Analysis of repair: for ease of maintenance, mapping out the related circuit, as shown in Figure 1. Elements measured were normal in the illustration, substitution of C1~C4 is not valid. In the trial and found a pattern: as long as the tone control circuit bass control potentiometers placed in the middle position, you do not have protection in advance. According to this law the following changes, write C1 470 μg F/35V, R1, R2 swap to improve V4 cutoff point. According to the above change test machine, troubleshooting.b2Sservice manual download site