S. Kluger El Paso RCPM (915) 598-1668 El Paso, TX, 08-27-82 The following is a modification to the GODBOUT Z-80 CPU board to enhance it's reliability and is applicable for all boards REV J or earlier. I was given this mod by CompuPro today, did the changes and it works great..... The Z-80 CPU may have a problem addressing the on-board sockets if they hold HM6116-compatible RAMs. The problem I encountered and fixed with this mod was the following: I am using an old Hayes 80-103A modem card with a hardware modification to decode the lower 8 address bits. The port is 90H. When addressing the board using Z-80 I/O instructions (LXI B,9090H, COUT A), everything worked fine. Using 8080 I/O, it did the following: It deposited (read closely) the RAM page number (F8 or above) at PAGE+PORT. Example: at F890H it wrote a F8, at F990H it wrote a F9, at FA90H it wrote a FA, and so on. It did that only on RAM chips plugged into the CPU board socket. This is what you'll have to do to make your board work: 1. Connect a jumper wire from U15 pin 1 to U14 pin 1. U14-1 may be connected to Vcc. If so, remove the short to Vcc. 2. Connect a jumper wire from U14 pin 2 to "A" of J2. 3. Break trace going TO "A" of J2. Please note that "A" of J2 is wrong in the schematic but right on the board. In the schematic, "A" is "B" and "B" is "A". This mod removes "pwr" as write strobe for the 6116 and replaces it with "mwrite". I was also told that REV J and earlier boards MAY not work right when converted to 6MHz operation.