Service Quick Reference Guide - Troubleshooting 3-91The +5 VDC Interlock CircuitThe 5 VDC Interlock Circuit runs from the 5 VDC LVPS to the L/H Door Switch,then to the Engine Control Interface Board, out to the R/H Door Switch, back tothe Engine Control Interface Board, out to the Front Door, through the coil of theLD Power Relay and back to the 5 VDC LVPS. This circuit helps identify whichdoor has interrupted the 24 VDC circuit.If the circuit is complete, LD Power Relay activates, and 5 VDC is sent to theWaste Cartridge Installed Interlock Switch and through all four Print Cartridgeconnectors and to the Engine Control Interface Board. This signal merelyconfirms that all Print Cartridges are installed. Individual missing componentsare identified at power-up or when a door is closed (completing the 24 VDCcircuit) and the Engine Control Board interrogates the Print Cartridge NVRAM. Ifthe Print Cartridges are present, then the Waste Toner Cartridge is missing bydefault.1. With all doors closed and printer power on, check for +5VDC between P536-4of the Engine Control Interface Board and frame ground. If not present, checkthe LD Relay and the LH Cover Interlock Switch.2. Check for +5VDC between P536-6 of the Engine Control Interface Board andframe ground. If not present, check the Front Cover Interlock Switch.3. Check for +5VDC between J568-7 (top pin) of the LD Power Relay and frameground. If not present, check the RH Cover Interlock Switch.4. Check for +5VDC between P536-1 of the Engine Control Interface Board andframe ground. If not present, check the LD Power Relay, and the circuitthrough the Waste Cartridge Sensor and the four Print Cartridge connectors.5. If +5VDC is present, then replace the Engine Control Board (RRP 42, on page7-190).
