Amiga CD32 was getting black/gray screen after 2-5 minutes.
The voltage at the voltage detector (U14) was getting under the threshold of 4.3V, which causes that the reset signal was pulled down, and causes the black/grey screen.
I replaced the Voltage detector (u14), the 10K resistor (R629) and capacitor (C629). The last two just as precaution.
The machine is working again, tested it for 1,5 hour.