This page covers disassembly of the later CRT iMacs. The model used here was a Summer 2001 iMac DV. I've covered this in two parts - access to the motherboard & drives (easy) and further disassembly into the guts of the thing (the PSU, CRT and Analogue Board). I should point out the obvious though - if you just want access to the memory then you can open the trap door underneath without having to undo any screws. You only need to disassemble one of these to change the P-RAM battery, storage drive or a PCB.
Unless you are competent with handling electronic circuitry I really would not recommend gaining access to the main guts as there is a lot of high voltage charge here - enough to throw you across the room and make you utter certain engineering words (or worse).
As usual, a disclaimer:
Unless you're a dab-hand with a screwdriver, don't attempt any of this. Messing around inside your computer could cause damage and in certain cases (such as in the instructions on this page) can be hazardous to your health. This page is just a guide - you follow these instructions at your own risk. You should be careful handling the internals of a computer and follow antistatic precautions or you may cause damage.
Let's start with the easy stuff.....
Motherboard, Storage Drives and Down Converter access
1. Place the iMac onto it's screen. You may want to lay down a cloth first to avoid scratching the screen. Use a flat blade screwdriver to prise off the underside grill as below...
2. Remove the arrowed screws
3. Remove the arrowed screws
4. Carefully pull away the lower clam shell of the case. Before you do though, bear in mind the following comment (thanks to Vincent Cawley for sending me this)....
I found your illustrated imac disassembly page very helpful. I do have one suggestion. For step 4, I suggest it's important to rotate -- not pull -- off the lower half of the clamshell. I destroyed my headphone adapter board by tugging off the case. Strangely, if that board is destroyed or absent, the computer thinks there are headphones plugged in and refuses to put sound out through the internal speakers.
I can understand the speakers not working with the board damaged or removed - the 3.5mm headphone jack connector effectively has an in-built switch which breaks the audio connection to the speakers when headphones are plugged in. A damaged or removed board could look like a broken connection to the iMac making it think headphones had been plugged in therefore shutting off the speakers.
5. Remove the six screws holding the shielding in place
6. The exposed motherboard. The labelled areas are... A: P-RAM Battery, B: Memory DIMMS (x2 on this example), C: Storage Drives, D: Down Converter PCB. To remove the storage drives just undo the relevant screws and connecting cables. The same goes for the motherboard and down-converter PCBs.
Access to the CRT and PCB/Analogue Board
7. Only continue the disassembly process if you really have to. If you are not electrically qualified and have no reason for accessing the PSU, CRT or Analogue Board then do not continue. High voltage charges are present in the following section of the iMac. For those who simply have to continue, remove the five screws on the upper case clam...
8. Use a small flat blade screwdriver to pop off the two screw covers from under the screen surround and undo the screws behind them. Use a larger flat blade screwdriver to pop the screen surround from the coloured rear clam half.
9. Pop off the two screw covers from the top of the case and remove the screws from behind them. The picture below shows a small screwdriver popping off the right cover...
10. Push down carefully on the sides of the coloured rear clam to release the clips. It may then be pulled away from the rest of the unit.
11. The internals of the unit with the CRT at the top of the picture...
12. With power removed the CRT should discharge through a resistor but it's best to check this is the case before sticking your fingers too close. Connect a crocodile clip to each end of a cable and clip one end onto the shielding around the CRT. Clip the other end to a metal flat-blade screwdriver with an insulated handle and push it gently under the rubber cab connecting the anode wire to the CRT. Make sure the screwdriver makes contact with the metal connector under the cap to discharge any electricity in the CRT. Leave it connected for several seconds. You may see a spark or hear a crack.
13. Lift up the rubber cap and use the screwdriver to carefully ease out the anode.
14. Undo the clip at the rear of the unit holding the two case sides together.
15. Remove the screw from each side of the front of the unit above the speaker ball (ignore the crack on my guinea pig model below ! )
16. Remove the screw from each side of the rear-front of the unit (if that makes sense)...
17. Remove the two screws from the underside of the unit on either side of the external monitor port.
18. Remove the screw from either side of the rear of the CRT - you may need to move the microphone and screen wires out of the way first...
19. Remove the side panels.
20. Remove the large grey connectors that connect to the main PCB on the back of the CRT.
21. Undo the screws on the signal connector and unplug it.
22. Undo the spring clip retention screw around the neck of the CRT and remove the spring clip.
23. Gently pull the PCB from the back of the CRT. Don't twist it or you risk breaking the neck of the CRT - the PCB is just pushed on with connecting pins and firm but gentle pulling will eventually release it.
24. The CRT can now be gently lifted and pushed forward allowing access to the screws and two plastic clips holding down the PSU/Analogue PCB.
25. Remove the connectors to the PSU/Analogue PCB and it can then be removed. Beware of charges stored in the capacitors on this board. Don't touch unless you really have to.
If you're going to the effort of removing this board then I'm guessing you have a problem such as a flyback transformer failure. This is a common fault on the CRT iMacs and is a result of this component overheating due to lack of ventilation. The symptoms may include the following:
iMac powers up briefly with no display before shutting off;
iMac powers up normally but with no display (although external video connector works);
iMac won't power up properly at all.
My own iMac suffered a problem in May 2004. I switched it on and it made a nasty crackling-popping noise. The display was also very jumpy. I took it apart and the problem was immediately obvious - capacitor C905 had failed. I say it was obvious, the top of the capacitor was deformed to how it used to be (I had a good look over that board when I wrote the above disassembly instructions). Previously this radial electrolytic capacitor had a flat top (as they do), but now there was a bulge on one side. Fortunately I had a replacement in stock and after fitting it, all was fine again.
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