Atari 800XL and Atari 1050 with shorted power supply!

I recently purchased an Atari 800XL, complete with an Atari 1050 floppy disk drive. Here is the unboxing and the first start… shorted!

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Before turning on a computer that has not been used for years, remember to follow the steps indicated in this video-article.

Tips for buying a vintage computer

Atari 1050 floppy disk drive power supply transformer short circuit test

Unfortunately, the power supply of the floppy disk drive, at 9V in alternating current, does not work and I will have to repair it.

Disassembled internal floppy disk drive power supply transformer Atari 1050

During the test, the power went out! One piece of advice I can give you, when buying a vintage computer, is to do not trust recently untested computers!

Either you buy a computer from a professional, fully tested dealer-repairer, or you should assume that the computer is broken, or at least not working completely. A computer, even if it turns on, could have various problems: the communication ports, the keyboard, the joysticks. You may not hear the audio! The tape or floppy disk player may be damaged.

Before buying a computer, I suggest trying it with the seller, loading games, programs, using all the keys on the keyboard, joysticks and listening to the audio. The test must last some time: defects do not always manifest themselves immediately.

Atari 800XL vintage computer 5V power supply

Having found the floppy disk drive power supply faulty, I don't even trust the computer power supply. We open it before plugging it in. To open the plastic case, there are 4 slotted screws on the bottom cover.

Atari 800XL 5V power supply transformer open disassemble

It seems that the power supply has already been opened, in fact a screw is missing that fixes the transformer. I unscrew the other three screws. One of the pins holding the transformer is also broken.

Atari 800XL 5V internal power supply transformer, components PCB electronic board

Let's test the output voltage. It must be 5V direct current. We also test the power supply under load. We put a 4.7 ohm, 5 Watt resistor in parallel with the 5V output. With this resistance, the power supply should deliver just over 1A. During the test, the resistance heats up. Warning! There is high voltage! If you have no technical experience, avoid doing these tests, which are dangerous.

Atari 800XL 5V power supply transformer disassembled test under load resistance

The voltage test with and without load can also be done from the 7-pole DIN connector, without opening the power supply. For the polarity, you can refer to the pinout of the connector, seen from the contact side.

Atari 800XL 5V power supply transformer pinout 7-pole DIN connector contact pinout, + 5V GND shield

Unfortunately, during the voltage test on the connector, I realized that, by moving the power supply, the output voltage is not always constant. Sometimes there is 5V, other times, the voltage goes down! After a check, I was able to find that the defect is caused by a partially detached solder on a pin of the transformer.

Atari 800XL 5V Power Supply Transformer PCB Faulty Solder PCB 11-2870-005-01, Cold Solder

I apply some improvements to the power supply. I mount a transil on the low voltage output and a metal oxide varistor on the high voltage. These components offer protection in the event of overvoltages or transients that may occur on the power supply network.

Atari 800XL 5V power supply transformer mount transil varistor protection

I mount the metal oxide varistor on the high voltage. It must be mounted after the fuse, if present, or after a thin cable which acts as a fuse.

Atari 800XL 5V power supply transformer mount varistor protection after fuse

I mount the transil on the low voltage. The output is already protected by a 2.5A delayed fuse and the transil must be mounted after the fuse.

Atari 800XL 5V power supply transformer mount transil protection after fuse

Now the power supply is perfect!

Clean the loose styrofoam on the electrical cables

To improve the aesthetics of the Atari 800XL power supply, we can remove the polystyrene that has melted on the cables. Some parts come off just by pulling them. In some cases, the melted polystyrene must be scratched off gently with your fingernail.

Remove the molten polystyrene from the dirt solvent electric cables

If the power supply is disassembled, it is also possible to clean the plastic shell well, with water and a little degreaser. Obviously, no electrical parts must be wet!

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Atari 800XL 5V PSU power supply wash case shell water degreaser

Test the Atari 800XL computer

After trying and fixing the power supply, we can test the computer. I'm too curious to see if it comes on!

Behind the computer connect the power cord and composite video cable.

Atari 800XL retro rear DIN connectors, monitor, power, switch

The 7-pin DIN power connector, with its view facing the back of the computer, has this contact arrangement.

Atari 800XL 5V pinout contacts pinout PSU power connector DIN 7 poles, + 5V GND shield

The composite video cable is the same, with a 5-pin DIN connector, that I use with Commodore computers.

Atari 800XL composite video cable DIN 5 poles TV monitor RCA yellow television

The arrangement of the contacts is the same: the following image depicts the view of the connector facing the back of the computer.

Atari 800XL 5V pinout contacts pinout composite video monitor connector svideo DIN 5 poles, GND, audio, video DIN5

Behind the TV, connect the three RCA plugs: video (yellow) and audio (white and red).

Composite video audio connection behind the LG LCD TV

Let's try to switch on? The computer has booted up! We don't have to leave it on for a long time. We can turn it off right away, to make sure it doesn't smell strange.

Atari 800XL power on boot screen just turned on monitor

After verifying that everything is in order, we can turn the computer back on and test the keyboard. The keys work well, and it is also very nice to press them: the sensation, to the touch, is pleasant.

I test a simple Basic program. In the video, you can see the listing.

The self test of the Atari 800XL

By pressing the key OPTION when the computer is turned on, the self test. Let's test the Atari 800XL!

Atari 800XL option self test memory audio-visual keyboard all tests

The first test we perform is that of memory (memory test). Both ROM and RAM are tested. The test continues until you press HELP.

Atari 800XL option self test memory test ROM RAM

Then, we can test the sound chip (audio-visual test).

Atari 800XL option self test audio visual test voice

Finally, we also try the keyboard (keyboard test).

Atari 800XL option self test keyboard test keys keyboard buttons

Well, the tests are over and everything seems to be working fine. I plan to take the Atari 800XL computer apart to look inside and clean it properly. As soon as I repair the 9-volt power supply of the floppy disk drive, we can also load some games.

Credits: the background music of the video is Jet Set Willy by Rob Hubbard.

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