820-2494 Only first LED

[No-Clean]

Clean board just died suddenly.

First LED comes on with 12V are injected to PP12V_S5
When power button is shorted nothing happens and SMC_ONOFF_L stays at 3.3V
No shorts found.

PP1V1_S5_REG - 1.1V
PP3V3_S5_REG - 3.3V
PP5V_S5_LDO - 5V
PP12V_S5 - 12.05V

Missing 5VREG_EN and PM_SLP_S4_L

Im not very good with this old iMacs, any guidance will be greatly appreciated.

 

[2informaticos]

Use S5010 pads for test, instead of power button.
If starts, then bad power button, connector, or cable.
Be sure R5010 is good.

 

[No-Clean]

R5010 is good 1k
Diode mode on S5010:1/2 is same as J5010:1 so the connection is good
I am not using power button for testing, I am shorting J5010:1 to ground

 

[2informaticos]

Then SMC_ONOFF_L MUST drop to 0V, when trigger S5010.

 

[No-Clean]

Ok now it does, sorry for the hold up, it does drop to 0.300V when I short J5010:1 to ground, but only fist LED remains lid.

 

[2informaticos]

Check for drop pulse at PM_PWRBTN_L at same time.
If present, check for pulse at Pin 1 of U7300; this chip fails a lot.

Do you get correct voltage at L7920?

 

[No-Clean]

L7920 1.1V both ends

When I short J5010:1 to ground I get 3.3V on U7300:1 but U7300:12 still 0V even thou this chip was making that voltage on the donor board.

 

[No-Clean]

I put the chip back on the donor board and now it is dead, looks like the temperature when removing it is killing it or then I install it on the other board that board is killing it, Im a little confused here...

 

[2informaticos]

Check Q7330, D7301, R7324 and C7326.
Diode mode to ground at L7320?