spdif input defective?

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Recently I bought a very old dac (Sphinx Project three.)
It has 3 spdif inputs, 1 optical and 2 rca types.

When using the optical input the dac works good (very good is probably a better statement for a 15 year old device, i prefer it over my sony sacd).

But when i use either of the electrical inputs it only works properly when connected to my (also old) tascam cd player. With the new sony there is a lot of distortion/noise.

Does somebody have an idea what might be wrong, I suspect there is a mismatch between the old and new devices, maybe something like a dc offset?
 
I can think of at least two possible causes;

* (perhaps too obvious?) Your Sony SACD is not properly configured to output 16-bit 44.1KhZ PCM (only), thus the signal is not understandable at all to the old Sphinx dac.

* There might be something wrong with the input buffer circuit; there might be a DS9637 dual line receiver (or similar) sitting directly on the inputs, and converting the signal to 0/5V.

So if you can rule out the first problem, I would take a closer look at the input circuit(s) and perhaps look with an oscilloscope (if you have one handy 😉 )
 
No, i don't have a scope handy :bawling:

There are 2 chips near the inputs, a cx23053 and an saa7220.
The cx23053 is the receiver but it's too old; it is impossible to find any documentation.
I'm going to try and replace the rca inputs with torx 173s.
 
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