It can only be repaired at the factory. The reason the repair work was pulled back to the factory is the complexity of most repairs. They actually run the transponder through the manufacturing line for realignment. Realigning the cavities requires very expensive equipment which most avionic shops don’t have. Depending on the age of the transponder it may not be economical to repair due to the fact that they need to replace the older receivers and in some cases the main processing board. It is important that you talk to the factory before you send it for repair. They can tell from the serial number whether it will be economical. The factory is the best and only place to get it repaired. However, it takes a while to get it there and back. The shipping alone is expensive. We have found that USPS is the most economical.