Hello, I am hoping someone can point me in the right direction in fixing the power supply on my mid 2011 21.5" iMac (A1311). The onboard diagnostic LED lights 1 and 2 do not light up when plugged in and powered on. The iMac turns on but does not get passed a black screen. For the past year if turned off the computer would not boot up unless I unplugged the power cord for a few hours. This past week I was updating to 10.13 Sierra and it shut down and will not get passed a black screen now. I pulled the PSU, but everything seems to visually look clean. Attached are some pictures. I really don't feel like buying a new PSU for almost $200 on a computer I do not use very much. If anyone has had an experience in dealing with these PSU's and can pass on any suggestions I would appreciate that. Thanks in advance. -Jay
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iMac A1311 PSU 614-0444
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Re: iMac A1311 PSU 614-0444
I'd look into whether or not it has the equivalent of a 5VSB or 12VSB. If it should but does not, that is where your problem is rather than those output capacitors. If you have no standby voltage, look at small lower voltage electrolytics on the primary side.PeteS in CA
Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
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Re: iMac A1311 PSU 614-0444
"Hi help I need to fix an iMac with the same PS board, damaged by a lightning strike. When I opened it, the board wasn't working at all: I replaced two burned SMD resistors and two capacitors, and the iMac came back to life. But after a short time it became to shut down and restart by itself... I guess I misread the value of some burned component, replacing it with the wrong one(s). Can you please . me? They are R003, R004, C009 and C010. Many thanks in advance!"
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Re: iMac A1311 PSU 614-0444
Same iMac, 21,5" Mid-2011. I'm trying to fix an issue with an on/off flashing backlight, everything else seems to work.
These are the voltages I measured on the PS 14-pins connector:
pins 1, 3, 5, 7, 8, 14: ground
pin 2: +3,3 volts
pin 4: +12 volts
pin 6: nothing
pin 9: +3,3 volts
pin 10, 11, 12, 13: +10,50 volts
Pin 13 is connected to the inverter input, that is marked 12 volts: there's definitely something wrong.
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Re: iMac A1311 PSU 614-0444
Originally posted by jantoman View PostHi. I found out that in my power supply one of two MOSFETs near the output plug was shorted... That's why I couldn't get a correct 12v rail for the inverter. I replaced both MOSFETs and now everything works fine.
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