The inverter on my 20" iMac G5 (rev. A) has gone bad (it's dimming the screen). What is the best place to get another one? It is not under warranty. I found some 17" inverters on eBay - will those work in a 20"? We Love Macs has a 20" inverter but it's $150 which seems to be quite expensive based on what 20" inverters have sold for in the past on eBay (completed listings). Thanks in advance!