The A board is one of many possible failures, and not the most likely one either. I would not trust a geek squad evaluation, they likely didn't do any specific diagnostic testing and are just making a guess at a common failure. The SC board is more common.
Neither board is all that difficult to replace, but it is more of process of elimination, which gets to be expensive when you are replacing part after part working through the possibilities.
It can be fixed, but the parts are tough to find. You can get the SC board here, which is the first part I'd replace: http://bit.ly/2fdJjRj and the cost is reasonable.
The A board is pretty much impossible to find. If the SC doesn't do it, I'd move on to a new tv at that point. This is a 2012 model and about at the end of life stage anyway, and plasma technology is long obsolete. You'd be better served buying a new LED tv with a fresh warranty in the $400 range than spending almost that much on parts to fix this one.
For either part, it is a simple couple of screws and wiring harnesses to install, just a board swap.
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