Atari 800XL Power Supply Replacement

The 800XL's 7-pin "POWER IN (DC)" socket and its ON/OFF switch, at the right-hand end of the rear panel

The Atari 800XL has no rectifier or voltage regulator of its own. It runs from an external supply that plugs into a 7-pin DIN socket, J7, and Atari specifies that supply as +5 V DC ±2 % with a maximum rating of 1.2 A. Whatever the supply delivers goes through the power switch S1 and three filter networks straight to the chips. A supply that fails high therefore damages the computer: Terry Stewart's 800XL lost two RAM chips to a supply that was delivering 7.6 V. The usual repair is to test the original supply and, if it is out of limits, replace it with a modern regulated 5 V supply wired to a 7-pin DIN plug.

Atari's parts list gives the 800XL's supply as CA024814-001. The comp.sys.atari.8bit FAQ lists the North American XL/XE supply as Atari C061982/CA024814, 5 V DC at 1.5 A, in four case styles, and warns that the third, the solid black "Ingot", "can damage the computer if not turned off quickly" when it fails.

Symptoms

• The machine is dead and the power light does not come on. Atari's symptom checklist gives the power LED, the power supply and the cables as the causes.
• A snowy picture. Atari lists a defective power supply among the causes, with the TV switch box, the power and channel switches, the RF modulator and the RF cable.
• Hum bars on the screen with an Ingot supply. The FAQ's advice is to disconnect it.
• RAM test failures that come back after a chip has been replaced. Terry Stewart's 800XL showed a RAM error, ran correctly after he replaced the chip, and then failed again with a second dead RAM chip after he tried its original supply.

A dead machine with a good supply points at the computer: Atari's checklist also lists shorted parts on the +5A, +5B and +5C lines and shorted ICs. Work through the Atari 800XL Troubleshooting Guide if the supply tests good.

Safety

• The original supply is a mains unit; Atari's US supply takes 110 V AC. The one Terry Stewart opened had its transformer and board set in potting compound, and he could only get inside by cutting it apart. A supply cut open this way exposes its mains wiring; do not connect it to the mains again.
• Measure every supply, old or new, at its plug before it goes near the computer. Nothing on the 800XL board limits the voltage.

A failed 800XL supply cut open by Terry Stewart: the inside is potted in compound. It had been delivering 7.6 V.

Tools and parts

• A multimeter with DC volts and continuity ranges.
• A regulated 5 V DC supply rated for at least the 1.2 A that Atari specifies for the 800XL. The FAQ notes that supplies with a higher current rating are usable and often run cooler. The retrohax.net build used a Mean Well GST25A05, rated 5 V at 4 A.
• A 7-pin DIN plug. The retrohax.net build used a Deltron 610-0700 (7-pin, 270°).
• A soldering iron and solder.
• As an alternative to building a supply, Best Electronics sells a rebuildable 5 V 1.5 A supply under the Atari number C061982/CA024814 for the 600XL, 800XL, 65XE and 130XE.

Procedure

Atari's figure 1-8: the power socket seen from outside the computer. Pins 1, 4 and 6 are +5 V; 3, 5 and 7 are the ground return; pin 2 is ground.

Test the original supply

1. Unplug the supply from the computer and plug it into the mains.
2. Set the meter to DC volts and measure between pin 1 and pin 3 of the supply's plug. Atari's figure 1-8 shows the socket face as seen looking at the computer; the plug's face is its mirror image.
3. Repeat between pins 4 and 5 and between pins 6 and 7. Pins 1, 4 and 6 are +5 V and pins 3, 5 and 7 are the ground return.
4. Compare each reading with Atari's limits, +5 V ±2 %, which is 4.90 to 5.10 V.
5. Retire a supply that reads above 5.10 V, and retire an Ingot supply even if it reads correctly, given the FAQ's warning about how it fails.

Check the computer's power input

Atari's schematic of the power input: J7, the power switch S1, the filter capacitors C1-C15 and inductors L1-L4, and the three rails +5A, +5B and +5C

1. With the supply disconnected, set the computer's power switch to on.
2. Measure the resistance between pin 1 and pin 3 of the computer's J7 socket. On the schematic, pins 1, 4 and 6 run through S1 to the +5 V side of C1, and pins 3, 5 and 7 go to ground.
3. If the reading is close to zero ohms, the +5 V side is shorted. Find and repair the short before fitting any supply. Sams gives this as a gate for the Atari 130XE, whose J7 is wired the same way: if there is a short, do not fit a new power pack until it is repaired. Atari's checklist names shorted parts on the +5A, +5B and +5C lines and shorted ICs.
4. With the switch on, check continuity between pins 1, 4 and 6, and between pins 3, 5 and 7. Each group should be joined. No continuity from pin 1 to C1's positive lead with the switch on points at the switch S1.

Wire the replacement supply

The solder side of a replacement plug on the retrohax.net build: three pins bridged to +5 V, three to ground, the middle pin left free

1. Cut the original output plug off the new supply.
2. Identify the +5 V and ground leads with the meter. On the retrohax.net supply the lead with the white stripe was +5 V, but the author warns that this may differ.
3. Bridge pins 1, 4 and 6 of the DIN plug and solder the +5 V lead to them.
4. Bridge pins 3, 5 and 7 and solder the ground lead to them.
5. Leave pin 2, the middle pin, unconnected, as the retrohax.net build did. On the 800XL board pin 2 goes only to the shield.
6. Before fitting the shell, check with the meter that there is no continuity between the +5 V group and the ground group.
7. Plug the supply into the mains and measure between pin 1 and pin 3 of the new plug: 4.90 to 5.10 V, positive on pin 1.
8. Fit the plug shell.

First power-up

1. Set the 800XL's power switch to off and connect the new supply.
2. Switch on. With no cartridge and no powered disk drive the 800XL starts in Atari BASIC.
3. Run the built-in self test: hold OPTION while switching on, with no cartridge fitted. Do not leave a self-test screen up for more than about seven minutes; it has no attract mode and can burn the screen.

Testing

Supply checks after fitting a new supply (Atari pin assignments)

Test point	Expected
New supply's plug, pin 1 to pin 3, unloaded	4.90-5.10 V
6502C (U8), pin 8 to pin 1 or 21	+5 V
ANTIC (U7), pin 21 to pin 1	+5 V
GTIA (U17), pin 27 to pin 3	+5 V
POKEY (U22), pin 17 to pin 1	+5 V

In the self test's memory test, two long bars stand for the 16 KB operating system ROM and 48 blocks for the RAM, 1 KB each; a good segment turns light green and a bad one red. The remaining 16 KB of RAM is not tested. If a segment is red after running on a faulty supply, see Atari 800XL RAM Replacement.

Supplies for other Atari 8-bit machines

The 600XL, 65XE, 130XE and XE Game System use the same 5 V DC supply as the 800XL; the FAQ also lists a 5 V 1 A supply, C070042, for the 65XE and XE Game System, and European 5 V versions such as C061763. The Atari 400, Atari 800 and Atari 1200XL take 9 V AC from a transformer instead, and do their own rectifying and regulating.

Related pages

• Atari 800XL
• Atari 800XL Troubleshooting Guide
• Atari 800XL General Maintenance
• Atari 800XL Capacitor Replacement Guide
• Atari 800XL RAM Replacement
• Atari 800XL Computer Field Service Manual