badmojo wrote:
You're correct in that it doesn't seem to bother the card at all, it works fine as far as I can tell. It's me that's bothered, knowing I'm using broken hardware.
Could you please explain a little more what "VDD +5 digital power supply pins for the AD1848" means? Why was that cap there if it wasn't required for the card to work?
Good question, and I don't think there is a single answer.
The Analog Devices audio codec has separate power supply pin groups for sensitive analog circuitry and digital circuitry. The two big electrolytic capacitors are far more than what is suggested in the datasheet as recommended capacitance for digital circuitry supply, but also electrolytic capacitors are a bit worse suppressing high frequency spikes than the recommended ceramic capacitors, so basically you need bigger electrolytics to match for the ceramics. If it were the only bulk capacitor for digital power of the AD1848, it might not even work, or if it were the only bulk capacitor for analog power, you might hear increased noise or it might not work.
Now why there are two overly large capacitors there, I don't know. Usually two smaller capacitors in parallel is better than one large, so maybe that's why there are two. Maybe the capacitors were initially smaller, but someone noticed the design has few of these and few of those capacitors, and asked if they just use one single type of 47uF/50V electrolytic capacitor for everything as it is easier and cheaper to manage.
Many times you just see empty slots when a part is not necessary and it is just left out. Sometimes somebody just comes up with a random guess for big enough capacitor and that's it then, there is very little point to waste time in doing complex calculations or measurements what is the minimum capacitor it still works with when you have better things to do.
So basically, it's not that broken, and is not degraded much, and is not going to break more if you keep using it. I still suggest replacing the capacitor, for peace of mind and resell value.