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iMac A1418 - 820-3302 - Turn on when I remove BR2032 always need to remove it...

S

samstown

Member
Hello,



Customer said iMac stopped booting. She's not using it a lot. Last week, she wanted to turn it on... no sign of life. She went to Apple, they said it's dead...need to buy a new one.

I remove the screen, I can see led 1 on. I tried to bypass power button, doesn't help, SMC reset, doesn't help.I unplugged all cables from motherboard except the power, I took card out, I remove the BR2032, plug power... it starts.


I did some test without BR2032 and screen, everytime I plug power cord, it's start.

I've measuer BR2032, it's not perfect but still green. I remove it and user another one. I plug everything back. iMac starts (FAN full speed always), I login, setup wifi... and then I shut it down properly. After shutdown, iMac doesnt start. I always need to remove the BR2032 to make it working again, not very convinent.

Last I tried yesterday night, I tried with a CR2023 (just to try), it starts, (FAn were not always on) I tought it was ok... but no.. same. I shut it down and then it doesn't start again.


I've tried to disconnect Camera as mentionned in other post, it doesn't help. I've tried to unplug cable after cable and try to power it each time, doesn't work. It only start when I remove the BR2032. If I don't place a BR2032, same behavior, it starts but won't boot again If I shut down properly. If I remove power cord when login screen is displayed, it will start... It doesn't like proper shut down...


Basically, with not BR2032 installed, if I shut down iMac properly ( from login screen, I don't need to login to test this behavior) it doesn't turn on after. I need to unplug power cord and then it will start again.



Thanks

Sam
 
S

samstown

Member
With BR2032 - Doesn't boot, even if I remove power cords.
Without BR2023 - It boot but need to remove power cords for 15 secondes after proper shutdown.
Fans always full speed on.
 
S

samstown

Member
SMC_ASSERT_RTCRST = 0V
PPVBATT_G3_RTC_R = 3,07V
PPVBATT_G3_RTC = 3.08V
RTC_RESET_L = 3,28V
C2210 PPVOUT_G3_PCH_DCPRTC = 1.55V
PCH_CLK32K_RTCX2_R = 0.25V
PCH_CLK32K_RTCX1 = 0.35V
 
Last edited:
2informaticos

2informaticos

Administrator
Staff member
" 3.29V on PCH_SRTCRST_L
.......................
RTC_RESET_L = 3,28V"
Still missing two.
Take a better look at page 18.
I mentioned to check DC signals, not clock.
 
2informaticos

2informaticos

Administrator
Staff member
OK, then the 4 signals look good.
You've just posted the last two; aren't go to same RTC block of PCH?
We mentioned so many times these signals on the forum.
I can't believe you didn't note them yet.

Check PM_DSW_PWRGD, PCH_DSWVRMEN, PM_RSMRST_PCH_L, PM_PWRBTN_L.
 
S

samstown

Member
Ok, Ill save those in my do to list.
PM_DSW_PWRGD = 3.42V
PCH_DSWVRMEN = 3.17V
PM_RSMRST_PCH_L = 3.31V
PM_PWRBTN_L = 3.41V
 
S

samstown

Member
Using tweezer, I connect C600 ( SMC_ONOFF_L ) to GND and I monitor PM_PWRBTN_L with Multimeter, it's stays at 3.41 V
 
2informaticos

2informaticos

Administrator
Staff member
You must make a temporary contact only, like simulating power button action.

HOW TO collection

I hope this "How to" collection will help our members. I will possibly modify this post in time, if updates available. Trigger SMC_ONOFF_L (PMU_ONOFF_L): It reffers to simulate power button function, when the keyboard is not connected. We need to do this when we work with the board...
boards.rossmanngroup.com boards.rossmanngroup.com
 
S

samstown

Member
Thank you. I did read the post before but I didn't solder wire, maybe I should have started with that instead of tweezer. Now I've solder a wire, when I connect to GND quickly, PM_PWRBTN_L drop to 0.3 and iMac boot. I've placed B2032 back. iMac is working correctly. Thank you for your help.
 
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