The iMac is one of the best desktop machines in Apple's history, and can be broadly split into two major groups. To be technical, the thick ones and the thin ones! The thicker, earlier models shipped with built-in DVD drives and often had common graphics card issues. Thankfully, these problems are absent in the later, thinner models.
iMacs are listed below oldest to newest.
iMac 24" 2008
GPU failure - A significant number of these machines were shipped with a particularly poor graphics card (the NVidia 8800GS) which had a high failure rate. A failed card can manifest in several ways - incomplete booting, display failure or displaying graphical artefacts. As virtually no other card is compatible with this machine, direct replacement with a working legacy NVidia 8800 GS is not recommended for obvious reasons. A repair is sometimes possible, but given the age of the machine, it's not often economically viable.
iMac 21.5" & 27" late 2007 - 2011
GPU failure - A significant number of these machines were shipped with a particularly poor graphics cards which had a high failure rate. A failed card can manifest in several ways - incomplete booting, display failure or displaying graphical artefacts. Many of these machines have dedicated graphics card, so direct like-for-like replacement with compatible legacy cards is not recommended for obvious reasons. A repair is sometimes possible, but given the age of the machine, it's not often economically viable.
LCD failure - This issue is more prevalent in the 27" models, and manifests as either not powering on at all or screen blanking during operation. Screen replacement is possible.
iMac 27" 2012
Intermittent power down - This can have several causes, most commonly a faulty power supply and/or a failing logic board. This issue requires inspection, but can often be repaired.
iMac 21" & 27" 2013 - 2019
Drive failure - This affects machines that were shipped with either conventional hard drives (HDs) or Fusion drives (FDs). HDs were slow by SSD standards, but FDs, which used a hybrid HD and SSD design could often be even slower. The relatively small SSD portion of an FD is used by Mac OS as a commonly accessed data cache, so degrades very quickly. The best remedy is replacing any existing drive with an SSD. Please contact us with your iMac serial number.
If you're experiencing a problem with your iMac, please contact us at MacKing. We exclusively use genuine Apple parts, and pride ourselves on being cost effective, fast, efficient, and, of course, friendly. If it can be fixed, we'll fix it.
Thinking of buying an iMac from new? Think different.
Apple are working hard to reduce their carbon footprint, but computer manufacture is notoriously carbon and rare earth heavy - not to mention the sumptuous packaging. Be kind to your planet and your wallet and choose the tech Fair Trade option - buy refurbished.