iMac No Diagnostic leds lite

Question

iMac Intel 21.5" EMC 2805

Model A1418 / Mid 2014 / 1.4, 2.7 & 2.9 GHz Core i5 or 3.1 GHz Core i7 Processor

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Jack Graham @jackgraham22062

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发帖于: 2017年12月8日

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iMac No Diagnostic leds lite

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

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Jack Graham @jackgraham22062

声誉积分: 91

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发帖于: 2017年12月21日

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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

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