HP 4550 Service Manual - Page 129

Paper size detection The paper size and the presence of the cassette are detected by the paper-size detection switches (SW801, SW802, and SW803). The combinations of paper-size detection switches are listed in Table 5-5. Table 5-5 Paper size detection switches Paper size Cassette paper-size detection switch SW801 SW802 SW803 Legal OFF OFF ON A4 ON ON ON Letter OFF ON ON Executive OFF ON OFF B5 ON ON OFF B5-ISO ON OFF OFF A5 ON OFF ON No cassette OFF OFF OFF Fusing and delivery unit The fusing motor (M1) drives the fusing assembly, and the paper delivery rollers. Paper separated from the ITB is fed into the fusing unit, and output from the fusing unit by the upper and lower fusing rollers and fusing delivery roller. The paper output from the fusing unit is then detected by the delivery unit paper sensor (PS7). The pressure release sensor (PS6) detects when the fusing roller pressure is off. The printer uses a deflector to switch between the face-up bin and face-down bin. When the face-up bin is open, the paper is delivered to the face-up bin. When the face-up bin is closed, paper will be delivered to the face-down bin (see Figure 5-31). If the face-down bin becomes full, it is detected by the face-down bin paper full-sensor (PS9). Figure 5-31 Fusing and delivery unit C7085-90921 Chapter 5 Theory of operation 127