HP Color LaserJet 8500 Service Manual - Page 181

Pick-up/feed For cassette paper pick-up, the paper is sent into the printer by the pick-up roller, then fed by the feed roller. After the registration roller corrects the skew of the paper, the paper stops. The paper is then refed so that its leading edge will match the top of the image on the transfer drum. After that, the paper is fed through the transfer, separation, and fusing/delivery units to the top (face-down) or the left (face-up) output bin. The printer switches the speed at which the paper is fed for different media types as indicated in table 34. Table 34. Feed speeds based on media type Modes Feed speed Plain paper Normal speed Glossy or heavy media OHT 1/3 of normal speed 1/4 of normal speed The controller board switches the feed speed when the registration roller paper sensor detects the paper. The printer has two overhead transparency sensors (PS1801 and PS1802, see figure 57 on page 184), and the controller board always monitors these sensors. Automatic overhead transparency detection The printer enters overhead transparency (OHT) mode when the user selects to print on transparencies through the printer driver or by selecting OHT as the media type at the printer control panel. The OHT sensors (PS1801 and PS1802, see figure 57 on page 184) are installed in front of the registration roller to detect transparencies even if the user has not set the media type at the printer control panel. The controller board monitors these sensors to execute OHT detection. PS1801 and PS1802 consist of light emission and light reception units. When a transparency is used, the light emitted from the light emitter unit goes through the transparency and is received by the light receptor. As a result, the controller board determines that the fed media is a transparency and enters the OHT mode. EN Paper path 179