Tag: INVERTER REPAIR

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What should be done if the CONVO VSD is not connected to the motor and the frequency of the motor cannot be adjusted?

A 5.5kW Konwo frequency converter sent for repair, the customer said: there is output, but it cannot operate with load, the motor cannot rotate, and the operating frequency cannot be adjusted. Check the main circuit, rectifier and inverter circuits, all of which are normal. Power on, measure the three-phase output voltage without load and it is normal. Connect a 1.1kW no-load motor and start the frequency converter to run. The frequency cannot rise near one or two hertz, and the motor has a pause and produces a creaking sound. No overload or OC fault is reported. Stop and restart, still the same.
Disconnect the 550V DC power supply of the inverter module and send another 24V DC low-voltage power supply to check the driving circuit. Check the capacitors and other components of the driving circuit and driving power supply circuit, and they are all normal. The positive and negative pulse currents output by the three arm drive circuit on the inverter output have reached a certain amplitude, and there should be no problem driving the IGBT module; But when measuring the positive and negative pulse currents output by the three arm drive circuit, a module fault is reported. Analyze the reason, as the DC current range of the multimeter is directly short circuited to measure the triggering terminal, the internal resistance of the DC current range of the multimeter is small, which greatly lowers the positive excitation voltage output by the driving circuit, such as below 10V. This voltage cannot trigger the IGBT tube normally and reliably. Therefore, the module fault detection circuit detects the voltage drop of the IGBT tube and reports a fault in the OC module. The fault was actually caused by the measurement method. When the probe was connected in series with a resistance of more than ten ohms and the output current of the drive circuit was measured, the OC fault was not reported. Check the signal output circuit of the current transformer again, and it is also normal. During operation, no fault signal is reported.

I feel like there’s nowhere else to go and I can’t find the cause of the malfunction. Is the problem with the driver, module, current detection, or other circuits? The fault was not detected throughout the afternoon. For a moment, I felt a bit indifferent and worried.

  1. Does the CPU detect abnormal current during startup and take measures to slow down?
  2. Is the current limiting action made by the driving circuit due to abnormal driving or poor module performance?
    Under low-frequency operation, try to short-circuit the shunt resistors of the U, V, and W output circuits to make the CPU exit the frequency reduction and current limiting action, which is ineffective;
    Restoring the parameters to their factory values (suspecting that this operating mode may have been manually set) is invalid.
    Start the frequency converter and observe carefully: after the speed rises to 3Hz, it drops to 0Hz, and repeat this process. The motor stops running.
    After significantly increasing the acceleration time, it steadily increased to 3Hz and then decreased to 0Hz, indicating that there were no abnormalities in the driving and other circuits. This operating phenomenon should be formed based on the signal emitted by the CPU, which seems to act as a current limiting action based on the current signal.
    The self deceleration during the starting process is generally due to the following two reasons:
  1. During the startup process, the CPU detects a sharp increase in abnormal current values and performs immediate frequency reduction processing. When the current returns to within normal values, it then increases the frequency for operation;
  2. During the startup process, the CPU detects an abnormal drop in the DC voltage of the main circuit and performs immediate frequency reduction processing. When the voltage of the main circuit returns to within normal values, it then increases the frequency for operation;
    After the drive and current detection circuits have no issues, maintenance should be carried out from the perspective of voltage.
    The anomalies caused by voltage can also be divided into two aspects:
  3. Caused by abnormal DC voltage detection circuit in the circuit (drift of reference voltage, variation of sampling resistance, etc.). This signal causes the CPU to mistakenly assume that the voltage is too low, and therefore takes measures to reduce the output frequency to maintain a stable voltage;
  4. The abnormality of the main DC circuit causes a low voltage (loss of capacity of the energy storage capacitor, failure to close the charging short circuit contactor, etc.), which is detected by the detection circuit and causes the CPU to take a frequency reduction action during the startup process.
    Reinstall and power on the machine, and conduct a motor test. When powered on, no sound of the charging contactor closing was heard. Check that the contactor coil is AC 380V, taken from the R and S power supply incoming terminals. Loose coil lead terminals caused poor contact, and the contactor failed to engage. The large current during startup creates a significant voltage drop on the charging resistor. The sharp drop in the DC voltage of the main circuit is detected by the voltage detection circuit, prompting the CPU to issue a frequency reduction command.

The reason for taking many detours is that the machine only performed frequency reduction treatment when the voltage dropped, and did not report an undervoltage fault. In this case, other models often have reported undervoltage faults. Also due to the reason of no load, during frequency reduction processing, the voltage quickly rises and the frequency continues to rise. Then the voltage drops again, and the frequency converter reduces the frequency processing, allowing the voltage to rise again. This repeated process causes the frequency converter to increase speed, decrease to zero speed, pause and then increase speed again, and then decrease to zero speed. But it does not shut down and does not report any fault signals.
It’s a bit funny that such a simple fault should be thoroughly investigated on its normal circuit. Due to its failure to report fault codes, the inspection steps were somewhat bewildered.
This article is shared with everyone – when the charging contactor of the Kangwo inverter is in poor contact, it may be adjusted in a frequency reduction manner during the starting process in a light load state, without reporting an undervoltage fault signal and implementing shutdown protection. In the loaded starting state, the DC circuit should have a significant drop and should be able to report an undervoltage fault.
The frequency converter is an organic combination of software and hardware circuits, and the above fault phenomena are formed under the automatic control of software programs. If we only rely on the fixed thinking pattern formed by surface phenomena and past experience, without in-depth analysis and detailed observation, we would really treat this simple fault as a difficult one to repair.

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Maintenance and Fault Shielding Tips for the Drive Circuit of Senlan Inverter sb40-s11-11kw

Repair a Senlan SB40-s11-11kw frequency converter. Upon inspection, it was found that the output terminals u and p+of the module were damaged due to breakdown. As usual, after removing the damaged module, power on the circuit board separately to check if the drive circuit is abnormal. Power on and trip the ole fault. According to the manual, it is an external alarm signal. After short circuiting the control terminal Thr to cm, the power on display is normal. However, when the run button is pressed, a fl fault code will jump, indicating module failure. The drive board is a relatively large circuit board, There are over twenty integrated blocks on top, right? I don’t know why it’s so complicated. Observing the six optocouplers on the back, it should be returning a fl fault to the CPU. Check that the outputs of the six optocouplers are parallel. So short circuit all the input sides, power on, and start running. Sure enough, there is no fl fault code jumping. But when measuring the voltage on the trigger terminal of the module, I was dumbfounded: why is there no voltage! Take a closer look at the driving power supply of the three arm IGBT tubes on u, v, and w, which is output by the switching power supply on the motherboard at 12V, then oscillated and inverted by NE555. Then, a cylindrical sealed transformer is used to extract the voltage from the secondary three windings and rectify it to form three independent driving power supplies. Measure that all three power supplies are available. Then observe that the three driving signals are output by two pairs of tube push pull, which drives the module, The power supply added to the push-pull tube is also available. However, there is no voltage on the trigger terminal of the module, which not only does not have the conventional static negative pressure, but also does not have the excitation positive voltage during operation. Where did this trigger voltage go? Is it possible that the damage to the module was caused by the loss of this voltage? Is it due to a common problem that all six channels have no voltage? Where can I find this large circuit? And users from other places are in a hurry to use the machine and require it to be repaired immediately! I don’t have time to survey the circuit.

Suddenly, it occurred to me that this large circuit, in addition to processing the six pulse signals sent from the CPU, was probably implementing protection for the module. Six optocouplers were short circuited to return the FL signals to the CPU. Although the CPU believed that the module was no longer faulty and sent the six pulses normally, the large protection circuit on the input side of the optocoupler detected an abnormally large “IGBT conduction voltage drop” during the arrival of the six pulses due to the removal of the module, And it was determined that the module was damaged. While sending this fault signal back to the CPU through the six optocouplers, a protective action was also taken. The signal on the module trigger terminal was cut off! It is necessary to artificially create a false image of IGBT tube conduction, deceive the conscientious protection circuit, and release its protection state, in order to check whether the driving circuit can output six qualified excitation pulses, and then determine whether a new module can be replaced for repair
How clever, clever, quick witted! Following this approach, (as the circuit board is powered on separately, the voltage of the 550V DC circuit introduced by p+and n – has been disconnected from the driving circuit. In fact, the purpose of introducing these two terminals into the driving circuit is to form a triggering circuit for the u, v, and w lower three arm IGBT tubes, and to detect the voltage drop of the six IGBT tubes during conduction. In case of abnormalities, the circuit will be protected to protect the safety of the module.) Connect the upper three channels of the triggering terminal with the three terminals that are directly connected to u, v, and w, Connect the n-point, which means that the tubes of the lower three arms were artificially short circuited. At the same time, the short circuiting of the corresponding three optocouplers (those reporting fl faults) was released. After powering on, and starting operation, the fl fault was indeed no longer reported. The triggering terminal of the lower three arms of the measurement module had a positive pulse voltage output. The DC voltage was 4V and the AC voltage was 15V, normal! Follow this procedure again, connect the upper three circuits of the trigger terminal with the three terminals that are directly connected to u, v, and w, and connect them to point p+. That is, artificially short circuit the pipes of the upper three arms. After powering on, start the operation, and measure the trigger terminals of the upper three arms of the module, which also have normal pulse voltage output. This indicates that the entire drive circuit and operation control are normal, and the module can be replaced and repaired

The frequency converter has no cut-off negative pressure. In the shutdown state, the triggering terminal voltage is zero
After replacing the module, the machine is repaired
Ideas determine the way out

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Circuit diagram and maintenance skills of CONVO VSD switch power supply

This is the circuit diagram of the switch power supply for the GVF-G type of the CONVO drivers, with a power of 5.5KW and version number 002-E-P00-01 8.6kVA 13A. This circuit is not considered a very classic switch power supply circuit, but it does not mean that it is a poorly performing circuit, and its failure rate is not high in actual operation.

The input of the circuit is approximately 550V DC voltage at both ends of the autonomous DC home energy storage capacitor. The oscillation and driving are carried out using commonly used power chips 38440, which provide the circuit’s starting voltage and current from R40, R41, and Z8. The Z8 voltage stabilization value has not been measured yet, and is estimated to be around 13V. Here, the LED also serves as a power indicator. After the vibration of 3844, the 7-pin power supply voltage of 3844 is established through rectification and filtering circuits such as D13, Dl4, C30, and C31 through the BT winding. At the same time, this power supply also undertakes the functions of output voltage sampling and voltage feedback. After being divided by R1 and R2, it is sent to the 2 pins of 3844 for feedback voltage input. This is different from the voltage feedback method of switch power supply circuits in other brands of frequency converters. Due to the fact that voltage sampling is not directly taken from the secondary power supply branch of the transformer, it can only be considered as an indirect sampling of the output voltage of each channel, so the control strain rate and accuracy are not too high. However, the+18V and -18V power supply of the secondary winding were introduced into the CPU motherboard, and voltage stabilizing links of 7815 and 7915 were added respectively. The circuit was slightly cumbersome, and its power supply performance was correspondingly improved. After the+8V power supply was introduced into the motherboard, 7805 voltage stabilization processing was added as the power supply for the CPU.
The sampling of the switching tube current is obtained from the resistor R37 connected in series with the K2225 source of the switching tube as usual. Sent to the 3-pin current detection terminal of 3844. 1. The feedback component of the internal voltage amplifier is connected between the two pins, which determines the amplification rate of the sampling voltage. The 8-pin is the Vref terminal, which outputs a 5V reference voltage during normal operation, providing a current path for the external R and C oscillation timing components of the 4-pin, ensuring the stability of the oscillation frequency. The 6 pins are pulse output pins, also known as drive output terminals. Introduced into the gate of switch K2225 through R36.
The 24V output power supply not only provides 24V control voltage for the frequency converter control terminal, but also supplies power to two cooling fans. It can be seen that the operating mode of this fan is controlled by the CPU motherboard signal and determined by parameter settings. There are generally three operating modes: running after power on, running during operation, and running when the radiator temperature reaches a certain value.
Maintenance tips: When the switch tube K2225 is damaged due to breakdown, a high voltage impulse is introduced from pin 3 of 3844, which often causes damage to the R5 resistor. The resistor may also have opened or increased in value:

Maintenance tips: When the switch tube k2225 is damaged due to breakdown, 3844 is often damaged simultaneously due to the introduction of high voltage surge from three pins; The r5 resistor may also be open or the resistance value may have increased; Most of the current sampling resistors r37 connected to the source have also been opened. Before replacing the switch tube, it is necessary to conduct a comprehensive inspection. The switch tube k2225 can be directly replaced with k1317 tube.

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Repair process of OC alarm for PI-18 type 11kW POWTRAN VFD drive

Repairing a PI-18 type 11kW universal frequency converter, many “secrets” were discovered during the processing. The summary is as follows: 1. The damage to the module is not only a short circuit or open circuit in the main current terminals R, S, T and U, V, W, but also possible short circuits between the triggering terminals and the main terminals, short circuits between the triggering terminals, and open circuits inside the triggering terminals. Measuring that there is no short circuit in the main terminal does not confirm that the module is not damaged; 3. Assuming that there are no issues with the measurement of the main terminal and trigger terminal, it cannot be completely confirmed that the module is not damaged. There are still hidden damages such as leakage and poor performance in the module. The key is to take measures to verify its quality and ensure that the final installed block is a good one. And during the power on debugging process, it will not cause new faults, thereby expanding the scope of faults and causing human trouble. Special attention should be paid to the selection of disassembled modules. There is no abnormality measured with a multimeter, but there may be potential damage. Choose a good module, and the DC voltage of the main circuit should not be easily delivered. It is necessary to first use a lower DC power supply and verify that there are no abnormalities before connecting the DC bus circuit and conducting a startup test.

A. Abnormalities encountered during repair:
Measure the terminals of the main circuit for any abnormal phenomena such as short circuits, and especially test the other pins of the inverter module once to confirm that they can be powered on for testing; Power on, display normal, press the start button when unloaded, trip OC protection and stop.
To verify the source of this overcurrent signal, check the input processing circuit of the current transformer, which is LM347 (with the same structure as LM324). If the input and output states are manually changed, the frequency converter does not respond. It appears that the OC signal is not output by the current detection circuit.
Considering that it is still fed back by the inverter module, a thorough inspection of the driving circuit, including the filtering capacitors of the four power sources in the circuit, and a capacity check have also been conducted. No abnormalities.
The driving circuit of this machine adopts three integrated circuits, namely A4504, MC33153, and P521. A4504 is the isolation optocoupler between the CPU input trigger pulse and the main circuit, MC33153 is the module driver, and P521 is used to feedback abnormal conditions of the inverter module to the CPU, in order to achieve rapid shutdown protection. During power on, whether in standby or startup mode, short circuit any output terminal of the six P521 circuits, and the frequency converter will trip OC protection to stop the machine. The circuit is very sensitive. The start under no-load conditions triggers the OC, which is mostly fed back to the CPU by these six optocouplers.
It was determined that the inverter output module SKM75GD124D was damaged. After the power outage, a multimeter was used to carefully check and no abnormalities were found. The measurement results of the six main terminals and other trigger terminals are the same when compared with a good block. Give it a try by changing it. Only the replacement module has been tested.
Purchase a dismantling product of the same model, disconnect the DC power supply of the module after welding, activate the operation panel button, and the panel displays normal frequency output. Measure the DC voltage of the six drive outputs -0V when the module trigger end is not started and running, and around 7.6V after starting, all of which are normal. Using an oscilloscope to measure the amplitude and variation of the six trigger pulses is also normal, and it is determined that the driving circuit and connecting wires are accurate and error free.
I still didn’t dare to rashly connect to the DC bus. I first connected the DC24V switching power supply and tried to start it. The frequency display of the frequency converter was normal, and the output voltage of U, V, and W was measured. At 50 Hz, the voltage was only 13V, and there was a periodic contraction in the output amplitude, but it could still be triggered and operated normally. Due to unfamiliarity with the output waveform, this phenomenon was not noticed, and a DC power supply of around 200V was connected. When powered on, the OC still jumped! I feel like there is still a problem with the module! Replace with a confirmed good module on the ground, connect to a 24V switching power supply, and then measure the output voltage of U, V, and W. At 50Hz, the voltage value has risen to 17.8V, and the output amplitude is constant without any contraction phenomenon. This is the good block!
The internal IGBT tube of the purchased disassembled module was not directly broken down, but it was damaged and had a large leakage current. When connected to a 24V power supply, although the output dropped to 13V, it did not cause a fault protection action. However, when connected to a DC power supply above 200V, the leakage current had reached a certain value, leading to fault action.
I purchased another disassembled product and after repeating the above steps, everything was confirmed to be normal before proceeding with installation. Finally fixed.
Disassembling the machine module is not unusable, but it must be used with caution. Due to the extremely difficult process of soldering the module onto the circuit board and removing it, it is best to connect a lower DC power supply before installation and check its quality. If the block is damaged, clean the solder on the pins and it can be returned or replaced. After confirming the good block, solder it into the circuit board.

B. Reiterate the repair steps:

  1. All six phase output trigger pulses are normal, and the inverter module can be soldered;
  2. First, use a 24V switching power supply to conduct a power on test, and if there are no abnormalities, then send the DC bus voltage (such as abnormal driving circuits and leads, adding a 24V switching power supply will not damage the module. Pay attention to measuring whether the three-phase AC output is balanced and whether there is DC component in the output. If there is an abnormality, there is often a lack of trigger pulse in one arm or abnormal trigger pulse. The detection in this stage is crucial, and the hidden dangers of faults are often exposed);
  3. Connect the DC power supply circuit in series with the light bulb, then connect the inverter module, conduct no-load power transmission test, measure the three-phase balance of the output, and finally connect the original DC power supply. During this process, if there are any potential faults in the module, it will be further exposed.
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Repair process of TECO 7200GA-22kW VSD after lightning strike

Received a 7200GA-41kVA frequency converter for repair, which is a lightning fault. After replacing the damaged input rectifier module, switch tube, and shunt tube of the switching power supply, the operation panel screen displayed normally, indicating that the problem is not significant.

The negative pressure and optocoupler drive input signals of the six channels were tested to be “normal”. During the assembly test of the whole machine, the OC jumped immediately upon power on, but the operation could be started after resetting. The screen frequency output was normal, but there was no three-phase voltage output at the U, V, and W terminals during the actual test. The local driving IC adopts optocouplers PC923 and PC929, which cooperate with SN0357 to return OC signals.
Check the power amplifier circuit on the output side of the driving IC and the detection circuit of the IGBT tube, and there are no abnormalities. When testing the pulse input pin of PC923, it doesn’t feel right. Why is the level of pin 3 high and pin 2 low? Is it because the driver power supply is reversed? 2. Three pins are the input circuit of the photodiode, two pins are the anode of the photodiode, and three pins are the cathode of the photodiode. According to common sense, the two pins are usually powered by+5V and then stabilized to provide an excitation power of about 4V, while the three pins are connected to the pulse output terminal of the CPU. Low level output is effective, that is, when outputting, current is pulled in from the three pins of PC923 to make the diode conductive. When there is a trigger pulse input and the frequency is low, the voltage of pin 3 oscillates up and down to 3V. As the frequency increases, the voltage of pin 3 gradually stabilizes at around 3V. When there is no output, pin 3 is a high level of around 4V (equal to the level value of pin 2).
The current detection results are as follows: when no running command is input, pin 3 is a high level of 0.5V, and pin 2 is a low level close to 0V; When entering the run command, pin 3 drops to 0.2V and there is a change in high and low levels, indicating that the CPU pulse has reached PC923. At the beginning of the maintenance, I took a detour and only paid attention to the changes in high and low levels, without paying attention to the magnitude of the voltage value. Obviously, the loss of 2-pin power supply voltage prevents the IGBT transistor from receiving excitation pulses, resulting in no output voltage from the frequency converter.
Check that the 2-pin power supply is a simple series connected voltage regulator with a transistor and a voltage regulator. The base bias resistance of the transistor is open, causing the supply voltage to be zero. After replacing the bias resistor, measure the voltage on pins 2 and 3 of PC923 to return to normal. After receiving the operation command, the frequency converter has output from the U, V, and W terminals.
Further investigate the reason for the OC jump upon power on. Measure the SN0357 optocoupler device that transmits the OC signal, and the voltage value of the two pins on the input side is zero, indicating that it did not input the OC signal. However, measure the voltage value of the two pins on the output side of the three optocouplers to be 0.5V! But since there is no OC signal input, the voltage between the two pins should be 5V (one pin is connected to a 5V ground level), and there is only one possibility, that is, the 5V pull-up resistance of the signal output pin has changed or is open circuit. At this point, the CPU mistakenly believes that it has received the OC signal returned by the drive circuit, and therefore gives an alarm. Try connecting a 10k resistor between the signal output pin and the 5V power supply. Start up and test the signal output pin to be 5V. Repeat the power supply several times and no longer experience OC faults.

The above two faults actually come from one reason: power loss. The input pin of the pulse signal and the output pin of the OC signal are both directly connected to the CPU pin. When the pull-up high level disappears, the CPU pin only has a low level of 0.5V left. This level is not enough to drive the optocoupler to send out the trigger signal of the inverter module, and it also leads to the detection of low levels and the jumping of the OC fault code when powered on. And 0.5V is also the critical level for detecting signals such as OC, so after performing a reset operation, it can start running again.
Note:
The motherboards of various series of Dongyuan frequency converters have good replacement characteristics, and after replacement, only the corresponding capacity value of the frequency converter needs to be readjusted. After changing its capacity value, the relevant parameters for checking the rated current value of the motor are also automatically modified.
The capacity labeling of Dongyuan frequency converters is mostly not based on kW, but on kVA. For example, for a 22kW capacity, it is labeled as 41kVA with a rated current of around 48A. In the relevant manual, the capacity is set by comparing the HP horsepower with the rated current. Moreover, the setting of horsepower size is not simply expressed in numerical terms, but also mixed with English letters to indicate the size of horsepower value (actually using hexadecimal notation). When initially adjusting its capacity value, it is often difficult for Master Zhang Er to understand and adjust it, and the parameters cannot be written in.
The corresponding relationship between kW, KVA, and HP values is not clear to most users. I don’t know what the Dongyuan people were thinking about doing this. 1HP=0.75kW, indicating that the horsepower is less than the kW value; KW is the active power value, which can be approximated as the actual power value. That is, a 22kW frequency converter can drive a 22kW motor, and the power capacity is sufficient; And kVA is the apparent power value, which means that when there is such power, but it drives some loads such as motors/inductive loads, it cannot reach the marked output value because the motor load requires reactive power consumption, and kVA is the sum of active power and reactive power. The kVA value is virtual (not discussed here) and can be selected based on the rated current value.

The comparison table between the motor capacity HP and the set value is as follows:
HP: Set value:
25 (18.5kW) 29
30 (22kW) 2A
40 (30kW) 2B
50 (37kW) 2C
60 (45kW) 2D
75 (55kW) 2E
100 (75kW) 2F
125 (90kW) 30
150 (110kW) 31
175 (130kW) 32
215 (160kW) 33

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Repair of Switch Power Supply Fault in TECO 7200GA-30kW Inverter

After being damaged and repaired by lightning strikes, the frequency converter has been running for over a month and has experienced strange malfunctions: there is a random shutdown phenomenon during operation, which may occur every few days or every few hours; Difficulty starting, capacitor charging short circuit contactor jumping during the starting process, starting failed, but the operation panel does not display a fault code. After successfully starting with some effort, it can run for a period of time again.

Remove the control board from the site and short circuit the terminals of the thermal relay to prevent it from entering the thermal protection state and unable to test the machine; Short circuit the contact detection terminal of the capacitor charging contactor to prevent it from entering a low voltage protection state. The machine cannot be tested, and a comprehensive inspection was conducted. No abnormalities were found during the inspection, all of which are good.
Install the control board back into the machine, power on and test the machine. When starting, the contactor jumps and cannot start. After unplugging the connection of the 12CN plug cooling fan, the situation greatly improved and the success rate of starting increased. Upon careful observation, the brightness of the display panel decreased during the startup process, indicating that the fault was due to poor load capacity of the control power supply.
When each power supply output is unloaded, the output voltage is normal. Connect resistive loads to the output of each power source, and slightly reduce the voltage value+ After 24V is connected to the cooling fan and relay load,+5V drops to+4.7V, and the screen display and other operations are normal at this time. But if the frequency converter is put into the startup state, the relay will jump, and occasionally fault codes such as “low DC voltage” and “communication interruption between CPU and operation panel” will appear, causing the operation to fail. In measurement, when+5V drops below+4.5V, the frequency converter will immediately change from starting state to standby state. Detailed inspection of the load circuits of each power supply shows no abnormalities.
Analysis: The judgment of poor load capacity of the control power supply is correct. Due to the strict requirements of the CPU for power supply, it can still barely work at no less than 4.7V; But when it is below 4.5V, it is forced to enter “standby mode”; When the voltage is between 4.7V and 4.5V, a fault alarm will be issued to detect the operation of the circuit.
But unexpectedly, the maintenance of this malfunction was quite tricky, and after checking all the relevant components of the switch power supply, none of them were damaged! Helpless, I attempted to conduct a parallel resistance test on R1 (5101), one of the reference voltage divider resistors of U1 (KA431AZ), with the aim of changing the divider value to increase the output voltage. The measured output voltage has slightly increased, but the load capacity is still poor. Upon closer inspection of the circuit board, it appears that there are welding marks on the diversion adjustment tube Q1, but it appears that its model is the original one. Even if it is replaced, it will still be removed and replaced from similar machines. The switch transistor Q2 of this machine is a bipolar transistor with high back pressure and high amplification, which is difficult to purchase in the market, and the circuit has strict requirements for the parameters of these two transistors. Combined with fault analysis, the working point of the shunt adjustment tube is offset, causing too strong a shunt on the Q2 base current, which will result in poor load capacity of the power supply. Try to connect a resistor R6 (330 ohms) in series with a voltage feedback optocoupler and a 47 ohm resistor to reduce the base current of Q1, thereby reducing its shunt ability towards Q2 and enhancing the load capacity of the power supply. Power on test machine, regardless of loading or starting operation,+5V stable output 5V, troubleshooting!

Fault inference: The Q1 switch tube has aging phenomenon and the amplification ability has decreased. Therefore, the insufficient Ib value after shunt makes it fully conductive (increasing the conduction resistance), resulting in a decrease in the power supply’s carrying capacity; There is a characteristic deviation phenomenon in the shunt branch, which leads to excessive shunt and poor driving of the switching tube, resulting in poor load carrying capacity of the power supply.

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Repair of switch power supply malfunction in Jialing VSD JP6C-9

Power on, there is no display on the operation panel, and the resistance of the input and output terminals of the main circuit is normal. Diagnosed as a power failure on the control board switch. Listening carefully, there are slight intervals of clicking and clicking sounds, which clearly indicate difficulty in starting the power supply. According to experience, this phenomenon is often caused by abnormal power load. Check the rectification, filtering, and load circuits of each power supply, and there are no abnormalities; Disconnect the power supply branches with high current, such as the cooling fan power supply, inverter drive power supply, and operation panel display power supply, but the fault still persists.

Check the peak voltage absorption network in parallel with the primary winding of the switch transformer (connected in series with the diode after parallel connection of the resistor and capacitor). Use a pointer multimeter to measure the forward and reverse resistance of the diode, both of which are 15 ohms, and feel abnormal. Disassemble and test the two parallel diodes, they are normal. Upon closer observation, there are slight cracks in the capacitor. Upon testing its pins, it was found that it was a 2kV 103 capacitor breakdown short circuit. After replacement, the machine returned to normal.
It is rare for this capacitor short circuit to cause switching power supply to have difficulty starting vibration.

The setting of this voltage peak voltage absorption network was originally intended to absorb the abnormal peak voltage generated during the cut-off period of the switching tube, which endangers the safety of the switching tube. However, after capacitor breakdown, the primary winding of the switching transformer is equivalent to parallel connection of diodes. For switch transformers, the energy absorbed during the conduction period of the switch tube is quickly discharged by the diode during the cut-off period of the switch tube, which cannot accumulate oscillation energy. At the same time, the diode acts as an excessive load on the switch transformer, causing difficulties in starting the switch power supply.。

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Maintenance of Switch Power Supply Fault in Taian N2-1013 VSD

Upon powering on, there was an OC fault. It was detected that the inverter output module was not damaged, and most of the six inverter drive ICs were damaged. Further inspection revealed a peculiar phenomenon in the switch mode power supply: when the CPU motherboard was disconnected for power supply,+5V was measured to be normal, but the power supply of other branches was higher than normal, such as+15V being+18V, and the driving power supply of 22V being 26V. When the wiring block of the CPU motherboard was connected,+5V was measured to be normal, but the power supply of other branches showed an abnormal increase! If the driving power supply of 22V even rises to nearly 40V (the maximum supply voltage of PC923 and PC929 is 36V), the damage to the driving IC is caused by this.

Key inspections were conducted on the voltage stabilization process, and peripheral circuits such as IC202 and PC9 showed no abnormalities. Further investigation revealed no abnormalities in other circuits, and maintenance was deadlocked.
Analysis: The voltage stabilizing part of the circuit works. The voltage sampling of the voltage regulator circuit is taken from the+5V circuit. When the wiring block of the CPU motherboard is unplugged, it is equivalent to a light load or no load of+5V. The rising trend of+5V increases the negative feedback of the voltage, reduces the duty cycle of the power switch driver pulse, reduces the excitation current of the switch transformer, and the output voltage of other branches is relatively low; When inserted into the wiring block of the CPU motherboard, it is equivalent to a+5V load or overload. The decreasing trend of+5V reduces the negative voltage feedback, increases the duty cycle of the power switch driver pulse, and increases the excitation current of the switch transformer, causing the output voltage amplitude of other branches to increase. The current situation is that when the+5V circuit is unloaded, although the output of other power supplies is lower, it is still higher+ After 5V loading, other power supply branches exhibit abnormally high voltage output! The faulty link is either due to a malfunction of the power supply itself causing a decrease in load capacity, or an abnormality in the load circuit. Both abnormalities have caused the voltage regulator circuit to undergo conscientious “misregulation”, resulting in the maintenance of the “voltage stability” of the+5V faulty circuit and the occurrence of “abnormal voltage changes” in other power supply branches!

Start repairing the+5V circuit, unplug the power filter capacitor C239220u10V, and check that the capacity is only a dozen microfarads, with obvious leakage resistance. The failure of a capacitor perfectly satisfies two conditions: a decrease in capacity reduces the power supply’s carrying capacity, and leakage causes the load to become heavier.
After replacing this capacitor, the test run was normal.