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Old 10-16-2021, 05:51 PM   #1
whirlpool
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Exclamation Imac model 2017 is complely dead No light-12v is ok-ps is changed

Hello everyone

IMac model 2017 intel i5 Completely died after updating the operating system , no lights are on the board. I changed the power supply before just to gain experience, but again the problem has not been solved .. I have done a lot of research about it ...
I checked the SMC U5000 and pp3v3 pp5v. If you look at the schematic, the first light is called le0301 with the abbreviation in pp3v3 S5 circuit. before this I get 12 volts, 5 volts and 3 volts in U7600 well. but after U7600 and before reaching LED1_S5 everything is cut off . I reflowed the u5000 with a temperature of 405 degrees and I do not think the problem is with the SMC.
first i need voltage in to LE0301 .i dont know how can i do that?
Please help me.Thank you very much
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Old 10-16-2021, 06:25 PM   #2
mon2
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Default Re: Imac model 2017 is complely dead No light-12v is ok-ps is changed

What is the logic board number for your box? It should 820-xxxx format.

Also can you link the schematics if they are posted on this forum? If not posted, can you post them in the schematics section?
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Old 10-20-2021, 12:13 PM   #3
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Default Re: Imac model 2017 is complely dead No light-12v is ok-ps is changed

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Originally Posted by mon2 View Post
What is the logic board number for your box? It should 820-xxxx format.

Also can you link the schematics if they are posted on this forum? If not posted, can you post them in the schematics section?
hi thanks for reply
i use schematic for pcb 820-00597 imac 2017 intel i5 8g ram 4k
Attached Files
File Type: rar A1418 - 820-00597.rar (6.67 MB, 15 views)
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Old 10-20-2021, 03:02 PM   #4
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Default Re: Imac model 2017 is complely dead No light-12v is ok-ps is changed

Basic troubleshooting is essential! Try the simple stuff first, like CMOS battery, physical inspection, disconnecting non-essential connectors, measuring resistance/voltage of rails. Reflowing a SMC is usually the last resort, not the first. You can introduce faults into a device by doing random stuff like that.

My experience thus far with iMacs is usually a very minor fault, like a shorted cap from corrosion can cause a dead board. So physical inspection under a microscope before you do anything is essential. Examine closely the areas under where the bottom of the LCD is, as chemical cleaners used to clean the screen often seep in through there. I've had shorted caps on the back of the board (facing the LCD), and on the headphone jack cause dead systems.

Also check for dislodged or moved components under the microscope. As the iMac motherboard sits upright at an angle, it's easy to drop a tool on it while removing the screws for it. I've had a sensor issue (fan run at full speed) caused by a resistor knocked off by a dropped tool for example.

For that first LED to light up, you need to check that all S5 voltages are present (pg 116) and power good signals for each are valid. Do the simple stuff first and work your way up.

Last edited by reformatt; 10-20-2021 at 03:04 PM..
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Old 10-25-2021, 03:40 AM   #5
whirlpool
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Default Re: Imac model 2017 is complely dead No light-12v is ok-ps is changed

Quote:
Originally Posted by reformatt View Post
Basic troubleshooting is essential! Try the simple stuff first, like CMOS battery, physical inspection, disconnecting non-essential connectors, measuring resistance/voltage of rails. Reflowing a SMC is usually the last resort, not the first. You can introduce faults into a device by doing random stuff like that.

My experience thus far with iMacs is usually a very minor fault, like a shorted cap from corrosion can cause a dead board. So physical inspection under a microscope before you do anything is essential. Examine closely the areas under where the bottom of the LCD is, as chemical cleaners used to clean the screen often seep in through there. I've had shorted caps on the back of the board (facing the LCD), and on the headphone jack cause dead systems.

Also check for dislodged or moved components under the microscope. As the iMac motherboard sits upright at an angle, it's easy to drop a tool on it while removing the screws for it. I've had a sensor issue (fan run at full speed) caused by a resistor knocked off by a dropped tool for example.

For that first LED to light up, you need to check that all S5 voltages are present (pg 116) and power good signals for each are valid. Do the simple stuff first and work your way up.

Thank you very much for your answer. I did some basic checks before opening the motherboard, such as checking the battery or USB socket and other connections. And any chemicals, etc. have been checked on the board. Unfortunately, my schematic is only 87 pages and I do not know what you are using. Please upload that schematic for me here ... I am also a schematic of iMac. I uploaded myself in the previous post .... Thanks anyway
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Old 10-25-2021, 08:18 PM   #6
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Default Re: Imac model 2017 is complely dead No light-12v is ok-ps is changed

Refer to pg 116 and check the G3H and S5 rails first. Since you have no LED's lit, this means that either the PP3V3_S5 or the S5_PWRGD is missing. If you have 12V to the board, but no G3H rails, this is where your troubleshooting should start.
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