Hi Fabio,
First the error/patch is really only relevant for very large seldom used (1MX8 EPROMS). None of the common 24 or 28 pin EPROMS/EEPROMS are affected. The U100 & U101 RAM/Flash ROM section is fine and should not be changed.
The cut should be as near as possible to pin 1 of U4 (front of board). This is joined to pin 1 of U121. The connection from U121 pin 1 onwards to K23 & K26 should be cut (front of board) and a jumper to pin1 of K23/K26 connected to U8 pin 7.
Pin 1 of U4/U121 should be then be connected to bA19.
Good luck with your build
John
From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of Fabio Battaglia
Sent: Sunday, February 9, 2014 2:18 AM
To: n8vem...@googlegroups.com
Subject: [N8VEM-S100:2378] Patching the S-100 PROM/SRAM Board V1
Hello group,
I'm approaching the stage where I'm ready to build my first S100 boards, and I'm reading up the documentation for each board on S100Computers.com before start soldering anything.
There is something which isn't completely clear to me about the PROM/SRAM board described at this page (I have a V1, the schematics are numbered V2-2).
At the bottom I read that the board has pin 1 of U4 and U121 miswired to bA18 instead of bA19 (U8 pin 9), and that I should cut the trace and rewire it correctly.
I'm checking the board, and I see the following:
From U8 pin 7 (bA18) starts a single trace which branches through a via and goes to U11 pin 5, while the other branch goes to U4 pin 1, U121 pin 1 and headers K23 pin 1 and K26 pin 1.
The question is, do I have to
1) Wire only U121 and U4 pin 1 to bA19 and keep K23 and K26 wired to bA18, or
2) cut off the second branch entirely (U121, U4, K23 and K26) and wire everything to bA19?
I guess it's the first one, which involves two cuts and two wires (a cut after the branch and a rewire to bA19, another cut after U121, before K23 and a rewire to bA18) but I want to be sure before doing any damage.
I hope I have explained myself well enough, If not, tell me and I'll try again.
Thanks,
Fabio
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