LC-42X20E (serv.man4). Troubleshooting Table - Sharp TV Service Manual (repair manual). Page 21

LC-42XL2E/S/RU, LC-46XL2E/S/RU, LC-46X20E/S/RU, LC-52XL2E/S/RU, LC-52X20E/S/RU

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SCART2:                             
No picture from EXT1 appears on EXT2-connected monitor.

NOTE: Normally, if the screen during display is sent to EXT2, no picture is sent to EXT2.

                                            
Checklist:
1) Is the Signal Type (item) in MENU-Option-Input Select equal to Signal Type of an external device? 

⋅ ⋅ ⋅ Set it to “CVBS”, “Y/C” or “RGB”.

2) The picture is sent to the monitor in a CVBS signal if the source during display is TV, CVBS or Y/C of EXT1-3.

When sent by component, etc., that signal is not sent to the monitor.

3) When the monitor picture is not sent and is not displayed on the monitor, refer to “No picture” for each terminal.
4) The video output from EXT1 is not the monitor output (output of the picture now watching).

The picture of the last selected TV channel is always sent to EXT1. (Specification)

TERMINAL UNIT:                 
Is CVBS signal input from pin (51) of IC506 to pin (19) of 
SCART2 (SC503)?

YES

Check the setting of an external input device that connects of 
SC503.

NO

Is CVBS signal sent to pin (65) of IC506 (VIDEO_SELECTOR)?

YES

Check the IC506 and its peripheral circuits.

NO

Is CVBS signal sent to pin (20) of SCART1 (SC502)?

YES

Check the line between S502 and IC506.

NO

Check the setting of an external input device that connects of 
SC502.