Thanks for responding to my problem.
TX & PX I connected correctly. USB to RC232 converter is tested on other devices.
when connected to the power supply, the device does not boot
yes my Khadas does not power USB ports for a USB mouse
Voltage AO_5V normal.
fuses F1 (500mA) and F2 (900mA) are OK
VCC5V is missing
HDMI_5V_EN always 4.9V
Also, my laptop does not see it when I try to launch a firmware update (while holding the power button while connecting to USB)
for power, I used a proven power supply, applying a voltage of 5V to the DCIN input and using a regular monitor. With this connection option (external power supply), it worked for more than two weeks.
I could not confuse the polarity, because I use the connector with the keys
after what happened, I specifically once again checked the power supply for possible power surges when switching on and off. But found nothing - the power supply is working fine