iMaCC Upgrade

Brad R. Sturges has completed the CC-to-iMac upgrade and has kindly agreed to share step-by-step instructions for performing this upgrade. Please direct specific questions about the upgrade to Chris Lawson. They will be forwarded to Brad, allowing this document to be kept up-to-date, accurate, and as detailed as possible.

Parts and Equipment List

  1. Color Classic
  2. crimp-on connector close-upLogic board and processor from any tray-loading iMac
  3. 1U rack-mount ATX power supply capable of delivering at least 180 watts
  4. 2" processor fan (for cooling the iMac's CPU)
  5. Several crimp-on male and female connectors (10 pairs should be sufficient; see photos at right and below)
  6. 2.5" IDE hard drive
  7. 2.5"-to-3.5" IDE adapter board
  8. IDE ribbon cable, at least 9" long
  9. Dremel or other rotary tool
  10. Quality soldering iron
Notes on parts and equipment:

Performing the Upgrade

Tampering with a CRT can be dangerous. You should only perform this modification if you are comfortable with electronics and understand the safety precautions that should be taken when dealing with a CRT.

  1. Perform the VGA upgrade on the CC. You only need to perform the first two steps of the VGA upgrade.. The iMac ignores the sense lines entirely and assumes the monitor hooked up to it is VGA.

  2. AC power tap close-upNow, solder on the three wires that will power your new PSU. Locate the three pins on the underside of the analogue board that are supplied with AC power when the switch is on. Be sure to use wire capable of handling the current; 14-gauge wire should suffice. Crimp a quick connector on the end of each wire for easy disassembly in the future.

  3. Fan connector close-upThe final analogue board modification is to supply power to the fan connectors located near the power switch. The original wiring will not power the fan unless the analogue board "knows" the computer is on. This modification neuters the analogue board's ability to "know" whether or not the computer is running. Isolate these connectors using the same technique as you used for the VGA modification. Once isolated, solder two wires to them with connectors crimped on the ends. You'll eventually use these to attach 12v lines from the new power supply.

  4. You must now clear out the chassis to make room for all of the new components. First, remove the slots on the chassis that the hard drive sled slides into. The power supply will only fit under the analogue board if these tracks are gone, as it must lay flat on the very bottom of the chassis "shelf." This can be done easily with a rotary tool.

  5. Chassis modification close-upThe underside of the chassis (where the original motherboard resided) must be cleared out as well. Remove the material in this area to make sure you have as much room as possible. Again, a rotary tool makes this very easy, though a good portion of this can be achieved with a small hacksaw too.

  6. Motherboard supports close-upNow you need to develop a support structure for the iMac motherboard. Cut slots in the side of the chassis and place supports in these slots. (You can see one of them in the photo above, and again in the photo at right.) Metal strips are cheap and easy to find, but be sure to insulate them with plenty of electrical tape. Wood or plastic can be used too — you just need something that can support the weight of the motherboard. One piece should an L-shaped bracket, which is used to create a stop in the front of the chassis so the motherboard could not be pushed too far into the chassis. Make sure you place this piece such that the ports are flush with back of the CC when the board is fully inserted.

  7. Now we can move on to connecting up the power supply. With a wire cutter, remove the 20-pin connector of the power supply as close to the connector as possible. You want these wires to be able to reach down to the motherboard from the HD bay, since they will be used to power the motherboard. Most 1U power supplies fit without modification, but the Achme flex-ATX power supply requires that the outer metal casing be removed first. If you choose this PSU option, you must make sure the holes that mount the PSU circuit board to the casing are properly grounded.

  8. In the iMac, the motherboard plugs into a power filter that sits directly below the motherboard. While this unit is not needed, its connector greatly simplifies the connection of wires to the bottom of the motherboard. Otherwise, you must solder directly onto the motherboard and will have no way of easily connecting and disconecting the power. To use the connector, simply cut off the power filter connector with a rotary tool, place it on a small piece of blank PCB, and solder the wires onto the back of the connector.

  9. Now you're ready to wire up the motherboard itself. You'll need to consult the iMac Rev A-D Pinouts for the correct pinouts. (The pin numbering assumes the orientation of the board is with the processor cage facing the ground, and all the ports facing right.) The number of wires needed does not precisely match up to the number of wires you have on the power supply, but it won't matter as long as you double up where necessary. For example, if the motherboard needs a red wire on a pair of pins on the same vertical row, simply solder one wire to both of them. The only issue is that the iMac motherboard requires two +12V (yellow) wires and the PSU only has one in its main connector. Just use a yellow wire from one of the spare hard drive connectors instead.

  10. Once you've made the connections to the motherboard, you can now make the rest of the connections you need. You will need to plug a hard drive power connector into your 2.5" IDE hard drive's adapter board. Where you mount the hard disk is really up to you, as its small size allows a nearly limitless array of mounting options. Secure it to a rigid surface if you plan to transport the computer anywhere.

  11. Crimp a quick-connect terminal onto one yellow wire from the PSU and do the same for a black wire. Then, connect these two wires to the power wires you soldered on for the fan contacts. While you're at it, connect the wires from the analogue board's power input to the new PSU. Be sure to match the hot, neutral, and ground wires properly.

  12. Now you can move on on to the video connections. Remember, you should have performed the first two steps of the VGA hack already. The connections to be made between the CC's analogue board connector and the iMac's video connector are as follows, with all pin numbers referring to either the Takky Connector Correlation Tables (CC analogue board) or iMac Rev A-D Pinouts (iMac board). Colours have been matched to the iMac Rev A-D Pinouts for consistency.

    iMac Video Connector Pin (function)CC Analogue Board Pin
    1 (R ground)14
    2 (R signal)15
    3 (B ground)10
    4 (B signal)11
    5 (G ground)12
    6 (G signal)13
    8 (horizontal sync)9
    10 (vertical sync)
    9 (sync ground)8
    11 (contrast control)19
    15 (contrast control ground)18
Notes on performing the upgrade:

Last modified on 10 February 2004
by Chris Lawson
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