Four Cases of Electrical Fault Treatment of KBA Rapida 104 Four-color Offset Press
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Fault 1
When the first color is engaged, there is sometimes no pressure, and the same phenomenon occurs during manual pressing. The piezoelectric solenoid coil was checked, and the resistance value was normal, but at times the 24 V power supply was not present. When X10 of WP12 should have a green indicator light, it does not illuminate. Each time an output indication appears on the output module in the electrical cabinet, there is no voltage output. It is suspected that the micro relay in the output module is damaged.
After interchanging output modules 50A4 and 50A5, the pressure returned to normal. After removing the 50A4 board and replacing the micro relay, the machine operated normally.
Fault 2
The first set of plate-making motors does not operate, and printing in both the circumferential and axial directions is not possible, although a plate status display appears in the Colortronic window. The Register module 129 was checked, and the 24 V power supply voltage was normal. The monitoring indicator lights during operation, and UR± and SR± are adjustable, but there is no voltage output at the P1 socket.
The potentiometer (1 kΩ) at the P8 plug was measured. The plate motor output current is 4 A with protection enabled. It is suspected that the positioning controller is faulty. After replacing the positioning controller, the plate-making motor operated normally.
Fault 3
There is an alarm sound, but no jogging or operation occurs. The safety circuit and input signals are normal, but there is no brake-holding sound. Relay 99K4 does not engage, and 24Y1 has no power.
The control output board 70A5 (MCIF 23, board number 495052) was checked. The output indicators at X3/7 (main drive brake) and X3/8 (main drive ramp-on) are off, indicating no output signal. Board 70A5 was removed.
It was suspected that a micro relay was faulty, but the relay coil resistance and normally open contacts were normal. Further inspection revealed heat marks on the leads of capacitors C67 and C68. Both capacitors (model 103K100V) were tested and found to be defective.
After replacing them with capacitors of the same specification, the fault was eliminated and the machine operated normally.
Fault 4
When the electrical cabinet power is turned on, there is sometimes a buzzing sound, sometimes no operation, sometimes no jogging, and sometimes no response when pressing forward or reverse jog. Occasionally, when the water roller motor of any unit is switched on, the machine starts automatically and runs for about one hour.
The fault is intermittent, irregular, and difficult to reproduce. Initially, there was no clear direction for troubleshooting. Since 70A4, 70A5, 80A4, and 80A5 are the main control boards (MCIF 23) of the same model, they were interchanged for testing, but the fault remained.
Boards 50A4 and 50A5 (MCIF 22, board number 495001) were then interchanged. When 50A5 was installed in the 50A4 position, the machine ran normally and jogging was normal, but the guards of each unit could not be lifted, and the safety circuit cut off the power. When the boards were returned to their original positions, there was no alarm or jog function, indicating that 50A4 was faulty.
As no spare board was available, the micro relays, resistors, and integrated circuits on the board were checked one by one. It was found that pins 18 and 19 of integrated circuit IC2 (UDN2987A) had poor contact. After cleaning with alcohol and reinstalling the board, the machine could jog normally and the safety circuit functioned correctly after lifting the guards.
It was initially believed that the fault had been resolved. However, after several hours of operation, the machine began running automatically when the water roller was engaged. Measuring the voltage between X7/3 of 50A4 and ground showed approximately 8 V. When a water roller motor group was activated, the voltage increased by about 2 V, and sometimes by 1 V.
After cutting the X7/3 wire, the machine operated normally and the fault disappeared, but the delivery function remained while the individual unit controls were inactive. Each unit's reverse jog switch and DWP12 board were checked one by one. Corrosion traces from old dampening solution were found at the X1 socket of the second DWP12 board.
The resistance between pin 20 (machine inch reserve) and pin 13 (damp roller automatic) measured 450 Ω. Analysis showed that water leakage from the water tank caused droplets to enter the board, leading to long-term corrosion on the rear of the socket.
After cleaning the back of the socket with cleaning agent, alcohol, and a needle, the machine was tested. All functions returned to normal, and the above faults were completely eliminated.