Hello,
I might have misunderstood the information given in earlier posts, but my conclusion based on what I have seen is that the card is working per design. It could be that the input specification does not match your requirements. Our input is 50 ohm matched and is expecting a 50 ohm source impedance, but might also work with other sources. A photodiode might require a different, or additional pre-amplifier of buffer. If you let me know what input characteristics you require we can look into the possibility of a specific build option.
Best Regards,
Peter