Author: ChrisRand

#chrisRand

This macMini was bound for the e-waste collection but first made a pit stop at my workbench so that I investigative and tear it down. My intent was to learn about how this compact computer was engineered, how dissimilar materials are used, how are parts joined together.

The first place to begin is to locate the main chassis screws that hold the shell together. Normally, the screws would be directly visible in the back of the device or concealed under some kind of rubber bumper or pad on the bottom. I peeled back the bottom pad and found nothing ! Was this going to be a tedious process like solving a master-level puzzle ?

Knolling : the top surface and side chassis. Galvanized steel sheet has been laser cut or stamped and then brake-formed for the top and bottom panels of the macMini. The steel serves 3 major functions; to strengthen the injection molded plastic panels, to create clips for fastening the sub-assembly to the aluminum chassis, and an integrated safety switch. If the plastic top panel is removed for repair or service, the neutral path of electricity is interrupted and prevents the unit from powering up.

I wanted this to be a non-destructive process as if I was a repair technician and i quickly learned that. . . . . YES ! this IS a masterful puzzle to completely disassemble. The example below is from the disc drive mechanism that pull the disc in / out of the chassis.

STEP 1 : rotate metal piece to expose the white plastic part below.

STEP 2 : slide the plastic part back and forth.

STEP 3 : notice or identify that there is an access hole only when the part is in a specific position.

STEP 4 : remove the screw that holds this component.

In addition to standard and custom mechanical fasteners, there were many cleverly concealed means of joinery like  CLIPS, TABS, RIVETS, SPOT WELDS, and some that I’d call mortise and tenon. The engineers wanted to use minimal screws for aesthetics for the exterior of the MacMini but why did they use so few screws on the interior? Do screws take up more time in manufacturing and assembly or are there other ways to solve fastening?

Instead of using 4 screws to hold a part, there would be one or two used in conjunction with tabs, clips or tenons. I found that neighboring assemblies would hold one-another in place. What can we call this methodology. . . . screw sharing?

Creating something that is brilliantly simple often requires more effort.

The injection molded ABS plastic internal chassis was engineered to serve many functions ;

• a skeletal structure that holds the hard drive, most of the PC boards, and the fan.

• integrated ducting to circulate cool air around the device.

• integrated wire conduits, wire clips, and acts as double insulator protecting electrical wires from areas of increased heat.

I was delighted to find that the DVD drive was filled with good old mechanical components used to actuate motion like springs, hinges, motors, gears, linear actuators, and worm shafts.

VIBRATION control : what a delight to discover that the audio speaker was isolated from the chassis with medium density rubber which allows the music to bump/bump and sound clear at high decibel.

PART IDENTIFICATION : Throughout the teardown, I thought about reusing some of these fascinating parts in a future Arduino project, like the LED board. In order to understand how to use it, I search ElectronicProducts.com and discovered how every part is specifically called out including the material, manufacturing process and physicality. The wire harness, mounting bracket, connector, and the black foam rubber pad (die cut w/PSA) are all specified. Below is how just the PCB assembly was called out;

• Location- LED PCB Assembly
• Function- Mechanical / Electo mechanical
• Component Family – Electro mechanical
• Component Type – PCB
• Quantity – 1
• Manufacturer – OKI
• Part Number – NA
• Component Description- 2 Layer – FR4
• Markings- 0507, 01-01003029-00, HH. LED BOARD, CK66 94V-0
• Form- NA
• IO / Pin Count- NA
• IO Pitch- NA
• Diameter (mm)- 10.45
• Length (mm)- 8.70
• Height (mm)- 0.50
• Data Sheet Links- Visit URL

SUMMARY : similar to reverse engineering by way of a 3-dimensional schematic, this was an exciting and fascinating activity. I realized that heat must be a major factor in the considerations of designing a compact and powerful computer evident by the insulators, sinks and the distribution and air circulation. There were far more mechanical systems than expected in a digital machine and if the CD drive were to disappear, it would eliminate two motors, about four assemblies composed of up to 28 parts and save on space and the use of lithium grease for lubricating the plastic gears and slides, totaling over a hundred pieces. The MacMini was made to be repaired with exception to a few blind rivets used in the hard drive’s axis and the individual components soldered to the PC boards.

The disassembled MacMini quickly laid out.

Further research may include;

• electromagnetic interference EMI that is created by the device / how the MacMini was designed to shield from the EMI of other components such as a wireless keyboard and monitor.

• identifying the manufacturing processes used, including assembly and disassembly.

• creating a resource, use and waste list to understand the life cycle of this product.

• part list : calling out the size, material, manufacturer and function of each part.

• composing a step-by-step guide to disassemble and reassemble this device.

Cheers !

Chris Rand