Atari XEGS Mods & Upgrades

XE Game System console without its keyboard

The Atari XE Game System (XEGS) console is essentially a complete 65XE without a keyboard, but its board and connectors differ from the computers'. Its 64 KB of RAM is in two 64K × 4 DRAMs, where the XL/XE computers use eight 64K × 1 chips. The NTSC and PAL consoles have phono jacks for composite video and audio in place of a monitor port, and no version has the ECI connector of the XE computers sold in Europe. TFHH's hardware notes add that the XEGS has no Parallel Bus Interface (PBI) port either.

The procedures below summarise the cited articles and makers' instructions. Read the full instructions before desoldering anything, and see Atari XE Game System General Maintenance for opening the console.

Chips the upgrades use

XE System console chips named in the upgrade instructions

Chip	Part numbers	Used by
CPU (SALLY 6502)	C014806	Stereo board (address line A4, pin 13)
ANTIC	C021697 (NTSC); C021698 (PAL and SECAM)	512 KB SRAM board, which plugs into the ANTIC socket; PAL conversion
GTIA	C014805 (NTSC); C014889 (PAL); FGTIA C020120 (SECAM)	512 KB SRAM board; stereo board; PAL conversion
MMU	C101686	512 KB SRAM board
FREDDIE	C061922 or C061991	512 KB SRAM board; jumper W2 for PAL conversion
POKEY	C012294	Stereo board
ROM	C101687, 32 KB: XL OS revision 4, Atari BASIC revision C and Missile Command

Identify each chip by the part number printed on it. The redrawn board schematic repeats some U-numbers; Atari XE Game System Troubleshooting Guide lists them.

Video and audio output

All versions of the console have a phono video jack carrying composite video and a phono audio jack. The NTSC console also has an RF output with a channel 2/3 switch; PAL consoles have RF on channel 4 (PAL B) or 36 (PAL I) with no switch. A monitor or television with a composite input connects to the jacks without modification, unlike the Atari 2600, which needs an internal tap such as the Atari 2600 Composite Video Mod.

Atari brought separate luminance and chrominance (Y/C, the signals S-video uses) out only through the 5-pin monitor port of the XL/XE computers, on pins 1 and 5, and the NTSC and PAL consoles have no monitor port.

SECAM consoles for France have no television jack. They have Atari's 6-pin SECAM monitor port as well as the phono video jack, and were supplied with a cable from the monitor port to a Péritel (SCART) plug.

SECAM monitor port (6-pin DIN socket)

Pin	Signal
1	+12 V, 5 mA maximum, for the SCART slow-switching (AV mode 4:3) line
2	RF modulator audio, about six times the normal audio level
3	Péritel/SCART audio
4	Composite video, SECAM
5	Video ground
6	+5 V, 100 mA maximum, to power an RF modulator

Memory upgrades

Current's FAQ groups memory upgrades by banking scheme. The 130XE standard gives 128 KB in total and uses bits 2 and 3 of PORTB to select one of four 16 KB banks.

XE-GM1 kit

Innovative Concepts of Warren, Michigan, sold the RAMdrive + XE-GM1 in 1988 for US$34.95. It takes the XEGS from 64 KB to 128 KB with true ANTIC banking, compatible with the 130XE. The kit held two 41464 RAM chips, a 16-pin custom IC, two sockets for the RAM chips, wire and a few resistors, with five pages of instructions in 26 steps and a hand-drawn schematic. A disk carried Atari DOS 2.5 with RAMdisk software and a RAM test by Glenn Smith of Radon Software.

Matthew Ratcliff fitted one for Antic in about three hours and described the work in this order:

1. Desolder the two original RAM chips without overheating them or the board, then clean out and inspect the pads.
2. Solder in the two RAM sockets. Ratcliff refitted the original RAMs and ran the self test, then repeated the test with the kit's RAMs, before going further.
3. Stack the two pairs of RAM chips, with pin 16 of each top chip bent out, and solder them together. Use a light, quick touch and let each pin cool.
4. Bend out all the legs of the custom IC except pins 8 (ground) and 16 (+5 V), and solder it piggyback on U13.
5. Wire resistors to pins of the PIA, and a resistor between pin 16 of the top RAM chips and a pin of the custom IC.
6. Run wires from the custom IC to the PIA, ANTIC, RAM and FREDDIE. Two pins of FREDDIE are desoldered and lifted.
7. Test the board before closing the case.

The review does not list the pin connections. Ratcliff left a gap of 1/32 to 1/16 inch between each pair of stacked chips so that they ran cooler, which the instructions did not mention. The wire in the kit had insulation that melted back during soldering, and he changed to Teflon-insulated Kynar wire. He then ran memory tests for over 24 hours without a fault.

The XE-GM2 kit from the same company takes an XEGS that already has the XE-GM1 fitted from 128 KB to 192 KB, again with true ANTIC banking. Ratcliff also reported in August 1988 that ICD had said it was working on an XEGS RAM kit similar to its RAMBO XL for the 800XL.

512 KB SRAM board (tfhh)

Jürgen van Radecke (tfhh) makes a 512 KB static RAM board that he lists for the 800XL, 1200XL, all XE models and the XEGS, though not the 600XL. It plugs into the ANTIC socket and carries ANTIC on top. At power-on it runs in 512 KB RAMBO-compatible mode; his SETMEM.XEX utility switches it to 256 KB Compy-Shop mode, which is 130XE compatible with separate CPU and ANTIC access, or turns the expansion off. Pressing RESET while holding START puts it back in 512 KB mode.

The V4.5 instructions for the XEGS are:

1. Desolder ANTIC and fit a machine-pin socket. Some models need two stacked sockets for height.
2. Desolder the MMU, C101686 on the XEGS, if it is not already socketed, and fit a socket. Remove any solder residue from the ANTIC and MMU pins.
3. Plug ANTIC into the socket on the expansion board with pin 1 to the left. After soldering the wires, plug the whole board into the ANTIC socket on the main board.
4. Bend up pins 6 and 16 of the MMU so that they stay outside the socket, and plug the MMU in.
5. Solder the four wires of the supplied cable as in the table below. For FREDDIE and GTIA, put a drop of solder on the shoulder of the pin and solder the wire to it; do not desolder those chips or lift their pins.
6. Check for solder bridges and that every chip has pin 1 to the left. Switch on with nothing else connected. The XEGS should start Missile Command. If no picture appears, switch off at once.

512 KB SRAM V4.5 wiring in the XEGS

Wire	Connects to
Orange	MMU pin 16, bent up
Red	MMU pin 6, bent up
Brown	FREDDIE (C061922 or C061991) pin 4
Black	GTIA pin 12; on a SECAM FGTIA (C020120), pin 20

To remove the board, lever up the end that holds ANTIC, a little on each side, with a flat screwdriver until it comes free; do not pull on the larger part of the board. The maker's product list says three wires must be soldered, while the V4.5 manual's cable has four.

Other projects

Michael Current's FAQ lists two more internal projects that name the XEGS: Bernhard Pahl's 256 KB upgrade for the 800XLF, 65XE, 800XE and XEGS, with Atari Magazin and Compy-Shop modes, and the Satantronic 1 MiB SIMM expansion by Dodo (Jozef Friedmansky) for the 800XL, 800XE, 130XE and XEGS, which also offers 256 KB Compy-Shop, 256 KB Atari Magazin and 64 KB 130XE modes. The same list gives ctirad's RAM 320XE/576 as for the 130XE, 800XE and 65XE with ECI, which the XE System console does not have.

Stereo sound

TFHH's Stereo Enhancement board, a dual-POKEY design, is listed for all XL, XE and XEGS machines. Its instructions cover the board dated August 2015 and are written for XL, XE and XEGS machines together, without positions specific to the XEGS.

1. Remove the POKEY (C012294). If it is soldered in, desolder it and fit a machine-pin socket.
2. Plug the stereo board into the POKEY socket with its solder pads at the top, turn the main board upside down and shake it. If the stereo board falls out, replace the socket with a machine-pin one. A second socket can raise the board clear of other parts.
3. Plug the original POKEY into the board's lower socket, pin 1 to the left. It gives the left channel and keeps the keyboard, SIO and paddle functions. A second POKEY in the upper socket gives the right channel; only its sound section has to work.
4. Connect pad A4 to pin 13 of the CPU first. With only that wire fitted the computer should start normally.
5. Connect pad GTIA to GTIA pin 15, for the keyboard click and beeper, and pad SR to pin 6 of the LM358, the small 8-pin chip near the RF modulator, which feeds the right channel into the standard audio output.
6. Take the LEFT, RIGHT and GND pads to line-level jacks or an existing hole in the case, using shielded cable. A switch from SW to ground selects mono.

NTSC to PAL conversion

TFHH's PAL Injector board generates the 4.43 MHz colour burst clock that a PAL GTIA needs, for NTSC machines that lack those parts. A full conversion also needs a PAL GTIA (C014889), a PAL ANTIC (C021698 or C014887) and, in an XE or XEGS, a 14.187 MHz system crystal; a VBXE board supplies its own clock and removes the need for the crystal. The board plugs into the GTIA socket and the PAL GTIA plugs into it. It does not work with the SECAM FGTIA.

On the 1200XL and NTSC 800XL that the maker checked, GTIA pin 16 is left open. On the XEGS it is linked through jumper W2, to the right of FREDDIE, usually by a 0 Ω resistor. Remove the link, or the converted console gives no colour or does not start. The link can stay out if the console is later returned to NTSC.

Faulty PAL GTIA

Some PAL GTIAs in XE computers are faulty, most often in the 800XE. The fault shows in some games and demos, for example the spaceship sequence at the start of Rescue on Fractalus, and on the GTIA test screen of KMK's SysInfo. TFHH's GTIA Fixer, built to a 2010 circuit by Simius, plugs into the GTIA socket and carries the faulty GTIA. The GTIA has to be desoldered first. The maker lists the board for all XL, XE and XEGS machines.

Keyboard extension cable

The XE System Keyboard's cable is short, and two brackets on the keyboard case lock under the front of the console. Ratcliff describes the keyboard connector as a standard DB15 female. Ratcliff made an extension cable so that he could type with the keyboard on his lap. The FAQ gives the console's keyboard port as a 15-pin D male plug whose pin numbering is the reverse of the standard.

XE System console keyboard port

Pin	Signal	Pin	Signal
1	/K2 keyboard scan (POKEY)	9	+5 V
2	/K1 keyboard scan (POKEY)	10	+5 V
3	/K0 keyboard scan (POKEY)	11	KBDETECT (GTIA/FGTIA)
4	/KR1 keyboard response (POKEY)	12	Not connected
5	/K5 keyboard scan (POKEY)	13	Ground
6	/K4 keyboard scan (POKEY)	14	Not connected
7	/K3 keyboard scan (POKEY)	15	Ground
8	/KR2 keyboard response (POKEY)

Ratcliff found a small board inside the keyboard with resistors, capacitors and two CD4051 chips that pass key codes to POKEY in the console, which does the scanning.

Sega light gun conversion

Before the Atari XG-1 was sold separately, Ratcliff described converting a Sega light gun for the Atari. Cut off the Sega connector and solder the wires to a 9-pin joystick connector:

Sega gun to Atari joystick port

Sega wire	Atari joystick port pin
Blue	1 (stick forward)
Grey	6 (trigger)
Green	7 (+5 V)
Black	8 (ground)

The XEGS ports are close together, so do not use a female 9-pin connector with "ears". An old joystick cable may not do, because Atari joysticks do not use +5 V and usually have no wire to pin 7; Ratcliff suggested a joystick extension cable with all nine pins wired. The converted gun fires when the trigger is released, because the Sega trigger works the opposite way to Atari's. To correct it, remove the five screws, one of them under the Sega logo on the side, and rewire the three-terminal trigger microswitch to its normally closed contacts.

Hard disk interface

Sijmen Schouten's MyIDE interface, sold as a cartridge or for internal fitting, connects an IDE drive to an XL/XE computer and needs a modified XL OS. Separate internal versions were made for the XL/XE computers, the 1200XL and the XEGS.

Parallel bus

The XEGS has no PBI or ECI connector. Ratcliff found that the PBI routines in the XEGS operating system ROM are intact, and suggested in 1988 that a builder could add a custom PBI connector and use ICD's MIO board. TFHH's Sys-Check, which needs a PBI or ECI port, cannot be used in the XEGS.

Related pages

• Atari XE Game System
• Atari XE Game System General Maintenance
• Atari XE Game System Troubleshooting Guide
• Atari XE Game System Capacitor Replacement Guide
• Atari XG-1
• Atari 65XE
• Atari 130XE