Behringer SRC2496 issue

Hi all, i searched around but it's seems old posts where I can't found proper solution.. I have an ULTRAMATCH PRO, after working with Minidisc, Laptop to connect with a decent audio output to my stereo, I seen that the left output channel is more quieter rather than right channel... already tried with different cables or sources, no change...

I tried to quick check the inner board. but seems quite ok, there is anything that I can do/check? if it's gonna be too complex I'll take a good optical to RCA converter.... but maybe here there is a good expert that can guide me to upgrade/provide good maintenance...

thank you very much in advance..

Igor