You can't boot without RAM, the iMac will beep to tell you there is a RAM problem. Maybe you switched the iMac on without RAM. In that case it should beep. When there's only a problem with a sensor or a fan, you should run apple hardware test (original snow leopard DVD, or leopard 10.5.x CD) which will tell you which sensor or fan is defective.
Hi, if you are sure it's the door switch (mostly there is more than one however) why don't you take it out and go to a parts shop for a new one. When you are skilled you may open the switch and clean the bunrt contacts. Also look for fuses blown (sometimes there's one in the HT leads to the microwave Xmitter too).
Hi, When none of the LED's are lit, this means there is no power at all, and one would suspect the power supply. Don't jump to conclusions too fast, however, and check the AC input connector, mains filter and AC wiring to the PS board. If you know how to handle a multimeter, check the mains voltage on the PS board. You can also unplug the connector to the logic board, and see if you have the tricle (stand-by) voltage (about 2,5 V DC). Be aware that a power supply has protective circuits on the main output voltage line (12VDC). When there is a short circuit in the logic board (or audio board, video card etc), you won't be able to start the computer (LEDS 2/3 remain dark) but you can have the trickle voltage. I was fooled once by this situation, thinking of 'only' a defective PS, but when I pulled out the video card my iMac came back to life ! I don't know if the trickle voltage line is protected (guess not).
I've had two 2133 20' iMac's and both had a removable CPU. I replaced the 2,0 Ghz processor of one of them by a 2,4Ghz (coming from a 24" defective logic board) and it runs perfectly well. It shows up in the system info part as a 2,4 Ghz Intel Core 2 Duo. So have a look under the bonnet to see if it's removable !
Hi, I don't see why you can't skip these steps. After removing the TFT panel you should have easy access to the power PCB. I exchanged a HDD on a similar unit, and did not need to remove the logic board or speakers.
Hi Alfonso, First check out if it's an inverter/backlight problem or it's a group of pixels behaving badly. Look at the display (put on a white or lightgray screen) from a very short distance. When you definitely see some groups of pixels flickering (and others remain stable), this means the pixels are blinking. This could be caused by the display itself, or the video card. When an external DVI monitor has the same problem, it's definitely the video card (unlikely though, because the video card has 2 separate video outputs). An old cracked or scratched TFT panel can come in handy to use as a test display (also to test the backlight). When it's more like a horizontal region on the screen that is flickering, the problem comes from the inverter or one of the four horizontal tube lights. The inverter has four output stages, each driving a lamp. Exchange 2 lamp connectors to see if the flickering region moves. When it does : exchange inverter (or try to repair it : maybe the cores of the step-up transformers...
After changing the display can you see it is working when lit with a flashlight ? Yes : the backlight still isn't working. What do you know about the exchanged parts ? Brand new or used ? Even new parts can not always be trusted to be all right. So it still could be the inverter, or the lamps in the display panel. When these parts are brand new and tested, check the inverter supply (mostly 12VDC) voltage. Maybe there is a fuse on the power supply which has blown. Also check the low voltage wiring to the inverter. There can be a short circuit in the high voltage wires to the backlight lamps, causing the fuse on the new inverter to blow instantly. SMD fuses can be recognized by the desription on the PCB (F1 e.g.), and can easily be tested with a multimeter, and replaced by a glass fuse by soldering wores to it. Then there is the baklight control voltage (mostly a PWM signal) coming from the motherboard to the inverter (sometimes passes the power supply PCB). It controls the brightness of the backlight and...