HP LaserJet 4 Service Manual - Page 56

Service Mode (Refer to Appendix B for LaserJet 5 information.) The Service Mode should be used only by authorized service personnel. The following can be executed while in the Service Mode: • Print a Service Mode Self Test. • Verify the Page Count, (the page count also is displayed on the standard self test). • Set the Page Count. • Set the Cold Reset Default (This sets the factory default paper size. Use when replacing non-U.S. Formatters). • Set the Diagnostic Functions ON or OFF (for software developers use only). • Demo Page=On/Off. Removes the Demo Page option from the self test menu. • BIG Data=On/Off (HP LaserJet 4 Plus only). Setting BIG Data to ON increases the size of the printer's status Readback Buffer. The following procedure is used to initiate the Service Mode. 1 Hold down the [ON LINE], [FORM FEED], and [ENTER] keys while powering ON the printer, until the ON LINE and FORM FEED Indicators are both illuminated and the Display Window is blank. (If the Display Window reads 05 SELF TEST at this point, the keys were released too soon. Repeat this step until successful.) 2 Press the [FORM FEED] key, then the [ENTER] key. The message SERVICE MODE is displayed briefly, then the printer automatically begins a 05 SELF TEST. After several seconds, the [ON LINE] and [FORM FEED] lights turn OFF. (The printer may display 02 WARMING UP if it has not warmed up completely.) After the printer has warmed up and passed the self test, SERVICE MODE is displayed. To exit the Service Mode press the [ON LINE] key. 3-20 Configuration