It is very rare but I have had a couple of AXSBOB boards go bad. Usually I find a bad diode that I can replace. The AXSBOB and AUXBOB are pin out boards for the BMDC. The encoders get their power from the AXSBOB which gets it from the BMDC which gets it from the Motherboard which gets it from the logic power supply. If an encoder shorts, it usually burns the inductor L1 on the BMDC board which protects the 5 VDC. I have used an in line fuse and routed 5 VDC around the burned BMDC by feeding the positive of the tantalum capacitor in a corner of the AXSBOB. This saves a customer $1,200.00 for the exchange of a BMDC. The AXSBOB boards are cheap. Call Alan at my office. He is our parts guy. In the US 1-205-403-9900 or 1-800-245-2598.