Hi Jose, the issue is found, the problem came from the RF section , there is a signal named HPON , normally this signal is 5V and is coming from the 5.2V power supply RF section , the signal was strangely corrupted with 100Hz like a rectifier output.
and actually this was the case ,the output capacitor C4 (30000 ?F 20V) in the A8 schematic and A 23 mother board was completely dry. so no smoothing capacitor. it is a large capacitor from cornell dubillier, externally in good shape but the value is only 10 nF.
thanks for your interess
PS: the serial number begin with 24 so a unit from 1984 nearly 27 years I guess if it would be safe to change all the other capacitor in the power supply? any advice ?
ON1EV
Guerrino
