The Siemens 6SE70 series inverter's operation control panel PMU LCD display is not working, showing a "black screen."
(1) Fault Phenomenon: The Siemens 6SE7021-1TA61-Z inverter's PMU LCD display is completely black. After checking the bottom board, the gate protection chip resistor (24Ω) was found to have changed from its normal value of 500kΩ to 500kΩ, indicating damage. The voltage at pin 20 of the N2 integrated block was zero, while pin 1 showed 11.3V. For the N3 integrated block (MC340), pin 4 had 4V and pin 2 had 3.3V. Removing the N3 block with a hot air gun, the resistance between pin 1 and pin 3 was measured at 9kΩ, which should normally be 500kΩ. Replacing the N3 block and the 24Ω SMD resistor resolved the issue. Testing confirmed that the N2 and N3 blocks were operating correctly. The main power supply for the PMU LCD failure was traced back to the V34 power control electrode’s 24Ω protection resistor, which had changed values, typically ranging from 500kΩ to 1MΩ. Some resistors had become open circuits.
(2) Fault Phenomenon: The PMU LCD is still black. Checking the bottom board, the K4 relay coil's parallel freewheeling diode V20 and the series diode V16 were found to be shorted. The N7 power block L7824 was damaged, and the resistance at pin 4 of the N4 UC3844AN was measured at 500Ω instead of the normal 15kΩ. Replacing the diodes, N4, and N7 blocks restored normal voltages. The system now operates properly.
(3) Fault Phenomenon: The PMU LCD is black again. Upon inspection, the 7.5kΩ resistor between pins 4–8 of the N4 UC3844AN was burned out. The R133 gate current-limiting resistor of V34 FET K2225 had increased to 720kΩ. Replacing these components and restoring wiring resulted in normal operation.
(4) Fault Phenomenon: The PMU LCD remains black. On the bottom board, the V34 FET K2225 gate protection resistor (24Ω) was found to be 430kΩ. Between the secondary winding of the power transformer T6, the V58 diode in series with a 100Ω resistor had one resistor changed to 10MΩ and another to 1MΩ. Replacing the 24Ω and 100Ω resistors fixed the problem.
(5) Fault Phenomenon: The PMU LCD is still black. The fuses F1 and F2 (25A) were blown. Measuring the IGBT module output between U and V phases showed a short circuit (11Ω instead of 210kΩ). The trigger board A12, A32, A22 also showed shorted resistances. Replacing the IGBT module (BSM15G120DN12) and the trigger board restored normal function.
(6) Fault Phenomenon: The PMU LCD is black. Checking the backplane, the N4 (UC3844) PWM block had an external oscillation resistor that changed from 7.5kΩ to 420kΩ. Replacing it allowed the system to operate normally.
(7) Fault Phenomenon: The PMU LCD is black. The gate current-limiting resistors R133 (100Ω and 24Ω) on V34 (K2225) were burned out. The overcurrent protection resistor on the N4 (UC3844) had changed from 100Ω to 400kΩ. Replacing these components restored normal operation.
(8) Fault Phenomenon: The PMU LCD is black. In the switching power supply, the oscillation resistor at N4 (4th and 8th pins) had increased from 7.5kΩ to 420kΩ. The output resistor R133 had gone from 100Ω to 300Ω. The voltage detection part N1 (TL084) had a resistor R203 change from 47Ω to 544kΩ. Several resistors on the trigger board also showed abnormal values. Replacing all affected components restored full functionality.
(9) Fault Phenomenon: The PMU LCD is black. The V34 (K2255) FET gate current-limiting resistor (2000Ω) was burned out. The base resistors of V28 (5C) triode (10kΩ and 1.2kΩ) were also burned. The MC340 reference voltage block’s first pin resistor (1000Ω) was damaged. Replacing these components brought the system back to normal.
(10) Fault Phenomenon: The PMU LCD is black. Checking the backplane, V34 (K2255) and drain resistor R400 (10Ω) were burned out. Replacing them and plugging in the CUVC board allowed the inverter to boot up with “008†code, re-initialize, and run after parameter input.
(11) Fault Phenomenon: The PMU LCD is black. During power-up, the switching power supply made a loud "buzz" sound. Measuring the N2 integrated block output, the 20-pin voltage was slightly low at 14.95V instead of 15.30V. The current detection board A1 had a resistance between 4–7 pins of 2.84Ω instead of 3.1kΩ. Replacing A1 caused a "F029" error, which was resolved by replacing the current transducer T4. After this, the inverter operated normally.
(12) Fault Phenomenon: The PMU LCD is black. After self-test, relay K3 activated and then released, causing X9 7–9 pins to close and immediately open. The output voltages were normal, but the current detection board A1 had a resistance between 4–6 pins of 2140Ω instead of 3200Ω. Replacing A1 restored normal operation.
(13) Fault Phenomenon: The PMU LCD is black. The secondary power supply showed the V2 (IRF520) FET gate current-limiting resistor had changed from 10Ω to 590kΩ, and later to 11MΩ. Replacing it restored normal operation.
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