To power on, the computer's logic board requires a "trickle" power of 28 V. If the system fails to power on, first reset the PMU. Then follow the procedure below to determine if the symptom is related to the external power adapter.
Note: To verify the power adapter, you need a volt meter. When connecting the volt meter leads to specific pins, make sure the power adapter cable remains securely plugged into its connector on the logic board.
The LED on the DC-to-DC board is a good indication the power adapter is functioning; however, you can further verify the power adapter by checking the voltage at connector J3 on the video riser card.
5. Locate J3 on the video riser card, and check the voltages from the back of the card as shown below.
6. The voltage should read 28 V (+0.5 V -1 V). Make sure the cable is securely seated in connector J3 on the video riser card and at J11 on the logic board.
The testing is complete. You have just verified that the power adapter is not the cause of the "No apparent power" symptom.
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