Model A1311 / Mid 2010 / 3.06 & 3.2 GHz Core i3 or 3.6 GHz Core i5 Processor

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iMac non-responsive... Bad PSU?

Hi,

Im working on a Mid 2010 iMac EMC 2389 that appears to have no power at all. The power button does nothing, and I have tried different outlets and power cables. My thoughts are the PSU.

Below is a picture of the PSU with some of the pins outlined to show what I am talking about.

I tested that I was getting 120V AC at the two leads on the board (in blue) and I was. I read online that the lead outlined in grey was ground (it would be the bottom left pin if you are looking at the connector with the latch on the top) and the red pins should be the various power rails. I tested with a multimeter and found that there was no voltage across any of the pins to ground with the AC connected. So does this mean bad power supply?

I also read that there are leds to the right of the ram slots (if you are looking at the system as if you were using it), however I see nothing when plugged in and pressing the power button, so I guess that means no power to the mainboard, right?

Is there a way I can try to jump the PSU or anything, I know in a ATX power supply you do green to ground but these are all black and not labeled. But because there was no power output on the pins, I assume its just bad. What are your thoughts? Thanks!

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Picture: https://imgur.com/a/4NNJHf2

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Diagnostic LEDs

There are four built-in diagnostic LEDs on the logic board that can help troubleshoot the computer. LEDs are located on the front center of the logic board, above the IR board, to the left of the SMC reset button.

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LED Functions

LED #1

• Indicates that the trickle voltage from power supply has been detected by main logic board.

This LED will turn ON when you connect the iMac to a working AC power source. The LED will remain ON as long as the computer is ON or asleep.

• When computer has been correctly shutdown, the LED#1 behavior may differ:

• - If a startup event is scheduled in System Preferences/Energy saver, LED#1 will stay ON after a correct shutdown,

• - If no startup event is scheduled in System Preferences/Energy saver, LED#1 will turn OFF and will stay OFF as long as AC cable is kept connected and AC power source is present.

Disconnecting the AC cable and plugging it back will turn back this LED ON , even if computer is still off.

• After disconnecting and reconnecting the AC power source, this LED could remain OFF if the AC power source is missing or disconnected , if the logic board is disconnected from the power supply or from the AC receptacle, or if the power supply board is faulty.

LED #2

• Indicates that computer is turned on. This LED will be ON as long as computer is turned on (but is not asleep) and power supply and voltage regulators are working correctly.

LED #3

• Indicates that computer and video card are communicating. This LED will be ON when computer is communicating properly with video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the backup battery (on back of logic board) may need to be reseated, or the video card might be installed incorrectly or needs replacement.

LED #4

• Indicates that computer and LCD panel are communicating. This LED will be ON when computer is turned on and video signal is being generated. If LED#4 is ON and there is no image on display, then the LCD panel, the LED backlight board, or the cables between LCD and logic board or backlight board might be installed incorrectly, or need replacement.

LED Startup Sequence

LED #1 = Power available.

If no LED is visible:

• First disconnect the AC cable from computer, then reconnect it to reset the LED status, in case computer was correctly shutdown and AC was kept connected since

• Verify AC source

• Verify known-good AC cable is connected

• Verify cable connection between AC inlet and power supply

• Verify cable connection between power supply and logic board

• Verify power supply

LED #1 + LED #2 = Power available, and system is powered on.

If second LED is not visible when power button is pressed:

• Verify power button connection to logic board

• Verify power button functionality

• Verify cable connection between power supply and logic board

• Verify power supply

• Verify logic board

LED #1 + LED #2 + LED #3 = Power available, system is powered on, and video card found.

If third LED is not visible after power on:

• Verify that the MXM video card is seated properly

• Verify if boot chime is present and fans are running when powered ON (reset SMC and

PRAM, reseat or check backup battery if necessary for proper boot up):

If POST boot chime is not heard, go to Won’t Start Up symptom flow,

If POST boot chime is heard, go to No Video symptom flow.

LED #1 + LED #2 + LED #3 + LED #4 = Power available, system is powered on, video card found, and internal LCD found.

If fourth LED is not visible after power on:

• Verify internal DisplayPort cable connections between LCD panel and logic board

• Inspect LCD display cables for cable damage

• Verify external video functionality, and according to result check the following items:

If external display works then verify/replace the LED backlight board

If external display works then verify/replace the LCD panel

If external display does not work verify/replace the logic board

Logic Board Test Points

Test points, which can be used to verify proper power flow, are accessible in center of logic board, to right of SMC Reset button, when LCD panel is removed. All voltages given in Troubleshooting Symptom Charts assume that computer is plugged into a known-good power outlet with a known-good AC cable. Some guidelines for using test points:

• Warning: HIGH VOLTAGE: Use extreme caution when live testing!

• Do NOT lean over or touch the power supply area during live testing.

• Keep your fingers behind finger guards on test probes when measuring.

• Turn dial of voltmeter/multimeter to measure DC (direct current, usually indicated by a solid horizontal line over dashes). If your voltmeter requires a set voltage range, choose a DC range that includes the voltage you are measuring.

• Connect black probe to ground. Connect red probe to test point and verify voltage.

Test Point Function

Pin 1

Ground

Pin 3

5V power for Hard Drive(s). Note: If present, the 12V power will come directly from the Power Supply to the Hard Drive thru the power harness cable.

Pin 4

Standby 12V power (permanent power coming from power supply, present as long as AC cable is connected, even if computer is off); corresponds to LED #1

Pin 6

Backlight Control pulse width modulated signal (from logic board to LED backlight board, to adjust the backlight level setting according to user setup)

Pin 11

12V Run-Mode power to logic board (coming from power supply, present as long as system is on or asleep); corresponds to LED #2

Pin12

Power On Request signal (from logic board to power supply when power button is pressed)

Pin 13

Backlight Enable (signal from logic board to Backlight Controller board, to enable backlight

Startup and Power

No Power, Dead Unit

Check Result Action Code

1. Power ON system. Verify if there is any indication that the system has powered up (fan rotation, hard drive or optical drive noise, backlight turns on).

Yes

The symptom is powering up.

Go to Won’t Start Up.

No

Go to step 2.

2. Disconnect AC cable Remove glass and LCD panel and locate the diagnostic LEDs in the middle of logic board.

Reconnect AC cable to system. Verify if diagnostic LED #1 turns ON. You may alternately check for presence of a 12V DC signal between pin 4 and pin 1 of the logic board.

Yes

Standby power voltage being supplied by power supply.

Go to step 3.

No

Go to step 4.

3. Press power button while monitoring diagnostic LEDs. Verify if LED #2 turns ON and remains ON after releasing

the power button. You may alternately check for a power request signal between pin 12 and pin 1 of logic board.

Yes

Power supply functioning and logic board detects supply voltages and is powered on.

Go to Won’t Start Up.

No

Go to step 5.

4. Disconnect AC cable. Carefully inspect the connectors between AC inlet and power supply, then DC connectors and cables between power supply and logic board, for damage or poor connections.

Yes

Reseat misconnected cable(s), or replace damaged one(s).

No

Replace DC power cable harness. Go to step 8.

5. Inspect power button and verify if it is properly connected to the logic board.

Yes

Go to step 6.

No

Reconnect power button.

6. Disconnect power button from logic board. Inspect cable and connector for damage. Using a multimeter (set as ohmmeter), verify continuity between the two pins of the power button when it is pressed.

Yes

Power button is functioning correctly. Reconnect power button to logic board and go to step 7.

No

Power button faulty. Replace rear housing (which includes power button).

7. Reconnect AC cable Press power button and Verify if system turns ON. You may alternately check for presence of a 12V DC signal between pin 11 and pin 1 of logic board when power button is pressed.

Yes

Power supply functioning. If system still won’t boot, go to Won’t Start Up.

No

Replace DC power cable harness. Go to step 8.

8. Press power button and verify if system turns ON.

Yes

Issue solved with replaced DC power cable harness.

No

Replace power supply.

Go to step 9.

9. Press power button and verify if system turns ON.

Yes

Issue solved with replaced power supply.

No

Reinstall power supply and replace logic board.

So in your case it looks like a bad power supply and no there is no reset or jumper like you are used to.

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So I am getting no leds and no power anywhere except the mains 120v ac on the power supply. So it is definitely the psu. Hopefully nothing else was damaged when whatever happened broke the psu.

I keep seeing things about the SMC reset button, and see it printed on the mainboard, but dont see an actual button. Are there pins that are to be jumped to reset it, as I might have to do it later on when I replace the PSU.

Thanks for your response, very helpful

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Hi, my Home Mid 2010 iMac from what I’ve read so far, is giving me a strange situation. I was using a 1TB WD hard drive to boot from (internal HDD died), and since 2 weeks ago it worked perfectly. Now it won’t boot up. Progress bar and apple logo appear but it will stay there forever. Sometimes progress bar advances 100% and sometimes just a bit. I blamed the bad HDD so I removed it from iMac, but problem prevails. But if I used the same USB ports with a DVD drive it would boot from Snow Leopard DVD OS disk and let me do a fresh install of Snow Leopard booting up as many times as I wanted. But if I upgraded to El Capitan (only OS available at app store) then problem would come back.

I then went ahead and prepared (at works other good iMac) 3 HDD’s with a fresh High Sierra OS: a 100Gb 2.5 Sata, a 1TB 3.5 Sata and a 120Gb 3.5 IDE. All disks verified, repaired, tested, good and booted from on work’s iMac.

Last night I placed the 1TB as an internal HDD and problem prevails. I even ran Command S and booted up in Terminal and run FSCK -Fy which found no internal disk errors, all seemed to be OK. Im leaning now to a possible problem on logic board, but from what I read mine does not have the tell tale signs of a bad logic board: mine chimes, boots from command-S, -V, option(choosing any other disk/device connected) long beep if there is no RAM, and has visual display (apple logo and Snow leopard running good), so Im really at the end of my wits.

What could be possibly wrong?

Cheers!

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