The replacement midplane board arrived in a box about the same size as the iMac, plus some padding. It was really nicely packed, with hefty layers of shaped foam holding the board in antistatic wrapping. I’d already warmed up my PowerBook with the pdf of the instruction manual – but that became redundant since they’d included it in the box, along with a UPS return shipping label, spare screws and a magnetised Philips screwdriver. I was impressed by the level of detail here.
The midplane board is essentially the entire logic board, processor, cooling fans, input/output sockets and speakers assembled on one slice of (what I’m assuming is) aluminium. Everything else needs to be removed and swopped over to the new board: optical drive, display inverter, fan cover, airport card, ram chips, hard drive and power supply.
I’m always really paranoid about going inside my computers – components are usually covered in warnings about static electricity, and I’ve got no idea about how sensitive they are and just how careful you need to be. I don’t have an anti-static wrist strap so I just kept grounding myself and trying not to move around on the carpet too much.
I’d put a strip of double-sided tape on a piece of A4 to let me secure and label all the screws, since they all seem to be different, and I’d made sure that I had lots of available surfaces.
So, with the iMac face down the back comes off nicely, and we’re in. First out is the optical drive, followed by the display inverter and the fan cover:
Then the airport card (I couldn’t believe how small it is: looking at the picture in the Apple Store I always thought it would be a decent chunk o’ tech) ram chip, hard disc and power supply.
The hard disc has two chunky connectors for data and power on the left, and a few tiny wires attached by the teeniest connection block you’ve ever seen on the right: uncoupling that was pretty fiddly, since I’m never sure how much force needs to be exerted. The power supply needs to be taken out at an angle, with the top coming out first so the bottom edge can be slipped around the retaining clamp that’s released with the middle case screw: what makes this slightly more difficult than it should be is the very short and inflexible chunk of cables running to its connecting block, which needs to be uncoupled from the midplane at the same time as the PSU is being lifted out.
With the ram chip (very carefully) removed, the six screws holding the midplane board to the front casing come out, and the entire slab is lifted out using convenient pull-tags:
Here the individual parts are laid out on my bed (the only free surface remaining):
[optical drive, fan casing and hard disc along the top; display inverter, ram chip, airport card and power supply on the bottom]
Here’s something you don’t see every day, the inside of the iMac casing with the midplane board removed:
Note the grey panel bottom centre that forms the Apple logo on the front, the flat black video cable running up from the center and the small inverter cable at the top left. You can just about see the clamp on the middle case screw at the bottom that locks the power supply in place.
The new midplane board was a bit of a squeeze to fit into place – it’s a very tightly packed machine, and doing the swop really made me understand how completely integrated the whole system is. This is about as far from an “off the shelf” PC as it’s possible to get, it’s all designed to be one big component.
The only parts of the reassembly process that caused problems were the tiny connector on the hard drive – which is far too fiddly – and fitting the power supply back in. The PSU is held in place with screws held captive in recessed holes, which must be mated exactly with raised screw-holes on the midplane: since the PSU has to be lowered in at an angle with no hand-holds and the connection block needs to be recoupled at the same time, the operation was a little tricky. But possible, after a while.
Ram chips always seem to need more force than they should, given their fragile, static-prone nature, and the optical drive needed a lot of careful encouragement to be reconnected. There was also a screw in the new midplane board where there wasn’t in the old one: this should have held the bottom of the optical drive in place, but since this was a silver rather than bronze screw, I couldn’t remove it without invalidating my warranty. Here it is, the silver screw where a hole should be:
I fitted the back cover on and it’s palpably tighter – verging on not fitting – on the left hand side. The new midplane is probably a leeetle bit out of place, so I’ll take another look at it. I also got to wondering: how does the back stay on? The three screws along the underside of the case don’t actually lock anything – they just pull the bottom of the case up against the back. The whole system seems to be resting mainly on the tabs at the top of the case!
Then, with fingers mentally crossed, I powered her on. Startup chime! Hard disc activity! I breathed an exagerated sigh of relief, but was somewhat taken aback by the “Welcome to Mac OS X” movie and setup assistant that followed the startup process. Once I’d created a new user and logged in the mystery deepened – all my data was intact on the hard drive but I couldn’t access my old user settings. Then I realised that she’d started up from the other OS X installation on a different partition – it must have chosen a startup volume alphabetically, using “Spare 1″ rather than “Tranquility”. Once I’d restarted with the correct volume everything was fine.
During my two days without Tranquility I’d read a few forums about excessive fan noise in iMac G5′s, and a lot of people seem to have gone through a number of replacement midplane’s to solve the problem. I was a little narked to find that my new midplane was distinctly noisier than the old one, with a definite whir to the fans. This has reduced somewhat, but she’s still louder than I remember her. Strange thing is, this board whirs the fans more but doesn’t seem to pump as much air when the processor heats up as the old one.
Whatever. I’m extremely happy that the board-swop worked, that Apple exceeded my expectations in shipping it out to me, that they included great documentation (although it differed ever-so-slightly from the downloaded version), tools, and a return shipping thingie that should collect it straight from my door! Most of all I’m happy to have a machine, and a company, that I can rely on.
But why isn’t the power light working?
