It could be in the power supply, open the unit up and find the power supply. Look to see if there are any caps that are bulging on top. If they are, they need to be replaced. Look to see if any components are burnt or look like they have got hot. If you know how to use a meter check the values of the resistors and any transistors that just does'nt look right. Check for bad solder joints. If a solder joint looks dull it may be suspect. Hope this is helpful. Ps: replace all components with the same value, this is if you understand a little about electronic.