Marshall JVM 410 no sound / switching relay problem

[prulup]

Hi, I have a problem with Marshall JVM 410. It plays fine but sometimes (after some channel switching or longer playing and then changing channel) the sound goes out. I localized the problem, it goes out on the VOLUME section. Some sort of switching relay problem as I can see signal on the input of CON8 but nothing (short to the ground) on the output of it. Sometimes all the channels goes out, sometimes only some of them. I can hear relays, I can see proper LED colours, all the tubes are 100% good. I measured the voltages on CN206 and this seems to be the core of the problem. They are not the same when the amp works and when it is faulty. Where should I search now, IC306 or the transistors TR2xx? Or elsewhere? Many thanks!

[EL34]

posted in wrong board.... moving