TRS-80 Model I EI question

From: Richard A. Cini, Jr. <rcini_at_msn.com>
Date: Mon Jul 14 18:52:51 1997

Hello, all:

        I'm trying to track-down a mod that Tandy on the Expansion Interface. On one
of my early EIs (SN# 000352), there was a 6-pin DIN modification, which
someone at one time told me was to correct some erratic signal problems.

        So, I called Tandy and ordered the EI service manual, but it only applies to
the "new" PCB version (units with SNs 035000 or greater). Does anyone have the
schematics to the original one and can check pin functions?? Internally, the
board is labelled "1700077-C", does not have the green conformal coating, and
has the RAM chips right next to the power supply section.

        Mod 1 is on IC Z17 (LS157), pins 1 and 8 (GND)
        Mod 2 is on IC Z24 (LS32), pins 4 and 7 (GND)
        Mod 3 is on IC Z22 (LS367), pins 12 and 8 (GND)

        Matching the old ICs and pin numbers to the new schematics produces the
following:

        Mod 1 is for the MMUX line, Mod 2 is for WR* and Mod 3 is for INT*

        Can anyone verify this?

------------------------
Rich Cini/WUGNET
   - ClubWin Charter Member (6)
   - MCPS Windows 95/Networking
Received on Mon Jul 14 1997 - 18:52:51 BST