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Building an Atari 520 ST power supply

VERAULT

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So I have a couple Atari ST units. Unfortunately the Model 520 I received did not come with the external power supply and they are quite expensive. I recently purchased some din connectors online and want to build my own. Does anyone know of any plans out there to make a quick and simple 520 power supply? Any help in this would be appreciated.
thanks
 

2icebitn

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You're going to actually make a power supply, or utilize an already manufactured something or other? You can use the voltages from an ATX supply. Or you can search for a surplus unit on eBay or from an outlet. Something that's closer in power output to an actual Atari brick.
 

VERAULT

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well thats why I am posting here. Looking for ideas. I would like to avoid using an atx just sitting on my desk.. that would look pretty ugly. I guess I can try and find some bricks with the right voltages as well.

Anyone know the the original bricks posted outputs and amperages?

I guess finding -12VDC on any of my spare bricks is going to be slim to none.
 

fatwizard

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The internal supplies in my 1040 STFs don't provide -12V. I'm kind of surprised to see it listed for the original external supply. I used a small supply from Meanwell, but it doesn't provide -12V.
 

Caleb Hansberry

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VERAULT

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I had thought about using a pico atx psu, but your saying I don't need the -12vdc? So I'm confused. I really only need 5 and 12 volts and that's it?
 

gertk

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If the 520 ST has the TL497 chip on board it does not need the -12V and you can get by with just the +5 and +12 Volt
Use sufficient sized wires for the +5V and GND lines and use both pins in the connector for each. That will keep the voltage drop over the cables and connector as low as possible.

Note: since the power switch is inside the computer, the power supply will run without load when the computer is switched off, not all switched mode power supplies can handle this.
 

VERAULT

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If the 520 ST has the TL497 chip on board it does not need the -12V and you can get by with just the +5 and +12 Volt
Use sufficient sized wires for the +5V and GND lines and use both pins in the connector for each. That will keep the voltage drop over the cables and connector as low as possible.

Note: since the power switch is inside the computer, the power supply will run without load when the computer is switched off, not all switched mode power supplies can handle this.

So in other words disconnect when not in use?
 

VERAULT

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Well I bought a pico atx psu which will give me all the correct voltages. Just waiting for it to arrive from china with the din connectors as well.
 

Caleb Hansberry

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When I was using a ATX PSU with my 520st it would shut down every time I turned on the 520, leading me to believe there was a short on the motherboard. But the problem went away if I turned on the 520 and then the PSU, and it continued to be gone when I used a different power adapter, without this load protection, I suppose.
 

gertk

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Any PC atx supply shouldn't have a problem with no load, no?

ATX power supplies have two seperate parts inside: the main power and the standby power.
In standby the main power supply is off and only the standby power is applied to the motherboard.

If you wire an ATX power supply in such a way that main power is always on you will find out that the output voltages can be off by quite some margin with no load. Some ATX power supplies have 'dummy load' resistors to generate some load and will run.
 
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