Help! No digital output from Marantz CD94 limited

[Jacky Yen]

Hi!
I need some Help! Recently I purchased a Marantz CD94 limited CD player. Quite strange it uses a single old TDA1541 DAC instead of 2*TDA1541A S1. In my opinion, it sounds just OK!
So I decide to use it as transport player only.

However, there is no any digital signal output from digital RCA or Optical connector. I ask someone to repair it. He changed the SAA7220 (I guess) and check all the supply voltage , well! still the same . Later he use another CD94 and switch replace the circuit boards, finally he told me the "front control panel" may has some function key that lock the digital output .

Really ?? And how to turn on the digital out?
Help needed!!! Really appreciate!
Jacky