HP LaserJet 4 Service Manual - Page 255

14 NO EP CART Message The printer detects the presence of the Toner Cartridge and the level of toner present in the cartridge through the condition of the ANTIN signal. The ANTIN signal becomes part of the serial data stream used to communicate with the DC Controller (see Figure 7-5 for cartridge components). Troubleshoot the 14 NO EP CART (or INSTALL TONER CARTRIDGE) message as follows: 1 Reseat the Toner Cartridge. Try a new or known good Toner Cartridge. 2 Check the High Voltage Contacts for damage. If the contacts are dirty or damaged, clean the contacts after the repair. 3 Replace the High Voltage Power Supply. 4 Check and reseat the HVPS cable. 5 Replace the DC Controller. 16 Toner Low Message The TONER LOW message results as the level of toner in the cartridge cavity falls past the minimum level. The level is sensed by a mechanism similar to an antenna, which detects the AC Developer Bias Voltage applied to the developer mixture. If the TONER LOW message cannot be cleared by shaking or replacing the Toner Cartridge, perform the steps listed for troubleshooting the 14 NO EP CART message. Troubleshooting 7-25