As gaming hardware gets older, finding replacement parts gets harder and, therefore, more expensive.
It's for this reason that we've seen a bunch of community-made replacements, one of which is the Open Source Expansion Pak (OEXP), a replacement for the N64's Expansion Pak which aims to provide a cheaper alternative to the real deal by combining two 2MB RAM chips rather than using a single (harder to come by) 4MB module.
The project is a noble one, but it hasn't been without its problems. Back in December of last year, Swiss modding and repair company Consoles4You reported that the current PCB design was flawed and could actually kill the N64 console it was inserted into.
"Since I own some RAM chips, I decided to order some oexp PCBs," says Consoles4You. "Unfortunately, testing the first pcb instantly fried my n64. The issue is that the edge connector is designed symmetrically, but the real connector is larger on the left side. Depending on how the pcb factory cuts the pcb the oexp pcbs will instantly short all pins, killing the n64. I've already redesigned the edge connector + fixed a few more errors on the pcb and will order more samples soon."
Later the same month, Consoles4You stated that the PCB had been redesigned to avoid the issues. However, we're still seeing reports that the OEXP is frying N64 consoles:
Consoles4You insists that the latest redesign solves this issue.
As noted by the original creator of the project, the total cost is pretty close to what it costs to pick up an original Expansion Pak – so unless you have a burning need for a replacement, it might be worth keeping your distance from this project until the community is completely positive that its problems have been fixed.