So, now my MB33 is working again as it should.
First of all, I'm very sorry! The last few days I have done two big mistakes:
1. Since my MB33 was completely open I was shure that the audio out is the one direct beside the midi-in. My audio cable was plugged in VCF-in.
2. I had reprogrammed the EPROM, but it was faulty. Now I have burned another EPROM (a different IC) and my MB33 blinks when receiving midi-in.
So, the real cause seems to be the original EPROM-IC. Because the old one is still not generating sounds... Even, if erased and reprogrrammed whith crustypaul's image.
And with the new EPROM-IC (burned with crustypaul's EPROM-image) I can hear the demo song (or better demo sequence) after the Autotune operation.
Strange, but true.
Now I want to thank you very much for help and support!!!!!