iMac 5K 27" 820-00134 - Dead board due to USB?

[Jay Khan]

Hi Friends,

I have an iMac, which customer says made a boom sound, and never turned on; board show no diagnostics lights. I inspected the board and it seems the 3rd USB port from left (looking at the back), had some issue, resulting in burn out of:

1. L4702 (dual filter) that carries the P and N channels of the USB.
2. L4701 - likely delivers PP5V_S4 to the USB.
3. U7700

Now, I am not sure if this could have caused the PCH to die as L4702 connects the USB to PCH. U7600 is not generating PP3V_S4 or PP5V_S5. PM_EN_REG_P5V_S4_R has 0.4v.



I removed U7700 to see if it may help; but still no diagnostic lights. Any ideas?

Thank you!

 

[ThienBui]

it is very difficult to judge and need a direct test

 

[Jay Khan]

it is very difficult to judge and need a direct test

What do you mean by direct test? Can you please provide any guidance? I am really surprised that the USB port can cause such big problem to such an expensive machine.

 

[ThienBui]

all electrical circuits are linked together when a fire burns it will damage all related components, first you need to remove all burnt areas,
It's expensive but it's also an electronic device.