dp50747 turns on then back off after 20 sec
what is the board marked alarm signal and does that have something to do with my tv turning off by itself
Check the manual available here I am not sure if you already checked the power failure circuit. This unit is equipped with a power failure detector function and will turn your unit of to protect from further damage. Good Luck. Also check Sanyo DP50747-01 no video or sound?
Depending on the chassis version and whether the TV restarts again after it shuts off that could lead to completely different boards.
On the plasma versions of DP50747 made with Samsung display this is usually the main sustain board and the two buffer boards, which are definitely the most common failure for the trio. When they are bad the TV will simply shut off without ever starting and it will stay shut.
In the DP50747 plasma versions with LG displays this is usually one of the two sustain boards and sometimes the YSUS buffer boards as well, althoigh not as commonly as with the Samsung versions. The TV would still stay shut once it shuts off.
For both plasma versions there are also occasional, albiet less common, failures on the power board, which may lead to similar behavior or , for example, the TV running OK for a short while and then shutting off; it may then refuse to come on again for a while (if you try it) and then sometimes it might.
In the LCD variants of DP50747 it could be the main board; when so the TV would fall into a cycle powering on , staying on for 15-20 seconds, shutting off and then powering on again in 1-2 seconds...and looping like that.