LG TV 50PQ300:'Keylock on' .Cannot select 'set up' or 'input'.only AV1 works. Can anyone help please???

The 27" TV uses the same instructions as the 20", and I found the manual for you at the link below. Answering your question directly, here is the section of the instructions about changing input:
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Changing the TV's Input Normally, your TV displays the signal coming through the antenna terminal. However, if you've connected another component to your TV(such as a VCR & DVD) using the Video/Audio input,you will want to be able to view the signal from the component.To do this, you will need to switch from the ' TV ' input to the 'AV1-AV3, CVI' Input, as follows. 1 With the TV on, press the MENU button twice, then " Set-Up " menu will appear. 2 Use the WCHV buttons to select " Input ". 3 Press the CVOLB buttons to change the input source from ' TV ' to 'AV1, AV2, AV3, CVI'. 4 Wait 20 seconds, or press DISPLAY button or MENU button to return to normal TV viewing. * CVI means the Component Video Input (Y/ PB/ PR) from the DVD player etc.* Users can also select these input modes with the TV/AV button or the INPUT button on theremote controller. * On the AV1 mode , if you connect the S-VHS jack to your TV, "AV1" is changed to "S-VIDEO".
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The link to the manual is below.

All sound should go directly from its origin to the sound systm. All video should go directly from the source to the TV if it has enough inputs. NO signal ever benefits from unnecessary routing and cabling to or through a device that neither uses nor improves it.

Hint: TV's don't improve the sound or even need it if you have a hi-fi..

Make sure that the source input is set correctly. You can select the different "source inputs" using your TV remote. For example, if the cables from the cable box going to your TV are going into AV1 port on your TV then you need to select AV1 as the "source input" on your TV settings. This works the same with HDMI1, HDMI2, ect.

looking at the online manual - see link below there are a number of ways to connect that device to a TV

1. Component Video Out
2. S-Video Out
3. Composite Video Out

Now depending on which Input you are using on the TV, you will need to select the input on the TV, often refered to as AV1, AV2, AV3 etc
Comment back on

• which output you are using from the DVD
• Which input you are using on the TV
• Make and Exact model of the TV

There is an online manual available from here http://www.lg.com/us/support/product/support-product-profile.jsp?customerModelCode=DR787T&matchedModelCode=1000002469&searchEngineModelCode=DR787T&initialTab=documents&targetPage=support-product-profile

seems like its the inverter thats either not working or the tubes are faulty

There should be a button on your TV remote that will be called "Display" or "P in P".
The display button usually displays which input you have selected, such as: SAT for Satellite; AV1, AV2, AV3 or AV4 - depending on how many inputs your TV has, to plug in devices like a VCR or DVD recorder/player.
Otherwise, if you have a more sophisticated TV, it could be that you have accidentally pressed the "P in P" button, that selects the Picture in Picture mode. If you have done this, your TV will display the main picture of the input you have selected, plus another input, (such as SAT or AV1 or AV2 etc. as I've mentioned above). If the AV1 or AV2, etc. input is not active (not switched on) then that input will only display a blank (black) picture in the top left corner of the screen.
Hope this helps...

I have a LG tv set. When i press the tv/av button on the remote my tv shows av1, av2 earlier but now it is showing only av. So i am unable to watch my dvd player. Need help.

its an input message i dont have your remote in front of me but im going to say when you hit the input av1 av2 there should be a button on remote for display or info one of these buttons should deactivate that message

What device is connected to TV: cable, sat box, dvd player? What type of cable are you using to connect to the accessory device?

For a red, white, and yellow cable:
I cannot hear sound from the television when connecting to the AV1 input. What do I need to do?
Answer When you connect the accessory device to the AV1 input of the TV using either component video cables (YPbPr) or composite video cable (Yellow), you must connect the audio output from the accessory device to the 'INPUT AV1 AUDIO L R' of the TV using the RCA audio cables (Red and White).
If the connection is good,

Check to ensure that the AV1 audio source from the TV on-screen menu is selected to AV1.

1. Press the 'MENU' button on the remote control.
2. Press the cursor up/down to select SETUP and press the cursor right.
3. Press the cursor up/down to select SOURCE and press the cursor right.
4. Press the cursor up/down to select ANALOG AUDIO IN and press the cursor right.
5. Press the cursor up/down to select AV1 and press the 'OK' button.
6. Press the 'MENU' button to exit the menu.

Make sure that the volume on the TV and on the device is set at an audible level and also that the sound hasn't been muted.

For HDMI,
The picture quality is good but the TV does not produce any sound when connected to an accessory device with an HDMI to HDMI cable.

Answer

• The TV's behavior is considered to be normal as some accessory devices have an HDMI audio output setting that requires to be turned on when using an HDMI to HDMI connection.
• Check the on-screen menu of the accessory device to ensure that the HDMI audio output is set to ON.
• In some cases, you may need to set the digital out audio stream of the accessory device to PCM.
• For detailed information, please refer to the user manual of the accessory device.

Unhook the dvd cables from the AV1 ports on the tv. Then hook these DVD outputs to the inputs on the vcr. Then hook the vcr outputs to the tv inputs (AV1). The tv and the vcr must then be set to channel 3 in order to watch the dvd (and possibly also some menu settings such as setting everything to "component video" and/or setting the tv/vcr button to "vcr. Also set all "3 or 4" switches on the back of all equipment to channel 3. Also, don't forget to go into your tv menu and choose AV1 when you want to watch the dvd and/or the vcr.
You can also try connecting your dish to the vcr and then the vcr to the input on the tv where you HAD the dish connected. There are several combinations you can try, but just remember to always put output cables to the INPUTS of the next piece of equipment in line, and set your menu settings appropriately on all equipment whenever you change from one machine to the next.
If all this fails, then here is a 100% positive solution. Buy an "A/B" switch. It has two inputs and only one output. You could leave the dvd connected as is and connect the dish and the vcr to the two inputs on the A/B switch. Then hook the one output of the A/B switch to the tv. When you change the position of the A/B switch back and forth, you will be changing over back and forth from dvd to vcr. You can move the A/B input selection switch manually or you can buy a remote controlled A/B switch and do your switching with the remote that comes with the switch.
Keever