Lexmark W820 Service Manual - Page 70

4025-Finisher General Notes on Using Service Checks • Unless indicated otherwise, the instruction "switch ON printer main power" means for you to switch ON printer power and let the printer proceed through power-on diagnostics and warm-up until it is online and ready to print. • Conventions used to represent connectors: • P/J XX means a Plug and its corresponding Jack are connected. • PXX means a Plug is disconnected. (Unless this plug is soldered to a board). • JXX means a Jack is disconnected. (Unless this jack is soldered to a board). • When you are instructed to take a voltage reading between "P/J A-B and P/J X-Y," place the red probe (+) of your meter on pin B of P/J A, and place the black probe (-) of your meter on pin Y of P/J X. • When you are instructed to take voltage readings between "P/J X and P/J Y" (without specified pin numbers), check all voltage carrying pins. Refer to the Wiring Diagrams for signals and pin numbers. • When you are instructed to take a voltage reading, the black probe (-) is generally connected to a pin that is either RTN (Return) or SG (Signal Ground). You can substitute any RTN pin or test point in the printer, and you can use FG (Frame Ground) in place of any SG pin or test point. • Unless a Service Check instructs you otherwise; before measuring voltages, make sure the printer is switched ON, the Print Cartridge and the Paper Cassettes are in place, and all of the interlock switches are actuated. • All voltage values given in the Service Checks are approximate values. Actual measured voltages may vary more than 25% from the values stated in the Service Checks. The main purpose of most voltage readings taken in the Service Checks is to determine whether or not a FRU is receiving the correct voltage value from the power supply and if gating (a voltage drop) occurs during FRU actuation. Gating signals may be nothing more than a pulse, resulting in a momentary drop in voltage that may be difficult or impossible to read on the average multimeter. • Service Checks may instruct you to remove or replace a FRU. See "Removal and Replacement Procedures" for information on how to remove and reinstall a FRU. • When a Service Check instructs you to replace a FRU, and that FRU is part of a larger assembly, you should replace the entire assembly. 2-10 Service Manual