Pioneer PDP-5080HD Manual

try a full factory reset then check to see if someone has turned on the mode or channel block, some tv,s you can block the dvd mode through the parental guide lock

Lay the TV on a soft flat surface, then you just have to remove the stand and all the screws on the back, then the board mounting screws and connectors. Best thing to do is to take a lot of pictures so you will know how it goes back together. Mark the connectors with marking pen also.
Also look for any bad caps with domed tops when you are at it as well.
Boards:
http://www.shopjimmy.com/catalogsearch/result/?q=Pioneer+PDP-5080HD

Basic LCD monitor and TV troubleshooting guide:
http://www.fixya.com/support/r5093881-lcd_flat_panel_tv_troubleshooting_guide
http://www.fixya.com/support/r6150077-basic_lcd_monitors_troubleshooting
http://www.fixya.com/support/r7406380-tv_training_manuals
Failed TV and Monitors pictures: http://s807.photobucket.com/albums/yy352/budm
Learn about bad caps: http://en.wikipedia.org/wiki/Capacitor_plague
Parts: www.shopjimmy.com
Parts: http://interliquidparts.com/

Capacitors kit: http://lcdalternatives.auctivacommerce.com/Default.aspx he can make you a set of caps.
Or www.digikey.com, just make sure to use caps with low ESR, 105c, high ripple current and long life rating such as PANASONIC FM or FC series.

My research into your set and its TV Guide feature brought up two points that may be relevant:

1. It apparently takes about 24 hours for the guide to load up completely. This would make it difficult to get real-time info as to whether it was working or not.
2. 'TV Guide' may not work will all providers, and may not work as providers switch to digital. Have you spoken to your provider about possible compatibility?

I hope that helps
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Click here for a Pioneer PDP-4280HD manual.

where is the video feed coming from? did you try a diffrent cable? can you change the channel at all?