136 E8257D/67D, E8663D PSG Signal Generators Service GuideTroubleshootingOverall Description— The A4 inverter converts dc voltage to the ac voltage required by thedisplay.— A backlight (a bulb powered by the A4 Inverter) lights the display so thatinformation is visible.— The A18 CPU generates data, which is routed to the LCD through theA3 Power Switch assembly.— To extend the life of the LCD, an available sleep mode turns the LCD offafter a defined inactive period (no key presses or program commands) andturns it back on with any key press.RF Output ConnectorOn 20 GHz instruments, the RF output connector is an APC 3.5 male orType–N (Option 1ED). On models with output frequencies above 20 GHz and<50 GHz, the RF output connector is a 2.4 mm male. On models with outputfrequencies above 50 GHz, the RF output connector is a 1.85 mm maleconnector. Option 1EM moves all front panel connectors to the rear panel.Rear PanelThe rear panel contains the power line module, LAN, GPIB, RS–232, and A20Source Module Interface (SMI), scalar interface, and BNC connectors used forsweep interface. BNC and SMB connectors may be present on the rear panelbut not operational if the option associated with that connector is not installed.Frequency GenerationThe YIG oscillator generates frequencies from 3.2 to 10 GHz.OutputFrequencyOscillatorFrequency Path Notes< 250 MHz 3.2 to 10 GHzLowband path,and part ofhighband pathA6 Frac–N signal is mixed with a 1 GHz signal on the A8 output assembly;the difference is used to generate the lower frequencies.250 MHzto3.2 GHz4 to 8 GHz Oscillator output is divided by 2/4/8/16 on the A6 Frac–N assembly.
