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Hello, recently a school gave me an imac g4 that was used for educational purpose and the school said that the mac was dead. So i first pluuged the power outlet and it booted but with a weird screen changing to completely white. A few weeks ago and yesterday, i just replugged it to test the mac but now, the mac won’t boot up, no fan nothing. Only a fast clicking sound coming from the power supply that stops sometimes after a few seconds. I dissasembled all the imac and look for any damage on the mac. With a multimeter i checked the voltage coming from the first power supply board and i got 400 v continue but on the second board, i have no voltage. Have you got any tips to look for maybe shorted parts or capacitors that usually break up in these machines ? Thanks for help
G’Day Correia ; You are on the right track , HOWEVER , to be really successful one should purchase a decent ESR meter to check any electrolytic caps in the power supplies . An ESR tool (Effective Series Resistance , I could be wrong , been a long time for that definition ) will test capacitors ‘in circuit’ . No need to de-solder . HOWEVER there can be a gang of caps in parallel and some meters will give a pass . If any have swollen tops or stuff leaking they are bad FOR sure . If any are in a parallel gang I would swap them all . Hope you have a heavy duty motorized solder sucker to get caps out of multi layer boards ( heat from most hand irons will get pulled away into large copper ground planes ) Sorry I have not had any G4 experience , but Apple makes such good quality I doubt caps are bad , but , I have done so many other devices and brands that I would not be surprised . That ‘clicking’ you mention could now be a shorted MOSFET causing switching power supply to constant reboot . Use DVM on semiconductor junction test to look for bad power MOSFET or transistors . Less likely is you are hearing the hard drive smacking the heads against the frame . Shed the hard disk for boot test maybe . Just some thoughts , Good luck Hugh
