Hi and welcome back to justanswer.From your description , this problem is caused by the main board part # 1AA4B10N22900-J4FJ
This model has had a history of failing main board and the symptoms are exactly what you described.
Also is the only board made by sanyo in this tv , the rest is all panasonic.
You can find it at the address below ;http://www.shopjimmy.com/sanyo-1aa4b10n22900-j4fj-main-unit-for-p50719-00.htm
Just verify that your tv`s model number is XXXXX or DP50719-00