic welding heads, and supporting tooling.

Rongji Electromechanical has extensive experience in repairing and maintaining this diverse range of ultrasonic equipment, ensuring that these machines continue to operate at peak performance.

Longi Electromechanical has repaired ultrasonic equipment from various brands, including:

Minghe, Changrong, Swiss RINCO, Dingtaihengsheng, Gute, Xinzhi, Taiheda, Donghua, Ruang, American Branson, Daguangdian, Swiss TELSONIC, German SCHUNK, American AMTECH and SONICS, Korean TECHSONIC, Chuxin (SONICTECH), Jiemeng, Jikang, Hekeda, Kejiemeng, Weigute, Meiji, Fukeda, Jieda, and Haoshun.

The company’s experienced engineers are familiar with the repair and maintenance requirements of these brands, ensuring that the ultrasonic equipment is restored to its optimal performance. Rongji Electromechanical’s expertise in repairing a wide range of ultrasonic equipment brands demonstrates its versatility and reliability in the industry.

Over the years of repairing ultrasonic equipment, we have identified the following common faults:

The cleaning water surface does not vibrate, and there is debonding between the vibrator and the load.
The mold head is misaligned.
There is no display when turned on, and there is an overload or overcurrent during the welding process.
The current is too high during testing.
Insufficient welding capacity during the welding process, or the welding heat is too intense.
The vibrator has leakage waves.
The button does not work when pressed.
There is an issue with the travel protection.
There is sound, but the power cannot be adjusted.
The ultrasonic intensity is insufficient.
The transducer ceramic is cracked.
The power tube is burned out.
The voltage stabilization part is not functioning properly.
There are problems with the inductor and isolation transformer.
The vibrator wire is disconnected.
These faults can occur due to various reasons such as wear and tear, improper use, or component failures. It is important to regularly inspect and maintain ultrasonic equipment to identify and address these issues promptly. Our team of experienced engineers at Rongji Electromechanical is well-versed in diagnosing and repairing these common faults, ensuring that your ultrasonic equipment is restored to its optimal performance.

Principles for Ultrasonic Equipment Repair:

  1. Observe first, understand next, and then act, from the outside in.

When encountering problems with ultrasonic equipment, one should not blindly continue operating or rush to take action. It is essential to first inquire with the frontline production staff on duty that day to understand clearly when the problem occurred and the actual fault situation. Check if there were any voltage fluctuations, thunderstorms, or unauthorized disassembly at the scene.

If there is no response from the equipment, it is likely that a fuse or short circuit has occurred. In this case, focus on checking the electrical situation and measuring impedance with a multimeter. For unfamiliar ultrasonic equipment, do not dismantle it immediately. It is necessary to research its structure and related manuals online. When disassembling, pay attention to the coordination process of each part, keep the parts organized, and label anything that needs to be remembered. If necessary, draw simple diagrams. Acting rashly may escalate the problem or even make it impossible to reassemble the equipment.

  1. Simple before complex

Start by ruling out peripheral issues. Factors such as the surrounding environment, electricity, load, raw materials, and molds can all affect the normal operation of the equipment. First, confirm whether these aspects are functioning properly. Clean the equipment and its environment, as this sometimes resolves the issue. For example, oil and dust on some buttons can cause poor contact. If possible, swap two ultrasonic devices or other components for comparison to confirm the problem’s general direction. Only after confirming that the ultrasonic device itself is the issue should you disassemble it or send it out for repair.

For equipment that has had problems in the past, there is a high likelihood of similar failures recurring, so pay close attention to these areas.

  1. Address mechanical issues first

Mechanical problems can be seen with the naked eye, such as issues with the mold. Even if the transducer is working, the equipment may not function properly, which can be determined through touch and comparison. If mechanical problems are not addressed and one blindly searches for electrical causes, it will be like looking for a needle in a haystack and will never be resolved. Admittedly, dealing with mechanical issues can be somewhat challenging, but they must be resolved.

Posted on by — Leave a comment

Global Instrument Maintenance Center

Intelligent Precision Instrument Maintenance Base，Professional maintenance of various intelligent instruments and meters, phone/WhatsApp:+8618028667265, Mr. Guo

Longi Electromechanical specializes in repairing various imported intelligent precision instruments and meters, and has accumulated rich maintenance experience over the years, especially environmental testing instruments, electrical instruments, thermal instruments, acoustic and flow instruments, and electrical instruments. Environmental testing instruments, thermal instruments, acoustic and flow instruments,
We can quickly repair radio instruments, length instruments, environmental testing equipment, quality inspection instruments, etc.
Different instruments have different characteristics and functions, and their circuits and structures are also different. Even for the same instrument, if there are different faults, repairing them is still a different solution. Rongji Company has numerous high-end maintenance engineers equipped with artificial intelligence AI detection instruments, which can provide you with multi-dimensional solutions to various tricky instrument problems.

Over the years, Longi Electromechanical has repaired instruments including but not limited to:

Spectrum analyzers, network analyzers, integrated test instruments, 3D laser scanners, noise figure testers, receivers, telephone testers, high and low-frequency signal sources, audio and video signal analyzers, constant temperature and humidity chambers, thermal shock chambers, simulated transport vibration tables, mechanical vibration tables, AC grounding impedance safety testers, safety comprehensive analyzers, withstand voltage testers, battery internal resistance testers, high-precision multimeters, precision analyzers, gas and liquid analyzers, metal detectors, LCR digital bridges, oscilloscopes, electronic loads, power meters, power analyzers, multimeters, DC power supplies, AC power supplies, CNC power supplies, variable frequency power supplies, and various communication power supplies.

We have repaired the following brands:

Chroma, ITECH, Tonghui, Agilent, Tektronix, Keysight, Fluke, Keithley, Rohde & Schwarz, Lecroy, Anritsu, Rigol, and many more.

Longi Electromechanical strives to provide comprehensive repair services for a wide range of instruments and equipment, ensuring that our customers’ devices are restored to optimal performance.

Longi maintenance engineers possess over twenty years of experience in instrument repair. We have multiple engineers who excel in repairing imported precision instruments. The team works together, enabling faster troubleshooting and quick resolution of complex issues while improving the repair rate of instruments.

Spare parts are fundamental to successful repairs. Many imported instruments and meters require specialized components that cannot be easily replaced with generic market parts. Rongji Electromechanical maintains a long-term stock of electronic components for various instruments, ensuring their availability when needed.

Documentation and manuals are also crucial tools for ensuring rapid repairs. Accessing these resources allows for quick research and analysis of faults, enabling engineers to quickly identify the repair priorities. Longi Electromechanical has a long history of collecting specifications for various brands and models of instruments, greatly aiding in the repair process.

The intelligent instruments that have been carefully repaired by us can generally continue to be used for about 5 years. We promise that when the same malfunction occurs again, our repair service will provide a one-year warranty service.

Posted on by — Leave a comment

Global Touch Screen Repair Centers,Professional maintenance touch screen

Touch screen is a special human-machine dialogue device that has been widely used in daily life, production, and commercial occasions. Touch screens are mainly divided into several forms: resistive screens, capacitive screens, infrared screens, and ultrasonic screens. Because it has too close contact with people and a large part of it is a vitreous structure, the probability of touch screen damage is relatively high. The most common area of damage to touch screens is often the surface touch outer screen, commonly known as the “touchpad,” which can be used normally after replacement.
Rongji Electromechanical Maintenance has been using touch screens in the industrial, commercial, medical, and military fields for over 20 years. Currently, in these areas, resistance screens are mostly used due to reliability and safety considerations. The automotive industry uses both resistive and capacitive screens, and touch screens in this field, whether they are capacitive or resistive, can be repaired by us.

Step 1: Remove the back cover and remove the motherboard screws

Touch screen manufacturers, considering profit, often design touch panels and even LCD components as non-standard products, and do not disclose the drivers and circuits to the public. If standard touch panels and controllers are installed, they are often not compatible.

Step 2: Remove the outer shell and use a hair dryer to heat up the film

Longi Electromechanical Company has a team of engineers who have been researching the reverse engineering of various touch screens for a long time. They have explored a solution and replacement process for touch screen accessories from the bottom layer or touch panel technology. They can perfectly use the touch panel and other accessories produced by Longi Company to replace the original ones, and solve problems for customers while significantly reducing maintenance costs.

Step 3: Peel off the film and remove the touchpad

Most resistive screens and a small portion of capacitive screens can be purchased from touch pads produced by Longi Company. Following the replacement method we provide, they can be installed and used normally.

Step 4: Apply double-sided tape to the touch screen border and place a new touch pad on it

A small number of resistive screens and some capacitive screens, due to their special design, customers can send the entire touch screen to Rongji Company by mail. We use professional software analysis and judgment, and through hardware processing and software patching methods, we can achieve cracking and replacement.

Step 5: Install the motherboard LCD and flip it over to test if the touchpad is functioning properly

Similarly, for accessories such as LCD, high-voltage bars, and light tubes, similar methods can be used to achieve functional repair of touch screens without affecting their use.

Step 6: After successful testing, apply the film and replace the touchpad

During the use of touch screens, in addition to the mentioned accessory issues, there may also be circuit failures such as power boards or motherboards. For example, it is not displayed, or the display is abnormal. This situation belongs to a hardware malfunction of the circuit. The entire machine can be sent to the headquarters of Longi Company by mail, and we will use circuit maintenance methods for repair.

A special situation is when there is a problem with the touch screen software, such as the battery running out or data being lost. This situation is quite troublesome. If the customer has backed up data, we can help them re-enter it and it can be used normally. If the customer does not have backup data and cannot contact the equipment manufacturer to find the data, the only solution is to rewrite the appropriate touch screen program according to the process and equipment flow. As touch screens are secondary development applications, the programming difficulty is not too high. However, it will take time to pair with other devices in the system, such as PLCs.

Longi Electromechanical Company has repaired the following brands of touch screens:

Siemens touch screens, Proface touch screens, Mitsubishi touch screens, Fuji touch screens, Panasonic touch screens, OMRON touch screens, WEINVIEW touch screens, Koyo touch screens, Delta touch screens, Toyota JAT touch screens for air-jet looms, Staubli touch screens, Beijer touch screens, AB (Allen-Bradley) Rockwell touch screens, Hitech touch screens, Schneider touch screens, Toyo touch screens, DMC touch screens, MCGS (Kunlun Tongtai) touch screens, Touchwin touch screens, General touch screens, Red Lion touch screens, B&R (Beckhoff & Rautert) touch screens, LG touch screens, M21 touch screens, Fatek (Yonghong) touch screens, IDEC (Waizu) touch screens, Wecon touch screens, Pingtong touch screens, Fanuc touch screens, Lenze touch screens, Advantech touch screens, Hakko touch screens, Yushin touch screens, UNIOP touch screens, Shihlin (See) touch screens, Parker touch screens, Eura touch screens, and Hakko White Light touch screens, among others.

Please note that some of the brand names mentioned may be trademarks or registered trademarks of their respective companies. The listing here is for informational purposes only and does not imply any affiliation or endorsement by Longi Electromechanical Company or any of the mentioned brands.

Common Touch Screen Issues:

Display is visible but cannot be touched or clicked, or the touch response is poor. In most cases, this is due to a faulty touch panel. Sometimes recalibrating can solve the problem, but mostly the touch panel needs to be replaced.

The touch screen does not display anything, and even the indicator lights are not on. This situation usually indicates a problem with the power supply unit of the touch screen.

The touch screen functions but displays a black screen, while the indicator lights are normal. This is typically caused by a burned-out backlight tube inside the screen.

The touch screen displays a distorted image or abnormal colors. This is often a problem with the liquid crystal display (LCD) or could be caused by issues with the connecting cables.

The touch screen displays a communication error, and the response to touch is very slow. This issue is not with the touch screen itself but rather with the connection between the Programmable Logic Controller (PLC) or other devices and the touch screen. In many cases, the problem lies with the connecting cables or plugs.

Posted on by — Leave a comment

Global Servo CNC maintenance center

Global Servo CNC maintenance center,Professional maintenance of servo CNC systems

Remember to contact Longi Electromechanical for any issues with servo and CNC systems!

Servo systems differ from VFDs in that they offer higher precision and typically come with delicate encoders. Servo motors are synchronous motors with magnets inside, and if not handled carefully during disassembly and assembly, their original performance may not be restored. Additionally, different servo drivers cannot be used interchangeably with other servo motors. This means that during the repair of a servo driver, a corresponding servo motor and cable plug are required for proper testing. Similarly, repairing a servo motor also requires a matching servo driver for testing, which can pose challenges for many maintenance personnel.

As for CNC (Computer Numerical Control) systems, most are embedded industrial computer types with closed control systems. Each manufacturer has its own design ideas, programming methods, wiring, and communication architectures, making them incompatible with one another.

Longi Electromechanical Company has designed various styles of servo and CNC maintenance test benches to test the working conditions of different CNC systems, servo drivers, or servo motors. When servo systems encounter issues such as no display, phase loss, overvoltage, undervoltage, overcurrent, grounding, overload, module explosion, magnet loss, parameter errors, encoder failures, communication alarms, etc., the corresponding platform can be used to test and diagnose the problem.

Repair Hotline: +8618028667265 Mr. Guo

After resolving these issues, the servo system also needs to undergo a simulated load test to avoid problems such as overcurrent under load conditions, even if it performs well under no-load conditions. This ensures that the servo system is fully functional and ready for use in actual applications.

For the CNC system, it is also necessary to conduct simulated operation before normal delivery to avoid any discrepancy with the on-site parameters. Currently, Rongji Electromechanical possesses hundreds of servo and CNC test benches, which can quickly identify problem areas and promptly resolve issues. With these advanced testing facilities, Longi Electromechanical ensures the smooth operation and reliability of the repaired equipment.

The Servo and CNC Repair Center established by Longi Company currently has over 20 skilled and experienced maintenance engineers who specialize in providing repair services for different brands and specifications of servo and CNC systems. They implement tailored repair solutions for different maintenance projects, ensuring efficient and high-quality service for customers. By helping customers save valuable production time and reducing their maintenance costs, Rongji truly cares about the urgent needs of its customers and strives for common development and progress together.

We have repaired the following brands of servo and CNC systems:

Servo Systems

  • Lenze Servo Systems
  • Siemens Servo Systems
  • Panasonic Servo Systems
  • Eurotherm Servo Systems
  • Yaskawa Servo Systems
  • Fuji Servo Systems
  • Delta Servo Systems
  • Omron Servo Systems
  • Fanuc Servo Systems
  • Moog Servo Systems
  • TECO Servo Systems
  • Norgren Servo Systems
  • SSB Servo Drive Systems
  • Hitachi Servo Systems
  • Toshiba Servo Systems
  • Denso Servo Systems
  • Parvex Servo Systems

CNC Systems

  • Mitsubishi Servo Systems
  • Sanyo Servo Systems
  • Mitsubishi CNC (MITSUBISHI)
  • Fanuc CNC (FANUC)
  • Siemens CNC (SIEMENS)
  • Brother CNC (BROTHER)
  • Mazak CNC (MAZAK)
  • GSK (Guangzhou Numerical Control)
  • Huazhong Numerical Control
  • Fagor CNC
  • Heidenhain
  • Haas CNC
  • NUM (France)
  • Hurco (USA)
  • KND (Beijing KND Technology Co., Ltd.)
  • Leadshine
  • Syntec
  • Shenyang Machine Tool i5
    *凯恩帝 (KND)

Note: Some of the brand names mentioned may be trademarks or registered trademarks of their respective owners. The listing here is for informational purposes only and does not imply any affiliation or endorsement by Rongji Electromechanical or any of the mentioned brands.

Machine Tool Brands

(1) European and American Machine Tools:

  • Gildemeister
  • Cincinnati
  • Fidia
  • Hardinge
  • Micron
  • Giddings
  • Fadal
  • Hermle
  • Pittler
  • Gleason
  • Thyssen Group
  • Mandelli
  • Sachman
  • Bridgeport
  • Hueller-Hille
  • Starrag
  • Heckert
  • Emag
  • Milltronics
  • Hass
  • Strojimport
  • Spinner
  • Parpas

(2) Japanese and Korean Machine Tools:

  • Makino
  • Mazak
  • Okuma
  • Nigata
  • SNK
  • Koyo Machinery Industry
  • Hyundai Heavy Industries
  • Daewoo Machine Tool
  • Mori Seiki
  • Mectron

(3) Taiwanese and Hong Kong Machine Tools:

  • Hardford
  • Yang Iron Machine Tool
  • Leadwell
  • Taichung Precision Machinery
  • Dick Lyons
  • Feeler
  • Chen Ho Iron Works
  • Chi Fa Machinery
  • Hunghsin Precision Machinery
  • Johnford
  • Kaofong Industrial
  • Tong-Tai Machinery
  • OUMA Technology
  • Yeongchin Machinery Industry
  • AWEA
  • Kaoming Precision Machinery
  • Jiate Machinery
  • Leeport (Hong Kong)
  • Protechnic (Hong Kong)

(4) Chinese Mainland Machine Tools:

  • Guilin Machine Tool
  • Yunnan Machine Tool
  • Beijing No.2 Machine Tool Plant
  • Beijing No.3 Machine Tool Plant
  • Tianjin No.1 Machine Tool Plant
  • Shenyang No.1 Machine Tool Plant
  • Jinan No.1 Machine Tool Plant
  • Qinghai No.1 Machine Tool Plant
  • Changzhou Machine Tool Factory
  • Zongheng International (formerly Nantong Machine Tool)
  • Dahe Machine Tool Plant
  • Baoji Machine Tool Plant
  • Guilin No.2 Machine Tool Plant
  • Wanjia Machine Tool Co., Ltd.
  • Tianjin Delian Machine Tool Service Co., Ltd.

Note: The list provided above is comprehensive but not exhaustive. Machine tool brands and manufacturers are constantly evolving, and new players may have emerged since the compilation of this list. Always refer to the latest industry updates for the most accurate information.

Posted on by — Leave a comment

Global Variable Frequency Drive (VFD) repair center

“Longi Electromechanical” has more than 20 years of experience in industrial control maintenance, and is one of the earliest companies engaged in VFD repair. Equipped with artificial intelligence AI maintenance instruments, it specializes in emergency repair of various equipment, with high technical efficiency. It has repaired more than 200,000 units of equipment, including ultrasonic, robot, charging pile, inverter,Variable Frequency Drive (VFD), touch screen, servo, intelligent instrument, industrial control machine, PLC and other products. General problems can be repaired on the same day. LONGI promises you that “if it can’t be repaired, we won’t charge you”. And it provides lifelong maintenance service and free technical consultation for inspection! For urgent repair consultation, please call the contact number or add WHATSAPP maintenance hotline: +8618028667265 Mr. Guo

From European and American brands to Japanese, Korean, and Taiwanese ones, until various domestic brands, we have repaired countless models and specifications of VFDs. In the process of serving our customers, we have continuously learned and accumulated maintenance experience to enhance our skills. We specialize not only in repairing VFDs but also in summarizing various maintenance experiences, elevating them to a theoretical level. We have published the book “VFD Maintenance Technology” and offered VFD maintenance training, thereby promoting the development of the VFD maintenance industry. Longi Electromechanical Company has repaired VFDs from the following brands:

European and American Brands

ABB drives, SEW drives, LUST VFD, LENZE VSD, Schneider drives, CT drives, KEB VSD, Siemens drives, Eurotherm VFD, G.E. VFD, VACON VSD, Danfoss VFD, SIEI VFD, AB VFD, Emerson VFD, ROBICON VFD, Ansaldo VFD, Bosch Rexroth VSD, etc.

Japanese Brands:

Fuji INVERTER, Mitsubishi INVERTER, Yaskawa INVERTER, Omron INVERTER, Panasonic INVERTER, Toshiba INVERTER, Sumner INVERTER, Tooka INVERTER, Higashikawa INVERTER, Sanken INVERTER, Kasia INVERTER, Toyo INVERTER, Hitachi INVERTER, Meidensha INVERTER, etc.

Taiwanese Brands:

Oulin INVERTER, Delta INVERTER, Taian INVERTER, Teco INVERTER, Powtran INVERTER, Dongling INVERTER, Lijia INVERTER, Ningmao INVERTER, Sanji INVERTER, Hongquan INVERTER, Dongli INVERTER, Kaichi INVERTER, Shenghua INVERTER, Adlee INVERTER, Shihlin INVERTER, Teco INVERTER, Sanchuan INVERTER, Dongweiting INVERTER, Fuhua INVERTER, Taian INVERTER (note: Taian is repeated, possibly a mistake in the original list), Longxing INVERTER, Jiudesongyi INVERTER, Tend INVERTER, Chuangjie INVERTER, etc.

Chinese Mainland brands:

Senlan Inverter, Jialing Inverter, Yineng Inverter, Hailipu Inverter, Haili Inverter, Lebang Inverter, Xinnuo Inverter, Kemron Inverter, Alpha Inverter, Rifeng Inverter, Shidai Inverter, Bost Inverter, Gaobang Inverter, Kaituo Inverter, Sinus Inverter, Sepaxin Inverter, Huifeng Inverter, Saipu Inverter, Weier Inverter, Huawei Inverter, Ansheng Inverter, Anbangxin Inverter, Jiaxin Inverter, Ripu Inverter, Chint Inverter, Delixi Inverter, Sifang Inverter, Geli Te Inverter, Kangwo Inverter, Jina Inverter, Richuan Inverter, Weikeda Inverter, Oura Inverter, Sanjing Inverter, Jintian Inverter, Xilin Inverter, Delixi Inverter, Yingweiteng Inverter, Chunri Inverter, Xinjie, Kemron-Bong Inverter, Nihonye Inverter, Edison Inverter

Other brands:
Migao VFD, Rongqi VFD, Kaiqi VFD, Shiyunjie VFD, Huichuan VFD, Yuzhang VFD, Tianchong VFD, Rongshang Tongda VFD, LG VFD, Hyundai VFD, Daewoo VFD, Samsung VFD, etc.

Longi Electromechanical Company specializes in the maintenance of VFDs and strictly requires its engineers to followlow standard operating procedures. Upon receiving a unit, the engineers carefully inspect its exterior and clarify any fault conditions with the customer before beginning work. Any removed circuit boards are cleaned using ultrasonic cleaning equipment. Repaired circuit boards are coated with high-temperature and high-pressure-resistant insulating paint, dried in a drying machine, and then reinstalled in the VFD, with measures taken to prevent corrosion and interference.

The repaired VFD will undergo a simulated operation with load using a heavy-load test bench to avoid any potential issues that may arise under actual load conditions on site.

When it comes to VFD maintenance, most cases are related to the equipment on site. Sometimes a standalone unit may have been repaired, but it doesn’t work properly when installed on site. In some cases, the problem lies with the system rather than the VFD itself. For such issues, if the customer requests on-site service, we will do our utmost to resolve the problem for them. If the location is far away, such as in another province, we can use tools like video conferencing and phone calls to allow our engineers to remotely diagnose and resolve the on-site issues for the customer.