Raspberry Pi Zero No LED Lights – Checking PAM2306 for 3.3 V

If your Raspberry Pi is dead and there are no LED lights then this multi-page article will help, however you need to start from the first page in the sequence to begin diagnosis. The green status "Act" LED D2 relies on the 3.3 V rail and therefore if it does not light up, then it is worth checking the presence of this voltage rail.

The Raspberry Pi Zero uses the PAM2306 integrated circuit (IC), which is a dual step-down dc-dc converter that establishes two voltage rails. The PAM2306AYPKE version takes 5 V at the inputs and produces 3.3 V and 1.8 V rails. It supports input voltages as low as 2.5 V and as high as 5.5 V and can only step-down. The output current can be as high as 1-ampere per channel, and there is automatic shut-off in case of a short circuit at its output. The switching frequency is typically 1.5 MHz, however in the event of an output voltage short circuit it becomes 400 kHz. Thermal shutdown occurs when the die temperature exceeds 150 °C. During this time, the IC remains in a reset condition until the temperature drops to 120 °C

In this application, the first channel produces 3.3 V through pin 8 (LX1) and the current passes through a filter coil L1. The channel enable pin (EN1) is tied to the 5 V rail, and therefore pin 8 produces 3.3 V immediately.

Checking for 3.3 V

To check the presence of 3.3 V, set your multimeter to measure DC voltage, and connect the black probe to test point PP5, and the red probe to test point PP8, shown in the header section diagram of this page.

The absence of voltage, or abnormally low voltage, indicates two possible scenarios; it could be that PAM2306AYPKE is damaged and no longer operating correctly to produce the correct voltage. Alternatively, it could be that there is another IC connected to the 3.3 V rail that is short. The only way to be sure is to isolate pin 8 from the rest of the circuitry, and then measure the voltage at pin 8. If the 3.3 V returns then it is another IC on that rail that is short. If the 3.3 V remains absent then it is very likely that PAM2306 has failed.

Please note that there will likely be newer variations of this board with different circuitry. However, if it uses the same IC, then you will have to use similar principles outlined in this article. Currently, due to financial difficulties, I am no longer working on the Pi Zero.

This Article Continues...