I can't guess what spares you have but did you take a voltage reading on the battery inside?
Hi. I have problems - big problems with my Imac 27 inch mid 2011 (bought it used - not functioning). Firstly - when i started the mac there was a box in the middle of the screen with a question mark. Then i tried to make a pram and smc reset, and now the screen is completely black. I then found a thunderbolt cable. Attached the bad Imac to another functioning Imac i have (27 inch mid 2013 model). The I started up the bad Imac in target disk mode. To my surprise there came a mounted disk on my functioning mac. The problem here was, that there were no files on the harddrive - at all! I then installed El Capitan on it. Started the bad Imac again - still black screen. I have then tried to make target display mode to my functioning Imac. It works, and i get picture from my "bad" Imac. What is wrong with it? Is it the display (or how can i find this out?) or is it the graphics card? Why did it go black after SMC reset ?? Someone told me, that isolated it should be the LCD that is failing or the connection to it. ? Please help me