I am working on another 58 and I have the manual for the 58 but this manual has no parts or mention of the OB part that must have been an afterthought. Does anyone out there have a OB input card schematic for the XLR section of this machine? There is also a separate power supply that is on the opposite side with two fuses on it. It provided plus and minus 20VDc to the input card. It is working so I will not need that. Here we go again with lack of documentation. First the 238S and now this.