Check out these links:
1. DE Flipper Issues: http://www.pinwiki.com/wiki/index.php?title=Data_East/Sega#Flipper_Issues
2. If LED bulbs, it could be the type of bulb used for replacement. I specifcally use the Twin 2835 SMD bulbs from Comet: https://www.cometpinball.com/ProductDetails.asp?ProductCode=25-pack-2SMD-CT-FT
However, if you ask 100 people on LED bulb choices, you'll get 100 different answers.
If you have any pictures, that could assist as well.