Surface Noise Reducer Problem:  THD LED does not illuminate with any setting of THD control nor any level or type of music being played.

Probable Cause 1:  Your power is 110-120 VAC (not Europe), and you forgot to set the power supply voltage switch to 120 V.

Solution 1: Set power supply voltage switch to 120 V.

Probable Cause 2: The music you are playing to adjust the THD control, should be loud and full of highs, like a trumpet fanfare or clashing cymbals. 

Solution 2: Try another section of the record.  If a section with such sounds cannot be found, set the control in the middle.

A good check to see if he circuitry and LED is in basic operation can be performed as follows:

* Remove one of the input connections from the SNR by simply pulling either the left or right RCA plug out.
* Then play some loud music from any source, record, tuner, etc.
* With the Quieting control set in the middle, you should be able to adjust the Distortion Limiting control to make the THD LED illuminate.