I'm working on Detex HD2500 PCB and I noticed that negative side step is not working like positive side step. Did you find any error on this PCB/schematic. In the same time I found that there are a missing additional transistor than in the yamaha schematic. And also I'm confused in the same time because in another schematic from powertech HD3600, which is almost the same schematics with Detex hd2500, negative side step is working properly. Where is the problem?