FigTronix

Model 100 Main ROM 27C256 PLCC Adapter

Pictures

This is ONLY for early Model 100's that had a weird main rom pinout, with chip number LH535618.
Late Model 100's and all Model 102's had a standard 27C256 pinout and don't need any adapter.

PCB
Parts

About the parts order:

• It includes enough parts to build 3 boards, because you can't get less than 3 PCBs from OSHPark. If you want to build just one board, reduce the quantities by 2/3.
• It includes several extra 27C256 eprom chips, because they are one-time-programmable, not erasable. I just picked 10 as a generous round number. You can order as few as one chip per board, if you know you will get the programming step right the first time.
• Or, if you can find some uv-erasable ones, you can use just one of those, and delete the eproms from the DigiKey order. You can't get new uv-erasable 27C256 in plcc packaging today, but you can possibly find old stock or used ones. Like these:
  

http://ebay.com/itm/390797004761

http://ebay.com/itm/121899875951

Unfortunately, using this adapter requires desoldering the original socket from the motherboard. it IS possible to do this, without damaging either the motherboard or even the old socket, with flux, solder wick, and patience. Search youtube for "desolder dip".

TODO: Replace this design with one that uses a low profile surface-mount plcc32 socket 28C256. Doing that will mean we have an erasable, reprogrammable part, and it should fit in the original dip socket so we don't have to desolder it. If the combined height of the low profile pin headers and low profile plcc socket are still too thick, then try to find a supplier for edge-clip legs instead of pin headers. Or we can try soldering the pin headers in backwards with just the tips of the long pins soldered in the adapter, and then cut the shoulders and short-sides right off all pins. That will leave you with bare pins with no shoulders, so the board should fit closer to the socket, and maybe that will be enough .