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Thread: Building an Atari 520 ST power supply

  1. #11
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    Jan 2012
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    Connecticut, USA
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    Quote Originally Posted by gertk View Post
    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?

  2. #12
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    Jan 2012
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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.

  3. #13

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    Quote Originally Posted by VERAULT View Post
    So in other words disconnect when not in use?
    Yes, just switch off the supply at the primary side (mains switch).

  4. #14

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

  5. #15

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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.

  6. #16

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    OK that's interesting. I am lead to believe most consumer grade switchers can handle, at least for a time, a no load situation.

  7. #17

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    Quote Originally Posted by 2icebitn View Post
    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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