Chosen Solution
Hey Have an imac i picked up on ebay for a fix up like i did with the imac im typing on right now i digress anyway when i plug the power cord into a good AC source the NO. 1 led blinks then turns off. When i push the power button nothing happens no fan spin. Things ive checked power button has continuity when pressed: Good AC jack where the power cord plugs in then connects to psu has continuity: Good Here is my diagnosis: PSU BAD/FAUlTY What do you Guys think ive ordered a good working psu if this does not fix it i have a schematic and boardview ready to go i know how to read schematics as i have fixed tube radios in the past So i know what im doing…. If no one replys and the psu does the trick like i think it will i will report back as to help future servicemen/women
Update: got the mac working Got the psu in with no change so i pulled up the schematic and probed the output of the psu 12v still no led no 1 so i found the led on the schematic and it said 3.3v on positive side of led (3.3 is the trickle voltage from second smaller connector on psu) probed led no 3.3v (i noticed that the led would flicker sometimes so i thought loose connection at a solder joint) when i applied pressure to led it would flicker more often) so i reflowed the led area and the MAC TURNED ON i remeasured the led and got 1.2 v when its supposed to be 3.3v checked a cap right next to it and got 3.3v on one side and 1.2 on the side going to the led so i think the heat reformed the cap and fixed a bad solder joint FYI IM WRITING THIS ON THE MAC IN QUESTION
That’s the correct first step, the PSU. Logic boards seldom fail.
