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820-4652-A iMac 27 not starting.

B

BCN_Techs

Member
Hi,


Got this iMac. First it was damaged power supply, then L7150 was completly burnt. Replace them bot and there were some lines with wrong componentes on it. Replaced and repaird all them and now i am getting LED 1 on. But still not booting machine.



When try to boot pressing button led 1 turns off and turns on again. Checked Power lines for S5-S3 and seems all ok.


I am not getting sys good because of missing PM_SLP_S5_L, Checked SMC and seems to be ok. Anyway reballed it. Still not spinning fans.
 
2informaticos

2informaticos

Administrator
Staff member
Check PCH_DSWVRMEN and all PCH's RTC signals.

Post PM_RSMRST_PCH_L and PM_PWRBTN_L levels.
Trigger SMC_ONOFF_L and check for drop pulse at PM_PWRBTN_L as same moment.
 
B

BCN_Techs

Member
will check it now. Do you know if CPU is dead will it do that with 1st led? Will i get sys power good if CPU is removed?
 
2informaticos

2informaticos

Administrator
Staff member
Is not the first time when I mention about these signals; 4 (four) in total, apart of 32KHz clock.
Look at U1100 RTC block on page 11.
 
2informaticos

2informaticos

Administrator
Staff member
There is separate PCH (U1100) and shouldn't be affected by L7150 overvoltage.
But if CPU (U0500) has been damaged this way, still exists a low "chance" it affected PCH too.

If you do NOT get at least a pulse at PM_SLP_S5_L, or PM_SLP_S4_L when trigger SMC_ONOFF_L, that points to a bad PCH...
 
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