HP 2500 L Service Manual
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EN 4 Theory of operation69 Photosensors and switches Figure 17.Photosensors and switches Figure 18. Photosensors and switches 1 23 4 5 6 7 Table 17. Photosensors and switches Reference Description 1 Tray 1 sensor 2 Roller-engaging sensor 3 Developing-rotary-engaging sensor 4 Fuser-delivery sensor 5 Front fuser detection sensor 6 Door-open detection switch 7 Power switch
70Theory of operation C9706-90926 Solenoid and clutches Figure 19.Solenoid and clutches Figure 20. Solenoid and clutches 1 2 3 4 Table 18. Solenoid and clutches Reference Description 1 Developing-rotary-stopper solenoid 2 Tray 1 pickup solenoid 3 Roller-engaging clutch 4 Registration clutch
EN 4 Theory of operation71 Printed circuit assemblies Figure 21.Printed circuit assemblies Figure 22. Printed circuit assemblies 123 4 5 78 96 Table 19. Printed circuit assemblies Reference Description 1 Developing-rotary/toner-level detection PCA 2 Transfer-belt home-position detection PCA 3 Density-detection PCA 4 Waste-toner-detection PCA 5 Registration-detection PCA 6 Dc controller 7 Sub high-voltage power-supply PCA 8 High-voltage power-supply PCA 9 Power supply
72Theory of operation C9706-90926 Image formation system The image formation system, which forms a toner image on media, consists of several interdependent systems: electrostatic latent-image-formation system developing system transfer block fuser ITB cleaning block imaging drum (with ITB) photosensitive drum Figure 23. Image formation system
EN 4 Theory of operation73 Image formation process Laser printing requires the interaction of several different technologies including electronics, optics, and electrophotographics to provide a printed page. Each process functions independently and must be coordinated with the other printer processes. Image formation consists of the following five processes: 1Latent-image formation 2 Developing 3 Image transfer 4 Fusing 5 Transfer-belt cleaning The five processes are divided into twelve steps, which are shown in figure 24 and described in the following sections. Figure 24. Image formation process
74Theory of operation C9706-90926 Latent image formation stage Step 1: primary charging A dc bias is applied to the primary charging roller, which transfers a uniform negative potential to the photosensitive drum. Figure 25. Step 1: primary charging Step 2: laser-beam exposure The laser beam scans the photosensitive drum to neutralize negative charges on parts of the drum. An electrostatic latent image is formed on the drum where negative charges were neutralized. Figure 26. Step 2: laser-beam exposure
EN 4 Theory of operation75 Developing stage The developing cylinder comes in contact with the photosensitive drum to deposit toner onto the electrostatic latent image. NoteThe charges on the exposed area on the drum are shown as positive in figure 27. The charges are actually negative, but they are more positive than the charges on the developing cylinder. Figure 27. Developing block Step 3: developing Toner acquires a negative charge through friction from the developing cylinder and the blade. When the negatively charged toner comes in contact with the drum, the toner adheres to the electrostatic latent image. The image on the drum becomes visible because of the toner. Figure 28. Step 3: developing
76Theory of operation C9706-90926 Transfer stage Step 4: primary transfer The primary transfer roller, to which a dc positive bias is applied, imparts a positive charge on the transfer belt. The negatively-charged toner on the drum is transferred to the positively-charged transfer belt. This procedure is repeated for each color (yellow, magenta, cyan, and black). The dc positive bias is increased for each successive color to make sure that all of the colors adhere to the transfer belt. Figure 29. Step 4: primary transfer
EN 4 Theory of operation77 Step 5: secondary transfer The secondary transfer roller, to which a dc positive bias is applied, imparts a positive charge to the print media. When the print media comes in contact with the transfer belt, the toner is transferred to the print media. NoteWhen secondary transfer is complete, a dc negative bias is applied to the secondary transfer roller to prevent toner on the transfer belt from adhering to the secondary transfer roller. Figure 30. Step 5: secondary transfer Step 6: separation The elasticity of the print media causes its separation from the transfer belt. A static charge eliminator aids separation by weakening any electrostatic adhesion. Figure 31. Step 6: separation
78Theory of operation C9706-90926 Fusing stage Step 7: fusing The dc negative bias applied to the fusing film strengthens the holding force of the toner on the print media and prevents the toner from scattering. Figure 32. Step 7: fusing Step 8: roller charging (auxiliary ITB cleaning roller) During secondary transfer, not all of the toner on the transfer belt is transferred to the print media. Toner that remains on the belt is called “residual toner. ” The auxiliary transfer belt cleaning roller, to which a dc positive bias is applied, imparts a positive charge to the residual toner, strengthening its hold on the transfer belt. This prevents toner from falling off of the transfer belt, scattering in the printer. Figure 33. Step 8: roller charging (auxiliary transfer belt cleaning roller)