Phenomena: Same as above.
Analysis: This fault is a DC power fault. The LQ-1600K printer has two types of power supply boards. The MONPS board works at 100-120V grid voltage; the MONPSE board works at 220-240V grid voltage. The structure of the two boards is almost the same. Therefore, only the MONPSE board is analyzed here. There are the following three power outputs on the power board: +35V, which is used for the carriage motor, paper feeding motor, the drive of the printing head pressing link electromagnet and the fan: +5V, which is used for the control board (MONMA) logic circuit, sensor power supply in various detection circuits, indicator light power supply on the operation panel, paper feeding motor and paper pressing link electromagnet coil locking (maintaining) voltage; ±12V, used for optional interface chips. In addition, there is also a set of Vx (+5V) power supply which is generated on the control panel for the reset circuit, buzzer power supply and the pull-up power supply of the pin data output terminals H1-H24 in the print head drive circuit, which is controlled by the power indicator light If it does not light up, the carriage does not return to the initial position, indicating that there is no ±5V voltage output, and the fan does not rotate, indicating that the +35V voltage has no output.
Processing:
1. After testing, the +35V voltage was normal, but there was no +5V voltage. Further testing found that IC20 was invalid. After replacing it with the original model STR20005, the fault was eliminated and the printer returned to normal.
2. After testing +5V, +35V voltage has no output, further inspection found that resistor R1 is open circuit, so that the c-e pole of transistor VT1 is broken down, and the main switch circuit is damaged, resulting in +5V, +35V voltage There is no output, after replacement After R1 and VT1 (C4313), the printer resumes printing.