HP 8550mfp Service Manual - Page 150
Secondary transfer, s to eliminate excessive charge build up on the transfer belt.
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7. Secondary transfer The paper is pressed against the transfer drum when the transfer belt press clutch (CL4) pushes the transfer belt up to the transfer drum. Positive DC bias is applied to the transfer belt to transfer the toner that is on the transfer drum surface to the paper. The positive DC bias value changes according to the paper type (such as plain, heavy, or overhead transparency) and environmental conditions. Because the transfer belt is highly resistive, the potential bias is reversed between pages to eliminate excessive charge build up on the transfer belt. After a jam, negative DC bias is applied to the transfer belt to transfer any residual toner from the transfer belt. The residual toner moves back to the transfer drum, and is then collected in the waste toner case in the imaging drum. Figure 31. Secondary transfer 148 Chapter 5 - Theory of operation EN
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