1. Not old. Vintage. :)

A New XEGS circuit board Build 3/10/2020



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Well a few weeks have nearly passed, and due to personal issues havn't had a chance to update.
Currently it's not working as I'd not got either an XEGS MMU nor it's ROM.
I did try adding a U1MB to no avail, all the components came out of my spares box so there may well be failed chips among them, and something I'll now do is check them one at a time, in another computer Once I have a known good set I'll retest.

Well it's been powered up, all the voltages checked to each socket, all good..
I've added the 555 timer used in the reset circuit and the 74LS74 in the PAL clock circuit, Reset works fine, checked master oscillator and seeing the input to where Freddie usually plugs in. added a 'Freddie' replacement.. checked and main system clock and now also the PAL clock all good.
Added the rest of the Atari LSI's , a RAM replacement board and a Sophia DVI... Until I got to the MMU & OS ROM ... And... nowhere to be seen.
I'll have to wire in an U1MB to test Doh .. nearly there .. ( Oh and that will be without a keyboard so may have to knock up a TKII and use a PC keyboard until I've decided what to do.. (as no connectors other than power and SIO ( SIO isolated at the moment as no filters added))
I suppose the good news is no magic smoke ... Well not yet anyway ..


Firstly; as all the PDF's now attached to a Resource


I decided to remove all the screen shots I'd been working on.

Secondly; whilst I was in KiCAD and laying out ‘stuff’, I thought I’d better sort out the power switch for the XEGS, currently it uses a mechanical push button, which operates a switch mounted on the Mother Board (M/B), and this is also supported with a small metal frame soldered to the M/B. One problem I have is that the frames aren’t available and the switches are expensive as not used on any other Atari. (unlike the Joystick & keyboard ports (near all & 5200).

So I decided on a more modern take, something that’s found on the 1088XEL computer, a simple push button that latches an electronic circuit switching the Computer on and off. The design can be used on any computer that has an external 5V supply.

The intension on the XEGS is to make 3 or 4 small circuit boards that solder to each other to form the support pillar and switch, these will carry SMD components (only due to size, excepting the power FET). A 6mm square tactile push button will be fitted on the top board to allow the original post that used to operate the mechanical switch to operate it, the side supports for this top board hold the circuit components, and another likely used to connect the original switch holes in the M/B. Although this may end up as being the FET leads.

I’ve included an image of the circuit, but I’ve as yet not built is, and KiCAD wants a circuit diagram for each piece of circuit board used so not being very friendly.


I've now posted the updated Schematics as a resource, hopefully I've found all of the error's however If anyone finds an error please contact me.
Just a quick update of what the board looks like at the moment.
2020-09-18 15.57.06.jpg

WOW Digi-Key parts arrive two day to be processed, shipped from America, and delivered in this country ...

Digi-Key parts ordered.. waiting on BEST.

So Practically finalised the re production of the XEGS Circuit Diagrams, these have taken a little longer, as I’ve been rechecking the bare circuit board I have, against the circuit I’ve drawn.

It’s at least as accurate as I can get with the board I’m using, and although this is rev A. Its look like some of the components are missing off a Version 3 (and bodge wired in) so I’m guessing this is an earlier board.

I hope that I’ve ironed out all of the issues I’ve found, but I may have introduced some other minor errors.

I’ve made sure all the Circuits have the same label names from one sheet to another, thought this would be useful as wasn’t entirely accurate from the one I started with.
I’m still modifying some of the lay out and a bit peeved that I can’t copy from one page to another within the program.
I also got a little fed up just using a PC program and a Multimeter, and Pam got fed up with the Beep Beep Beep..

I’ve been back to the soldering Iron, and ... found I’ve a few components I’m missing.. wish I’d found out before, anyway just been sorting out a Digi key order.

I also need to finish off the order to BEST as I’ve some items to order, along with some items for Richie.

Thankfully I can still build the majority without a keyboard or joystick ports as examples.TK-II can be plugged in for now.

Having drawn the Keyboard circuit and the Keyboards Matrix out, I today spent some time checking through this by opening up an XEGS keyboard.
All the circuitry appears to be good, excepting the wiring shown from the Keyboard Socket on the Mother board, going to the Connector on the other end of the cable. The first pins all seem correct but Pins 9-15 are in the main incorrect including wrong power pins. Just in case of confusion I'm using the Pin numbers printed against the connector on the Mother Board, against those on the PCB connector. I'll recheck again and update my schematics before I post, I'll also check the Matrix but this should be correct and bar the LED the same as 65/130XE.

I've been away this last week, but I did take some of the schmatics away with me, I use labels to show a signal one one page going to another , no different to Jerzy has used. What I've been doing is validating the ones I've used however a few didn't match and I've now found most of the offenders. I've also completed a copy of Jersey's Keyboard Matrix and Keyboard circuit, I'll need to check this against real hardware but I've at least got some drawings to start with, and adjust if required.
I've also update some of the other's already produced in a effort to make these clearer. And when required recreated the circuit symbols, with the Legs of the chip in an order that allow the diagrams clarity, However I can't remove all the crossing over that sometimes happens. I've also created a symbol for the Modulator.
That's about it for now.

So I've now been opening each of the schematics, any issues I've been slowly resolving, I'd found a fair number of issues the power supply page now shows Four separate points that have individual filtering, rather than three, I added the PAL clock circuit which was missing entirely, made sure that the components have their correct designations to match the circuit board, and of course the correct Values.
I’ve created new symbols so I now have a library with all the Atari LSI's, used along with usual components, capacitors, transistors etc.
I’ll add parts to this in line with some of the upgrades I intend to produce, such as the O.S. Controller, PIA/VIA extension boards etc.
I’m having a few issues with some of the labels that have been used, i.e. say a Label for D0-D7 appears this will be the same and easy to check across all pages, however not all of these match up correctly so I’ll have to go through them all and validate on each page.
I’ve also not reproduced the keyboard schematic nor the keyboard matrix, the matrix is easy as the same keyboard as a 65/130XE but the circuit board in the keyboard itself needs to be reproduced, similar to the rest of the Atari’s but does signal it’s presence so it starts BASIC with the keyboard attached, or Missile command if not (on a standard XEGS we are talking about)
I’ve just noticed I’d not put the modulator on any page, I’ll have to tack this on a page with some space.
However the main work is completed.

Well I've finished producing the main drawings in KiCAD now, I do have to recheck some bits as some part directly copied from the original's produced by Jerzey Sobola.

Things still to check. All the Power references need to check if it states +5A or +5B it is actually from that branch, the same with all the global tags, I need to go through each drawing and make sure inputs / outputs, bi directional and all the names match. Also the resistor networks have their values swapped about and even wrongly associated that’s still to do and update plus I'll add the pin each is on. ie RP1-1 first resistor on RP1 and RP3-5 5th resistor in RP3 as an example

For now I'll attached them:-
Update Deleted see https://atari-owner.com/club/resources/xegs-circuit-diagrams.68/

Famous last words well not just yet I hope, but plans made not come to light as yet..
I was looking to build up several of the circuits with a view to powering it up..
Except there were no drawing of the PAL clock circuit among the schematics I have draw up by Jerzy Sobola. Hence I've spent most of my time checking and double checking,
One the values used two where they are and the component identification. And then drawing up the schematic (still to do)
Somewhere I got sidetracked..
I however I have completed most of what I'll describe as the main schematics

Power (this includes Audio and Reset circuit on same sheet as well)
Memory decoding (ROM, MMU, 74ls138)
CPU’s (SALLY, ANTIC, FREDDIE, Master clock)
Video (GITA, 4050, Along with discrete components, |Colour adjust)

I’ve still a lot to do, however some of these are easier to do such as the RAM memory, keyboard cross connections etc.
The main ones I’ll need to do next are those with PIA & Pokey on them.

Deleted see https://atari-owner.com/club/resources/xegs-circuit-diagrams.68/

Well not a great deal completed on the XEGS Board see Below, however finding evermore issues with the circuit diagrams, with the same lable such as C55 being used for both a decoupling capacitor 100nFor 0.1uF (should be C60) and a 100uF electrolytic capacitor, and thats just one example, finding a few components extra shown on Diagrams, along with those missing ..

Deleted see https://atari-owner.com/club/resources/xegs-circuit-diagrams.68/

I needed a break for a bit, going from soldering iron, to KiCad on PC back to soldering iron etc..

I'll have another go, and finish off the PAL clock circuit along with the Colo(u)r adjust circuit, I may even check voltages and plug in some components and see if it boots to Basic 23/8/2020 Oh I forgot I'll need the reset circuit finished as well :facepalm:

I've spent some time reproducing Jerzy Sobola's circuit diagrams, I've not gone to far, and one I still have to correct all the part labels as the the colour adjustment circuit was a copy of the 130XE and bare no relation to those labels in the XEGS.

Deleted see https://atari-owner.com/club/resources/xegs-circuit-diagrams.68/

I've actually started on the build, fitted a few sockets for I.C's I knew will be needed. started on the Power input circuit, came to doing the capacitor's....
Well I've produced a list based on ME removing them from a completely trashed board some while back, and as some parts of the circuit will now be redundant, such as the branch going to the modulator, I 've been going by the XEGS circuit diagrams produced Jerzy Sobola, I did know, there were several small anomalities, for instance one bit of the diagram was copied from the 130XE diagram complete with all the wrong resistor, capacitor etc labels
As I was comparing them, and fitting components as I went, I found evem more issues, however they are a great starting point, but i'll now be redrawing them in KiCAD
I've reproduced this, some may note that we have two capacitors marked as "C2" as an example.
And C13 the 'wrong C2, (left of C4) and C3 are all next to each other, and electrically directly connected, C3 however is correct, and C1 on all three XEGS I have is 1000uF not 470uF.
L4 and C45 & C46 are not required.
View attachment 1117

Here is the original much broken XEGS
XEGS Many damaged traces.jpg

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 as above and the Media Album has now been deleted.

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.

As mentioned above I'll have to do these correctly in KiCAD.

The three main upgrades will be –
PokeyMAX for stereo
Sophia or Sophia2 for DVI Video
Maybe something like this
XEGS Addons.jpg

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 If the Sophia2 turns up then I won’t need any PAL colour clock nor any colour adjustment circuitry (to be checked)
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."
Actually Newly draw ones.

Having viewed the Circuit diagrams, the first I looked at was the DRAM see Below
View attachment 1116

It appears that none of these components will be used, so saving a bunch of 33 Ohm resistors and the DRAM

Updated 7/07/2020
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.

Famous last Word's
"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."
They will all be reproduced, but corrected for the boards I have

I'll be adding more to the Blog Soon