Turn on then turn off suddenly

Hi - I found this old device that belonged to my dad ،When I turn on the device, it works normally for half a minute and suddenly turns off. The device works without a battery. I modified it to work on electricity directly from the charger and I am sure that the electrical connections are good It is not a problem of electricity loss

. Could this be the reason or is there another reason in the motherboard? * There is a picture with a warning show up a second before it turns off