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Capacitor missing in Sound Blaster AWE 64

R

Rauli

Experienced Member
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Sep 16, 2013
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114
Location
Spain
I have acquired a Sound Blaster AWE 64 (model CT4520) but after 1st visual examination I have noticed that one SMD capacitor (marked C82) is missing. It's not an optional capacitor, it is broken, there was a minimal piece hanging from its place.

It is placed physically (not electrically) in parallel with another capacitor (C83).

Value of C82 is unknown. Chances are that it had the same value than C83... whose value is also unknown, as it doesn't have any visible code. The only clue is that it seems to be small size (but not the samllest size for a capacitor) and light brown.

Any idea of which capacitor could I use to replace C83?

awe64.jpg awe64c82.jpg
 
Take a close look at your second photo. The two caps are not in parallel--each connects to a different trace on the left.

If you buzz those two traces out, do they connect to the power-supply traces on the edge connector? If so, the value isn't critical. Something like an 0.1 uF at the appropriate voltage would probably do just fine.
 
Yes, I meant their position is parallel, but not in a parallel connection.

The right connection of the missing capacitor goes directly (less than 0.5 ohms) to B1 connection of the ISA bus (12V).

And it seems that the left connection goes to GND (less than 0.5 ohms to screw and back plate).

So, it is just some kind of voltage stabilizer?

Thanks.
 
Call it a bypass capacitor--to keep high-frequency spikes out of the power supply. Strictly not needed for operation. A 0.1 uF (104) 16V or better should do fine.
 
Thanks. I will put a ceramic capacitor, but I must say that I have tested the card without the capacitor (I was afraid of doing it before, but some people asked me to do so) and surprisingly (at least for me) it works! The headphones had a quiet sound, but I must test it again with an amplifier because I want to make sure that there's no noticeable hum or buzz.

Possibly this PC has a very stable 12V line, but maybe I can have problems on another PC with worse 12V quality. If not, I don't understand why there was a capacitor there...
 
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