I have a 15 year old GK MB200 that recently has started to have a frustrating problem. In the middle of playing the amp will just cut out. It still has power but no sound. Sometimes if I giggle the the cord the sound may come back or if I turn the amp off for a few minutes and then back on the sound may come back. I may not have the problem again for a few weeks or I may have the problem the next time I use the amp. I've taken the amp to a shop but they could not find anything wrong. Is anyone familiar with this problem. Thanks.