• Imac 27" A1312 (Main 820-2507-A) No power On

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Imac 27" A1312 (Main 820-2507-A) No power On

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#1 Imac 27" A1312 (Main 820-2507-A) No power On

by robgerr • 11 October 2021, 09:38
Good morning.
I have this imac with the following defect: if I press the power button no sign of life. I have checked the power supply and I am in some 12V output pins. In the connector of the power button I find the 3.3V and drop to 0v when press power button but the machine does not start.Only led001 on but no other after press power button . I tried to do a CMOS reset by removing the backup battery for some time. I tried to reprogram the bios but nothing. I no found traces of oxidation or visually burnt components. The only thing I noticed was that the R5158 resistor was missing and I simply jumpered the two pads as it is a 0hm resistor.
In the L7920 i have 1,11V
C7670 i have 5V

Re: Imac 27" A1312 (Main 820-2507-A) No power On

by Google Adsense [BOT] • 11 October 2021, 09:38

#2 Re: Imac 27" A1312 (Main 820-2507-A) No power On

by ado • 11 October 2021, 13:14
Witam , czy sygnał PM_SLP_S4_L wystawiany przez MCP ma wartość 3,3v po wciśnięciu przycisku zasilania?

#3 Re: Imac 27" A1312 (Main 820-2507-A) No power On

by robgerr • 11 October 2021, 15:48
Hi Ado
Measured PM_SLP_S4_L on the R7053, after press power button voltage up to 3,37V

#4 Re: Imac 27" A1312 (Main 820-2507-A) No power On

by ado • 11 October 2021, 16:04
ALL_SYS_PWRGD ma tez wartość 3,3v?

#5 Re: Imac 27" A1312 (Main 820-2507-A) No power On

by robgerr • 11 October 2021, 16:19
ALL_SYS_PWRGD measured on the R7098 pin 1, 0V
ckecked PP5V_S3_REG and is absent.
Measured U7300, pin 11 12V and after press power button enabler (pin 1 ) voltage up to 3,70V but on the L7320 Coil no voltage.
Checked L7320 resistance to ground 1Kohm

#6 Re: Imac 27" A1312 (Main 820-2507-A) No power On

by ado • 11 October 2021, 18:05
U7300 możesz podstawić? Szukanie PP5V_S3 to właściwa droga bo musi ono się pojawić jako pierwsza linia zasalania S3.

#7 Re: Imac 27" A1312 (Main 820-2507-A) No power On

by robgerr • 1 December 2021, 15:38
Hi ado, replaced U7300 but same problem, no voltage on the L7320 Coil

Re: Imac 27" A1312 (Main 820-2507-A) No power On

by Google Adsense [BOT] • 1 December 2021, 15:38
 This topic is marked as ARCHIVAL. Please only reply if your message contains the solution (Terms and Conditions p. 12.1).
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