Hi mates, thank you for your kind help.
The mixer has this problem, after boot it shows repetitive high peaks for about 2 minutes (on speakers sounds like a short "tic tic", it's about about twice a second, but not regular. After about 2 min they start drastically reducing and the led go normally to zero, the sound od fource may then be visible on leds. Curiosity: After 2 minutes, only if I activate the mic1 I can still hear some tic tic, but they also reduces too.. till disappear. The mixer then is working regulary. Chances are if I switch off and on soon it keeps work perfect, but if I wait some time it will do the same problem. The problem is then connected or to the temperature of one component or to the lack of capacity of one/more condensers.
The mixer was working every day about 17 hours, but in really ideal conditions, I can suppose the problem is connected to lifetime of some components. For example I noticed the C1201 was a bit "fatter" and I substituted it, as well as C1213 & C1206, C1412, and from that time the situation seems a bit improved, before the problem didn't disappear, now yes after 2 minutes.
I can't replace all condensers, also it's dangerous to do because it's not easy to remove them and the pcb may be damaged.
If I have to guess, that "tick" looks a reset of all the ADC, maybe the CPU is expecting something from them and still resetting until receive a proper answer.
There were others strange behaviours: in test mode it showed "software version 0", then accessing the update mode (but without updating it) it showed correctly 1.32, then again in test mode was correctly shown 1.32. I tried also to upload again firmware. When the software version was 0 in test mode I couldn't make test of fader and other sliders, the led were always off, now is ok. Probably when the problem was present in test mode I couldn't test all the trim potentiometers, so the problem is probably on the analog board, maybe I've to remade the joints of the flat cable?
Here is the video I made:
Thank you a lot for help