Hello free_electron!
Thank you for answering.
The 7805 is working fine 5,XXVolt and no overheating.
I bought the device with this fault. Don't know if somebody used the RS232 connector.
Can't find the MC14568, only a LT1180A (Low Power 5V RS232 Dual Driver).
You can hear three "beeps" in the video. This is not always the case. Sometimes I power on, it beeps, display turns on, turns off and that was is.
(no second or third beep)...