Bad capacitors in SNES SuperFX cartridges

[Xan]

Recently got an SFC Wildtrax cartridge that has a leaked 22µF/6.3V SMD cap inside. I was able to get this off with the plier twist off method, first wiggled it very gently along the pads, then twisted it off in one quick move, making sure to apply downward pressure. The wiggle part may have been unnecessary or even wrong from what I'm reading. Anyway, it came off completely clean with the plastic part intact, no damage to the pads and the leakage doesn't seem too bad. Is that cap fluid alkaline? If so could neutralize this with some citric acid (most people seem to use white vinegar, but can't stand that smell), otherwise IPA I guess, and put a new cap on there.

The leaked cap turned out to be Panasonic, which you wouldn't necessarily tell when it's soldered on, but the black plastic part has the (M) on the bottom. I have two other SuperFX carts where the caps look and measure just fine, a Starfox and a Yoshi's Island. They both measure 28µF (perhaps higher leakage current from sitting unused for a few years), 1.5 ohms ESR for the Chemi-con "AH" on Starfox, and 0.5 ohms for the cap in the Yoshi's Island. Not sure what brand the other is, but it has a code that starts with "j", which IIRC is Panasonic as well. It seems that at least for the GSU-2 carts they used some very low ESR caps for the time, considering these are tiny SMD parts.

Could also go tantalum for the replacement, but I heard these drop their capacitance when running at nominal voltage, so it might be a bit more work to pick out the best one. The other thing is, the battery on these carts can be replaced with the right battery holder from aliexpress, so it's best to just do that and the cap at once. As to which carts are affected, it seems that every cart with an enhancement chip that isn't the DSP series has the SMD capacitor. Others use thru-hole caps instead.

[jd213]

Yeah, I believe there are certain revisions of Star Fox that are more likely to have leaking caps.

Coincidentally, seems that Virtua Racing on Genesis might also be prone to going bad (same type of caps as the Game Gear).

[Xan]

You're likely referring to the "glob" version of Starfox (which mine isn't), it has the cap on the other side and it always seems to be the same series that fails. I think it's the same cap series as some of the infamous PC Engine Duo caps: https://8bitplus.co.uk/your-consoles/pc ... io-issues/ https://retrorgb.com/star-fox-cartridge ... ncern.html

While I'm not 100% sure, I suspect these are Nichicon caps. They seem to be the only maker that did the plastic base part in that tan color.

[TooBeaucoup]

Interesting to see this post. A few days ago, I was replacing some caps in a few carts just because I was bored and well, they are 30+ year old carts. I decided to do my glob-top StarFox cart. The surface mount cap was in great shape with no signs of leakage. It's interesting how so many caps end up having different outcomes.

[Xan]

Sometimes they just dry up without leaking. It's why an ESR meter is useful.

In one of my PS1s, some of the caps on the CD area of the board are close to 20 ohms, or over, but visually they look just like new. There are still basically no reports on this, but my theory has been that this is at least one cause of reading issues. Hoping to try this out very soon.