MHS-5225P Function Generator - temperature controlled fan

[Robbybox]

Hi,
I am just involved with testing my new unit MHS-5225P function generator with power amplifier version.
One strange feature is the fan control. Even if power amplifier is switched OFF the temperature on top of the heat sink rises to more than 50 °C within some minutes, but the fan is not activated. As soon as I switch the PA ON the fan will be activated, even if the temperature is still down.
It looks for me that the fan is never activated in normal mode, and permanently activated in PA mode ON.
Can anybody confirm that behavior?

Another behavior is more critical, that is, in some situations the display shows totally confused characters after pushing any button, and output rises to high values. After switching power OFF and ON again the unit works correct. Some time later that happens again. I can not say from which situation or action this arised. Anybody with similar experience?

If someone need such information:
I have created a placement map for the two PCB inside the box (for most important components), and concerning the fan issue I have developed a simple circuit to get a temperature controlled fan activation, look here (unfortunately in German language only):
http://www.reinhardweiss.de/german/mhs-5225p-fan.htm

Robbybox