PIO port replacement
The PlayStation PIO port is difficult to work with, because of how brittle it can be, and how difficult it is to find mating connectors.
For reference, the connector on the motherboard is a female one, and the connector on the carts are male, even though this is counter-intuitive a bit.
This online store managed to find an actual manufacturer for the original connector, and is stocking them. This is a great opportunity for developers and enthusiasts alike, in order to build custom PIO carts for the PS1.
This connector almost matches the shape and form required to properly plug into the console. Using a dremel or any abrasion tool to remove the triangles on the edges would render the plug a perfect fit.
However, if this connector is used to replace the PIO port of the console, then both the above plug and normal cart plugs can be used to connect to it. It's a perfect replacement for the console's connector, if you remove the two plastic tab on the bottom.
Ideally, one would replace the motherboard connector with a VHDCI connector, in order to be backward compatible with the other carts. Unfortunately, finding a connector that has a matching footprint is proving difficult.
However, there is a pair of connectors that have a proper footprint, and are an almost perfect fit: a female connector and its matching male connector.
Both plugs are completely symmetrical, and one can use either on the motherboard, or the cart that would plug into it. Note that this means the cart would fit horizontally instead of vertically, which makes for a better mechanical stress, and enables the usage of digital probes more easily.
These connectors are much more solid than the original PIO connector, and don't seem they would break too easily. The connection is hard to make and requires a lot of force, which is probably a good thing, to avoid spurious disconnections.
The motherboard's SIO connector sits a bit too close, and the new connector is slightly too wide, so one needs to remove a bit of plastic in order to make it fit snugly:
Also, the motherboard is slightly too long, and one might want to remove a little bit of pcb in order to make the connector sit flat. Otherwise, the following would happen, which isn't a problem per-se, as the connection is still tight, but the plug will then sit at a slight angle:
The console will properly close with this plug in place, but since the new connector is slightly wider, a little bit of plastic hides the bottom corners of the connector, preventing a full proper mating, unless removed:
