Tag: VSD maintenance

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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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Handling Method for SC Jumping Fault of GS Series INVT VSD

SC: Refers to a short circuit in the output load of the frequency converter. In the state of power outage, there is no short circuit between U, V, W and between U, V, W and DC P, N. To distinguish whether it is a current detection circuit fault on the CPU motherboard or a signal returned by the driving IC, short circuit the signal to the diode side of the optocoupler device with a wire, and operate the RUN key after power on. The output frequency displayed on the panel is normal. The SC signal is returned by the driving IC, and there are two reasons for the malfunction: first, the inverter module is damaged, and second, the driving IC itself is faulty.

After cutting off the power supply to the inverter module, the six pulse signals of the drive IC were checked again. It was found that the U-upper arm drive IC had input pulses but no output pulses (static negative pressure normal). After replacing the drive IC, the output was normal. The static negative pressure of the U lower arm drive IC is only a few tenths of a volt. After replacement, the fault still persists. After welding the 100 ohm resistor connected to the trigger end of the inverter module, the static negative pressure rises to the normal value. The forward resistance of the lower arm terminal of the module U is consistent with the resistance of other trigger terminals, but its reverse resistance is slightly smaller than that of other trigger terminals, indicating that the circuit inside the U-phase trigger terminal of the module is damaged!
This is a key point in checking module faults: the resistance of the main terminal cannot be roughly measured to be normal, which means that the module is good. It is not uncommon for the circuit inside the triggering terminal to be damaged, but it is more concealed! When the frequency converter reports an SC or OC fault and the main terminal of the detection module is normal, the inspection of the forward and reverse resistance of the triggering terminal should not be missed!
The damage of modules and the damage of driving ICs are usually related: when the U-phase main circuit is damaged, the upper and lower arm driving ICs of the U-phase are often also damaged by strong voltage shocks; When the driver IC of the phase is found to be damaged, it often hides the internal circuit damage of the triggering terminal of the phase. So one of the two is that a comprehensive inspection must be conducted. Of course, there are also cases where modules and driver ICs are damaged separately, but it is extremely rare.

During maintenance, another phenomenon of drive IC failure was also discovered in the low-power model of the Envision GS: when the frequency converter is powered on and there is an SC fault signal output, the CPU performs self check, reset, and reset, and after clearing, the panel only displays H:00, and all panel buttons fail to operate. When the corresponding optocoupler circuit is short circuited to eliminate the SC signal, all panel operations are normal. If the model detects an SC fault signal output when powered on, it may perform a “program lock” and refuse to operate! When this phenomenon occurs, the fault signal output circuit should be checked and corresponding measures should be taken to temporarily eliminate the fault signal, in order to facilitate operation and judgment, and thus solve the fault.

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A Hidden Cause of Alpha Inverter OC Fault Tripping and Shutdown

During the maintenance of the Alpha low-power inverter, it was discovered that the inverter has a common problem – it is prone to OC failure. It manifests as: often jumping faults during start and stop operations, but sometimes also jumping faults during operation; Sometimes it inexplicably improves and can run for varying lengths of time. When I thought there was no problem, I started to frequently skip OC faults again; When measuring the output voltage of U, V, and W with a probe under no load, it is prone to tripping faults. However, after connecting the motor, it starts running and does not jump again. After a while, the OC fault still jumps when connecting the motor.

The handling of such faults is quite tricky, and it is possible that the fault has been eliminated during the testing process, resulting in no evidence for investigation. Even when testing the hardware circuit (protection circuit) during frequent malfunctions, I couldn’t find any problems and couldn’t figure out the root cause of the problem. This problem puzzled me for over two months.
The hardware protection circuit is mainly completed by two LM393 dual operational amplifier circuits, U22 and U24. The signal is then inverted by a first stage inverter and sent to pin 16 of the CPU. U22 and U24 jointly input two output current signals, one overload OC signal returned by the inverter drive IC, and one DC voltage detection signal, which are respectively added to the input terminals of four operational amplifiers. After open-loop amplification processing (the operational amplifier circuit is actually used as a switch circuit here), Four fault signals were connected in parallel, and after undergoing a first level of phase inversion processing, they were sent to pin 16 of the CPU. I first cut off the overload OC signal returned by the inverter drive IC, and then cut off the “total” fault signal of the inverter output, but both were ineffective, and the fault phenomenon still persists. Is there another way to string in OC signals elsewhere? Impossible!
There may be some inexplicable interference in the circuit, but the source and cause of the interference are difficult to identify. We racked our brains and exhausted all means to install capacitor and resistor filtering elements in the fault signal circuit to improve the anti-interference performance of the circuit, but to no avail. Could it be that during the loading and unloading process of the inverter drive module during the start/stop moment, the fluctuation of CPU power supply caused the malfunction? The measured CPU power supply is 4.98V, which is very stable and meets the requirements.
Without any reason, I had a sudden inspiration and adjusted 4.98V to 5.02V. After conducting a start/stop test, the fault was surprisingly eliminated!
Analyze and speculate the cause of the malfunction as follows: the setting of the static voltage working point outside or inside the CPU is improper or too low, which is exactly at the critical point of signal interference level, making it easy to experience random OC faults that are confusing. After slightly increasing its 5V power supply, the voltage value at its operating point also increases accordingly, avoiding the critical point of interference level, and the frequency converter changes from “neural” to “normal”.

When the machine leaves the factory, if the CPU power supply adjustment value is slightly higher, the machine can run normally for a long time. If the adjustment value is slightly lower, or if there is a slight decrease in 5V due to some reason (such as component variation, temperature drift, etc.) during use, frequent OC tripping faults may occur. Adjusting the 5V power supply can easily solve the problem while ensuring that there are no issues with the hardware protection circuit. If it is not due to an accidental factor, then the depth of the concealment of this fault makes it difficult to “adjust” it properly.