HP LaserJet 4 Service Manual - Page 248

12 Printer Open Message The 12 PRINTER OPEN (or CLOSE PRINTER COVER) display tells the operator to close the printer's top cover. The DC Controller detects the Printer Open condition through the position of SW601, which is located on the Paper Feed Assembly PCA . A tab underneath the top cover Door engages SW601 through a slot in the Top Cover Assembly. In addition to signaling that the top cover is open, SW601 enables the +24B VDC which controls the high voltage for the printing processes, and the AC Voltage for the Fuser Assembly. Table 7-6 12 PRINTER OPEN Checks Checks Action Is the Top Cover Assembly open? Ensure the Top Cover Assembly is firmly closed, and that the protrusion that engages the switch actuator is not broken. With the top cover open, check that the switch actuator does engage the switch. Use a slim object to manually engage SW601. Listen for a definite "click" as the switch is engaged (see Figures 7-2 and 7-14). Has the Paper Control PCA on the Paper SW601 has an actuator that can be Feed Assembly been replaced? deleted during reassembly. Ensure that this actuator is installed correctly. Is the DC Controller PCA defective? Measure the 24 VDC on J201, pins 8 and 9 on the DC Controller (see Figures 7-16 and 7-17 for locations). If this 24 volts toggles as SW601 is activated, replace the DC Controller. If it does not, replace the Paper Control PCA or the cable. Also check J201-6 (DOPEN). This voltage should be 5 VDC when the printer is open, and 0 when the printer is closed. If not, replace the DC Controller PCA. 7-18 Troubleshooting