[Mondial]

At his point I really think the LED is working as it should and the MPX decoder may need work or alignment. After all, you don't know if the MPX or stereo indicator worked properly before the bulb burned out either.

Do you hear any stereo effect when receiving the strong station? If there isn't enough 19 kHz signal to turn on the lamp fully, there isn't enough to activate the decoder circuit and you will only get mono.