I've had the same with the blue LED in the UcD180AD; it did not affect the sound in any way. I replaced the LED, which died again after about two weeks of operation. Again, the operation was not affected. Probably something wrong in the circuit which drives that LED, but unrelated to the performance of the amp itself. I stopped worrying about it.
Thanks for your reply but this is engineering - there has to be a reason that this has happened. LEDs have a life of, like, ten million years, so I have doubts that it has failed. Something else is wrong with the UCD 400HG and I do not know what.
This upsets me.
I suppose that because I am a scientific kind of bloke I have trouble dealing with a failure that is both unexpained and seemingly without consequence. It upsets my delicate sense of order, the part wouldn't be there with out a purpose, and it has failed. Therefore, something is wrong.
What I want to know, despite the seemingly inconsequential consequence of the failed nice blue LED I would like to be able to pin-point what has happened to account for the failure of this component. Write it off to pure OCD.
If anyone has any idea what is going on, however irrelevent it may seem, I'd be obliged if anyone could shed some light on this issue...