Help me with designing a toslink output circuit

[Mp3]

Hi everybody,
i have a yamaha keyboard here with a dead left+right output but the headphone out works.
first i need to see if the DAC or if the output jacks is damaged.
Anyway i wanted to add a toslink output if i am in there working on the DAC.
should i break off the signal from the L+R input pins on the DAC to avoid conversion to analog. or should i pull it off the dac outputs?

Then i was thinking about using one of these cheap USB SPDIF DAC, but would it work if i pulled off the usb from the board and wire the dac inputs to it...
https://www.ebay.com/itm/DAC-Decoder-PCM2704-USB-Audio-Sound-Card-Module-Analog-SPDIF-Coaxial-HiFi-Decord/182843205108?hash=item2a924de5f4:g:IygAAOSwigRa2wG7

[dmills]

Odds are good that the problem is the socket (Connectors are almost always the way to bet with MI gear).

I would be very surprised to find the DAC on that keyboard had separate L, R INPUTS, they almost all use some variant of I2S or its similar kin.

Assuming one of the usual sort of SPDIF interface chips (a CS-something or other?) you will need Data, LRCLK, SCLK and (probably) a MCLK at 128 or 256 times the audio sample rate, these are most likely available on the DAC chip.

Regards, Dan.