If it's not there I wouldn't add it. The board is marked + and withe for negative.
Thanks! thesteve confirmed to me that if the 100uF cap is not present, it should not be added. He also recommends using ceramics for everything but the audio section.
Could someone please identify which caps are part of the audio circuit?
I tried all ceramics on my SNES, but
the pitfall was the Composite/S-Video amplifier/output circuit...
SNES engineers used 2 x 100uF capacitors in parallel to achieve 200uF before the signal leaves for the TV and replacing that area with ceramics led to disastrous results: white screens would lose sync, weird artifacts, just didn't work right...
Long story short I had to switch back to regular electrolytic caps for those video circuits, I just used standard 220uF caps so I wouldn't need 4.
Steve did consider the 4 100uF ceramics I used as defective from the factory because my DMM with capacitance measuring rated them at 60uF, but I don't think that was the only problem...
Kinda didn't trust the large ceramics after that, the small ones under 10uF are usually accurate in reflecting their labeled value. Electrolytic caps are usually higher than what the label says by default and lose said value over time as heats dries the fluid or it leaks out.