Why does vim3 need to connect to the gpio 5v power port to start the android firmware?

The development board I use uses the official power supply, and uses hdmi to connect the screen. After I burn the ubuntu and Android firmware, the screen does not light up normally. Maybe the system does not start.

When I use the serial port board to connect the development board vim3 (5v, gnd, rx, dx), the screen lights up and the system starts normally. After many tests, the vim3 development board needs to be connected to the gpio 5v Port to start the system. As shown in the figure below。
What is the reason?

@Maxsheng You can measure the capacitance corresponding to the red arrow in the figure below to see the corresponding voltages?

When I plug in the 5v gpio port, the system starts normally. The capacitor voltage at this time is shown in the figure below.

When I start up without plugging in the 5V GPIO port, the system cannot start properly, and the voltage of the capacitor is unstable at this time. Sometimes larger than 5v, may reach 7v, 8v; Sometimes 2v, 3v; It is changing dynamically.

Is this a development board hardware problem?

Hi Goenjoy,
C3/C4 was the INPUT;
C6/C7 was the OUTPUT;

Hi Maxsheng,
Glad to receive your feedback!
With the official firmware, VIM3 will sets the PD adapter voltage to 12V input during startup. The C3/C4 will be 12V; Then the C6/C7 will be 5V;
Therefore, I guess your situation now is:
1/The firmware is incorrect, causing the PD adapter to fail to output 12V;Lead by indirect the C6/C7 will not be 5V(or <5V). Then the HDMI will not work.(HDMI need the 5V to work)
2/U2 is probably broken,and cannot provide 5V output.
So,you can try something:
1/Use the official firmware to try again.
2/Use a 12V normally powered adapter to power the board.
Hope this helps you.

I have encountered the same problem. My solution is to unplug the HDMI interface and plug in the USB power supply interface. At this time, the development board starts to run, and then plug in the HDMI interface

@Totti thanks
The firmware I use is Android 9 downloaded from the official khadas website. And the power adapter I use is also official. If I do not connect the 5v gpio port, the white LED in the middle will flash when the power adapter is powered on. I don’t know whether this phenomenon means that the system has been started.

1/I have tested the latest firmware and found that Type-C input is 12V; So you can measure whether your board also inputs 12V when it is turned on;
2/The white LED in the middle will flash means that the system has been started;

@Totti How can I test the voltage of Type-C input?

In the above discussion, I have described the voltage conditions under various states.

You can test the voltage of C3 when the white LED flashing.

@Totti As described above, Sometimes larger than 5v, may reach 7v, 8v; Sometimes 2v, 3v; It is changing dynamically. At this time, the screen is not displayed

If it’s a hardware problem, I can find the seller’s after-sales service.

Theoretically, there should be no such variation in input voltage;You can try using a stable 12V power supply to power the VIM3.