K8081 Powerblock - PIC IC issues

Two years ago I bought the K8081 power block for an outdoor project. I have connected an Visaton Exciter to the output so the amplifier and speaker can be build in to protect it from the rain.
The power block worked for an while, but broke after an couple of months. The relais that is turning the amplifier off is clicking every 5 seconds. So When an input signal is presented, the relais clicks and the amplifier is turned on so I can hear music. Then after 5 seconds, the relais is clicking again and the amplifier is shut off. Then after an other 5 seconds is goes back on and this proces repeats as long as there is an signal presented on the input. When the signal is off, the amplifier shuts off as wel (or does not turn on).
I’ve replaced the PIC IC that is inside already once. This solved the problem for an while but the problem came back.
So I bought an new kit because the problem could be somewhere else that in the PIC. This is not the case. The power block shows the same problem after an while again. Exact the same behavior.
I’m an little bit out of options now, so maybe someone here can help me with this. The alternative is to remove the PIC and to hard wire the port that controls the Relais, to be always on. Not an pretty solution, but better than no sound at all.

It is possible that the problem is related to the fact that the unit is used outdoors.
Anyway, we do not have the means to solve this issue from a distance.
We suggest to return the amp for inspection/repair to:

Velleman Projects.
Legen Heirweg 33
9890 Gavere
Belgium

Please include a detailed fault description.