DIY repair your laser printer

A laser printer is a kind of output device which integrates laser scanning technology, electronic technology, electrostatic imaging technology and so on. It has the characteristics of fast printing speed, good printing quality, high resolution, and low noise. It is an important computer peripheral equipment. With the emergence of a network printer, it is widely used in office automation, printing, publishing, scientific research, and other industries.

Typical faults and maintenance methods

Fault 1

The image of a laser printer is obviously black and white on one side. After replacing the toner cartridge and cleaning all the components, the fault still exists.

Maintenance method: through the maintenance of the optical part of the laser printer, the fault is solved. It is mainly to open the shell of the laser printer, disassemble the black plastic box, carefully wipe several reflective surfaces of the multi shuttle mirror with clean lens paper, wipe several optical lenses clean, restore the removed plastic box, and pay attention to the installation of the connector of the junction card. When the machine is turned on again, the printed handwriting will be full.

Fault 2

The laser printer often fails to turn on the heating lamp. Only one power lamp turns on after the machine is turned on, so the machine can not work normally.

Maintenance method: through inspection, it is found that it is not the problem of fuser, power supply or small relay. It’s a problem that a 102J small resistance heated by the tube in a small box beside the power box doesn’t contact the circuit board well. Because it’s two sides of the circuit board, both sides should be welded, and the trouble should be eliminated after the electric ferrochrome is welded. This fault is very common in St laser printer, but sometimes the heating lamp does not work is the one-way SCR fault of power control part. Fusing lamp, thermistor and thermal protector are also common failures. If the measuring fusing lamp tube is burnt out, the thermistor performance is not good, and the thermal protector is open to replace.

Fault 3

Sometimes the heating lamp of the laser printer is on or off.

Maintenance method: when the heating lamp is not on, use a multimeter to check whether the connecting wires of two light tubes are broken or not, and whether there seven thin wires are broken, because the fusing part of the laser printer is connected to the main machine flexibly, and several wires are often disassembled and broken easily. If the heating lamp does not light up frequently, but it can be used normally after a long time of cooling, it is the problem of the thermistor. Replace the thermistor with a new one, and the fault can be solved. Use a multimeter to measure 320K Ω in cold state and 1.45k Ω in the hot state of the normal thermistor.

Fault 4

The output image is light in color, unable to see the handwriting clearly.

The color of the laser printer and the output image is so light that the handwriting can hardly be seen. Try to adjust the contrast knob to the maximum position, and the output sample handwriting is still unclear. Considering the dirty mirror surface, wipe the reflector and focusing lens with alcohol cotton ball, and the fault is still the same. Check whether the transfer electrode wire is normal. If no abnormality is found, clean the electrode wire, and the fault is still not eliminated. Check the charging electrode wire of the powder box. It is intact and normal. Check the high-voltage and high-voltage contacts. It means that the fault is not related to the electrode wire.

Through further inspection, it was found that a spring plate of the sensitive sensor switch of the laser drive circuit was broken, which causes the printer to fail to close when it is working, resulting in the above-mentioned fault. After replacing the spring plate with a new one, the fault is removed.

Fault 5

Photographic fixing heating is not normal

After the laser printer is turned on, the power indicator light is on. The preparation/waiting indicator light is off as soon as it flashes. The fusing heater only flashes once and no longer heats up. Sometimes the fusing heater does not work at all when the printer is turned on.

Based on the fault, suspect the fusing heater is in poor contact or damaged. Take down the fusing heater, use the multimeter resistance to check whether both ends are normal, and check the thermistor, temperature sensor and protection circuit, and no problem is found. Check the control interface circuit of the main control board and no abnormality is found.

Further, check the heating drive circuit and find that there is a problem with the thyristor. After the replacement of the new silicon controlled rectifier, the fusing heater returned to normal operation and the fault is removed.

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