Marco we had the same problem at the UK champs last year with ours. It was a problem with the current limiting, we had to get Ian to repair it at Hemel. The adjust things are two pots one for each channel, they set the current limit, both should be the same position. In ours this made no difference to this problem. However it wont hurt to try, clockwise increases the limit and vice versa.

My advice is to contact Ian.