Our church has a lighted neon sign that is about 25 years old. It has two transformers that each serves (4) 60" bulbs. The problem is that one of the transformers will only last a few months while the other one is an original to the sign. The lighting maintenance falls to me, but after replacing this same transformer 3 times, we hired a sign company to troubleshoot and repair it. Their transformer failed just like the others. I'm looking for troubleshooting tips for the cause of the repeated failures. Any advice is appreciated.