kikipcs wrote:Roger. I'll just go for normal Nichicon caps with slightly bigger values to give more headrom on the caps that I noticed are starting to bloat already on this board.
Hm, what do you mean by bigger values? The capacity (uF) rating? Or voltage?
You can go bigger on voltage, although voltage rating directly affects the diameter -- except for the <10uF capacities where they're all small -- so you may have trouble with fit if you go more than one step higher. Regardless, this is usually not a factor in the old ones having failed. Capacitor Plague victims, heat, and end-of-life are. If you want a more robust cap, compare MTBF ratings. You can also look for 105C rating, although that's probably overkill. The more common 85C, even considering the internal working temp of the cap itself, is pretty severe for the inside of a computer.
Do not change the capacity, though. In some (perhaps even most) cases, it won't matter much. But unless you know what the cap is doing in-circuit, it's really best to stick to the uF rating of the original. You have 20% wiggle room by specification, unless the OEMs happen to be tight tolerance (they almost never are), but things tend to use standard sizes: 1, 2.2, 3.3, 4.7, 6.8, 10, and multiples thereof.
kikipcs wrote:Studying lots of eBay and other sites like that I'm 95% sure that the missing cap on the upper side of the board is the same as the others (4,7uF 50V), meanwhile the missing cap in the middle, the C78, is *most likely* a 1uF 50V ( 😕 ) capacitor. Really weird value, so I'll have to delve in the pics a little more.
1uF 50V is an extremely typical value. You may think "what's ever going to use 50V on an ISA card?" And the answer is: Nothing. (Well, maybe a modem.) But, "small" electrolytics -- 10uF and less -- are usually rated 25V, 50V, or 100V. The case size is the same regardless, and cost difference is negligible, so it's common to stock a ton of 50V parts rather than mess with "right-sizing" the voltage rating. 50V is higher than you'll need for most anything except a PSU's mains inlet side, so it's a good catch-all rating. (Although 25V is usually more than enough for LVDC stuff as well, so it's also quite common.)
SirNickity wrote:100uF+ is going to be a bulk cap. 1-10uF will be AC-coupling in an audio circuit. Only common exception to that is video, where the sink end will have a 75R terminating resistor and you need decent near-DC performance for the sync pulse.
Oops. ^^ This guy was confusing the ornament on the top of his neck for the one he sits on. Many sound cards (particularly the earlier ones) are designed to drive headphones and small speakers -- i.e., low-impedance sinks. So, a 4- to 64-ohm load has to work without loss of bandwidth too. That would, indeed, mean you will find larger caps in the audio path. My mistake.