WD-73737 Can't configure

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I refurbished a 73 inch Mitsu recently but am now have problems with getting it to work properly. Here's the situation. Works fine when an over the air antenna is hooked up. Works fine when a game console is hooked up through the HDMI cable. BUT when I go to connect it to a cable box through the composite connection OR the HDMI port, I get audio but no video. I also do NOT get any display of the MENU. I fear it is in "game mode" or something that will not let me change the inputs.



I have "reset the set" by. holding down the power button for 20 seconds or so on start up. No change.



How can I invoke the SERVICE MENU?



I suspect it's a problem with MITSU's "auto device detection" system. Any help would be most appreciated.