The current, no-longer-produced board offers a compact design, but the machined pins are both hard to source, and tend to require a ton of patience to get placed on the pcb correctly, as they need to make contact with both the top and bottom of the PCB. We'd like to remedy this problem by removing the need for machined pins, and instead use the more easily sourced header pins. Then there's an issue with the space constraints of the original Apple Macintosh 128k, 512k logic boards - There's no space to utilize the headers for jumpers reliably. Installation of the original board, while it does technically fit, is far too snug a fit - leaving less than 0.25mm of headroom when sliding the logic board back into the system. In addition to this issue, there's no way to easily access the power cable when the mod is installed. We'd like to re-layout the board and provide a better solution.
This project initially started as a means of building up the original design and selling kits, since the original developer (Big Mess 'O Wires) no longer produces the kit. After having built 3 of the boards, and having none of them work quite right, with some logic lines not making proper contact with the machined pins, we started looking for a better solution. The issue with the original design is that the machined pins must make contact both on the top and bottom of the pcb. The bottom appears to only provide a place to solder the pins in place, and do not connect to anything electrically (this will be examined in the original schematic), while the bottom pins which make contact (or don't, as is the current situation) are the electrically conductive pins. Additionally, the ROM sockets aren't level in the final product due to how the tops of the machined pins are secured, and the socket's plastic juts out. This isn't ideal, as the final product looks janky. This also introduces a problem when installing the sockets themselves, as they don't sit level, and getting them installed properly can be a chore in patience.
Moving on, the jankiness of the sockets not being level brings another problem to the table - the small constraints between the metal chassis and the mod board - leaving less than 0.25mm of free space, which, when combined with the jumper pins, ends up causing an issue - you cannot use jumpers at all. Now, whether or not this is an issue with the particular length of the machined pins we have, or if it's a known issue remains to be seen. When the original mod board is installed, it appears to be installed as flush as possible with the logic board's ROM sockets, leaving little room for installation error. This provides such little room for working around the board itself that it poses a risk of breaking the mod board when reinstalling the logic board into the chassis, as there is no room for error.
When the original mod board is installed, any jumpers attached to the board will come flying off as the chassis shears them off. It would be ideal to provide a board that has enough clearance to allow the use of jumpers, so that the board can be easily installed or removed without needing to re-solder it in place (right?). In this re-design, we hope to move things around a bit and ensure that we can utilize all the free space above the logic board to accomodate a better design.
The initial design idea is to move the ROM sockets out onto arms that go off to the side of the central board, thus providing ample space for any clearance problems. Ideally, the new sockets would be installed upside-down (measurements to be done to confirm there's enough space). In addition to this, the jumpers would be moved and recommended to use right-angle jumper leads, so that when the mod is installed, they will face up when the logic board is slid back into place. We may still use the machined pins, but they will be connected electrically on both sides of the board, so as to remove any possible signal issue.
The ROMs and code will continue to use the original code. The only change is the hardware layout.