Tag Archives: iMac

Repairing an iMac Power Supply

A 24″ iMac that wouldn’t start up came in for repair.   Pressing the power button got the fan to briefly run then shut off.  It never reached the point where there was a happy (or sad) chime.  The owner’s first inclination was to toss the computer after we wiped the hard disk but I told him we could probably get it running for the cost of a new power supply (around $75).

Using the always great disassembly instructions at ifixit.com, I got the front bezel off the iMac and checked the logic board diagnostic LEDs.  LED 1 was on and LED 2 came on briefly when I tried to start the computer, indicating that the logic board was probably fine and the problem was with the power supply.

Several disassembly steps later I had the power supply board out of the iMac.  From a quick visual inspection, I could see that some of the  2200 µF capacitors were leaking a bit and one had developed a considerable bulge at the base.  Maybe we could do a cheap repair here?

I clipped the four suspicious caps out (to get an accurate measurement) and checked them with my Fluke 179 multimeter–quick side story:  this DMM is so rugged that it survived a total loss house fire with only minor cosmetic damage.  All the capacitors were out of spec but interestingly the one that looked the worst actually measured closest to good.

Easy peasy fix, right?  LOL, not exactly.  This board uses lead free solder, which is a total pain to remove.  Even with my trusty Hako soldering iron cranked up to 800º, the PCB’s heavy copper traces made it a challenge to keep the solder molten long enough to suck it up with a desoldering tool.  An hour of determined effort and cussing later I had the old caps out and the through holes cleaned out.  (I needed to ream most of the holes to get the last bits of lead free solder out).  Four new shiny black capacitors installed without any drama.

Shiny new capacitorsAll LEDS Normal

I reinstalled the power supply module and the iMac started normally with 4 LEDs lit on the logic board.  I also installed a new button battery while the iMac was open.  Total cost of repair: under $2 🙂

If I were to attempt a similar repair again I wouldn’t bother with trying to remove any components from the circuit board because of the lead free solder.  The job wouldn’t look as pretty, but it would be a lot easier to just leave the old leads in place and solder new parts onto them.

A month of many Macs

iMac glass panel

The 500 GB hard disk in my friend’s circa 2008 24″ iMac started making ominous clicking noises last week.  Anticipating its near future death, we took a full backup and ordered a bigger 1 TB drive from Amazon.

Apple never ceases to amaze me with the variety of ways they find to hide fasteners (and make upgrades and repairs to their equipment nightmarishly difficult).  In the case of this iMac, one needs to remove a glass panel held on with magnets to gain access to the internals.  The panel can be removed with a couple of these fancy suction cup tools but I prefer to do it ghetto style with a couple of sink plungers.

After pulling off the glass panel, removing around three dozen screws of at least eight varieties, and unplugging several needlessly fragile connectors, the display panel can be removed and the iMac’s guts are exposed.

iMac Guts

The actual hard disk swap is a walk in the park.  Reassembly brings one extra reward.  The combined effect of the glossy LCD display behind the glossy glass cover is a fingerprint magnifier that exceeds the capabilities of the world’s finest CSI labs.  It took six [expletive deleted] install/test/remove/clean cycles to get a smudge free display.  Thanks Apple.