So the bad news is that audio takes some effort to diagnose properly, and some more bad news is that Tekken 2 and its generation use SMD caps, which aren't as easy to start with if you're replacing caps. The good news is Tekken 2 is pretty inexpensive and plentiful, so you could get another one if you screw it up. It also comes in 3 parts, all of which go bad, so you can hang onto the spare pieces and have backups.
The bottom-most board has all the sound caps, chips, etc. It could be anything in the sound chain... bad sound rom data, bad audio custom, bad d/a converter, bad op-amp, bad amp, bad caps, bad potentiometers, etc. I had fuzzy audio on a similar board, and it was caused by a bridged pin on the audio custom -- looked like from the factory too! It honestly could be a fine pcb, and the wiring, cables, etc. in your cabinet could have issues instead. Is it a cab? Supergun?
Hell, it could be your pcb's audio settings. This pcb does stereo and mono, and the pinout is in the
manual. If you're just using a jamma harness, make sure the board is set to mono in the test menu.
I usually check everything that doesn't require taking off components, first. So check the mono/stereo settings, check your wiring, check supergun audio attenuation settings if you're supergunning it. If none of that helps, sure you can recap it. Just recap everything, you might as well, there aren't that many. Smokemonster replaces them with
through-hole caps, so you could do that if you wanted to avoid SMD ones.