Hi there and welcome to Just Answer. Thanks for asking your question.
Sounds like the lamp ballast. Did the previous lamp blow or just go dim over time?
The previous lamp blew. This is the third time I've replace the lamp in 4 years which is okay but this time it started doing this. Is the lamp ballast something I can replace myself?
Wow. Three times in 4 years is not normal unless the TV has been used an extremem number of hours. It should last 2000-3000 hours average.
The ballast is here: http://www.partstore.com/Part/Toshiba/Toshiba/62HM84/Toshiba/Toshiba/23122468/Refurbished.aspx
Replacement isn't too hard, you would need to remove the back off the TV and locate the existing ballast board. Unplug it, unscrew it and install the new one.