E8257D/67D, E8663D PSG Signal Generators Service Guide 135TroubleshootingOverall DescriptionLine ModuleThe line voltage connects to the power supply through the A22 Line Module.Because the power supply automatically detects and adjusts to different linevoltages, manual line voltage selection is neither necessary nor available.Power Supply Thermal Sensors and fansTwo thermal sensors prevent the signal generator from overheating. Onesensor is internal to the A19 Power Supply; the other sensor is on the A8Output. If the signal generator goes into thermal shutdown, the amber andgreen LEDs on the front panel blink on and off.There are two fans in the instrument. One fan cools the power supply. Theother is a variable speed fan that increases and decreases its speed to regulatethe instrument’s internal temperature. For reliability, it is important to operatethe instrument with the covers installed to ensure proper airflow and cooling.Input/Output InterfaceFront PanelThe signal generator accepts inputs through the front panel hardkeys and thedisplay softkeys, and provides outputs on the front panel display, and throughthe RF output connector. Depending on the model, features, and options, thefront panel may have modulation input/output BNC connectors installed butnot operational if the option associated with that connector is not alsoinstalled.When line voltage is present and the signal generator is in standby mode, theamber LED above the power switch lights. When the signal generator is inpower–on mode, the green LED (also above the power switch) lights.Hardkeys/SoftkeysThe front panel has two types of keys:Hardkeys are dedicated to specific functions, entering values for the mostcommonly used features, and controlling the display’s contrast and intensity.The front panel keypad uses a row and column configuration. Pressing a keymakes a connection between a row and column. The row and columninformation is routed to the A18 CPU where it is interpreted, and thecorresponding function executed.Softkeys, located along the display, are used to select the function displayedto the left of the key (on the display). When a softkey is pressed, the displayedfunction changes.A2 DisplayA liquid crystal display (LCD) provides information about the instrument'ssettings and condition. The LCD requires a power supply, lighting, and data:
