07/07/2020 Some Changes
I originally created a Media Album to go along with this Blog, however after consultation with both Matt Baker and Tim Kline; going forward I will be adding pictures as I build and test as I go along, these will appear within in the Blog itself, for now the Album still exists
I'll add photos including the original Circuit Diagrams produced by Jerzy SOBOLA
I will gradually build this up with information as to the upgrades included from the start, along with those bits I'll be leaving off of the original board. I'll reproduce the Circuit showing what components have been left out.
The three main upgrades will be –
PokeyMAX for stereo
Sophia or Sophia2 for DVI Video
Possible internal upgrades for later on
TKII PS/2 keyboard interface
MIDI / S2 or X2 Synth
CF or SD Card interface based on 1088 XEL/XLD interface.
The build, will also make use of 64K static memory rather than DRAM, and a replacement for Freddie unless the Sophia2 turns up then I won’t need any PAL colour clock nor any colour adjustment circuitry
Well A few of my Build thoughts.
As I'll be using an SRAM module from Lotharek, Neither the DRAM chips or any circuitry that supports them will be required, I'll be posting modified Circuit diagrams showing the components I'll be leaving out.
Having viewed the Circuit diagrams, the first I looked at was the RAM on 'XEGS4_DRAM' https://atari-owner.com/club/media/xegs4_dram.149/
It appears that none of these components will be used, so saving a bunch of 33 Ohm resistors and the DRAM
I'll be using high quality turned pin sockets for all of the components throughout, along with very good quality decoupling capacitors for each IC fitted, I'll be adding those I need initially along with few items recovered from a broken XEGS mother board. I'll be building up the power circuitry first and making sure this has a nice and clean output, most of the parts will be new, however power switch and one of the inductors will be re used. Sockets will be fitted for CPU, Antic, GITA, Pokey, PIA, 74LS138 address decoder and MMU, O.S for connection of U1MB. (https://lotharek.pl/productdetail.php?id=56 )
The 64K Base Memory (Static or SRAM) will sit on a daughter board supplied by Lotharek (https://lotharek.pl/productdetail.php?id=291) in the CPU socket, with the CPU plugged into this.
All of the Video circuitry from the LUM0-LUM 3, Csync, & Colour lines on GITA will for now be left out, as the Sophia will produce its own output on DVI independent of GITA itself. If Sophia 2 is available then I'll not even need to supply a PAL colour clock, as this is inbuilt to Sophia 2 (and replaces GITA entirely)
Freddie is used to provide a clock via a divider chain, along with DRAM refresh signals, I hope to replace this with a custom divider or there is a Freddie replacement to go with Lotharek's SRAM replacement (https://lotharek.pl/productdetail.php?id=233) which has a divider chain built in, along with the DRAM refresh which is not needed and may introduce noise.
Quick note as that as I've been reading and checking Jerzy Sobola's schematics I've found a number of errors, some will be slight different between versions of the XEGS, however some area's appears to be copied from say the 65XE, 130XE with the same component references. I'll try and correct these but I will have to reproduce from scratch.
I'll be adding more to the Blog and the Media Album Soon