Answer.                                                                                                                                       The TH150DP lighting transistors are rated at 100ma. The Intermountain F7 units use 4 bulbs in parallel for lighting. Each bulb draws 30 to 35 ma. The total being 130 to 140 ma.  This exceeds the the 100ma rating of the transistor on the decoder. The lights will  typically work for a short time, then the transistor fails and the lights stop working. Present production runs of the DP5X decoder (formerly TH150DP) decoder use a higher current transistor and can handle the 4 bulbs.  If  the lights on your TH150DP has failed as a result of this,  please return them to TCS packaged in a small box. The box will prevent the 8 pins on the board from getting bent and damaged during shipment. Please include a note saying "Intermountain F7 failure. Please repair lights with higher current light transistors."  This will remind us to be sure to use  the correct transistor to repair or replace the decoder.  TCS will cover cost of return shipment. For return mailing information click on "Contact TCS" button below.