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Thread: My Official Genesis power supply is putting out much higher voltage than listed.

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    Nameless One BRNexus7's Avatar
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    Genesis My Official Genesis power supply is putting out much higher voltage than listed.

    I was curious to see how much voltage the power supply actually puts out and I was getting a reading of 13 volts for the 1602-1 power supply. It is listed as a 10v power supply. I checked my 9 volt radio shack power supply and got a relatively accurate reading of just a little over 9 volts, so its not a problem with my multi meter. I know the Genesis takes it down to 5v's internally, but I don't know if I should be worried about potentially damaging my console if I continue to use this power supply.

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    ToeJam is a wiener Hero of Algol Guntz's Avatar
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    I thought old PSUs like the Genesis AC adapter needed some kind of load before doing a voltage test. Try testing the voltage while the AC adapter is powering the Genesis (you'll have to take it apart).

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    Nameless One BRNexus7's Avatar
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    Where on the board can I take measurements? Also, wouldn't the reading be 5 volts since the Genesis uses a 5 volt regulator?

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    The medium-sized mang. Raging in the Streets Lastcallhall's Avatar
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    There's about 10-11V measured on the 7805s coming in. Well within tolerance and it's all stepped down to 5V anyway. No need to worry.

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    Nameless One BRNexus7's Avatar
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    Quote Originally Posted by Lastcallhall View Post
    There's about 10-11V measured on the 7805s coming in. Well within tolerance and it's all stepped down to 5V anyway. No need to worry.
    Just curious why it reads 13 volts when simply plugged into the electrical outlet. Thanks for the info.

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    The medium-sized mang. Raging in the Streets Lastcallhall's Avatar
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    Because there's no load.

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    Nameless One BRNexus7's Avatar
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    Then why is my modern 9 volt Radio Shack adapter reading 9 volts through the Power outlet instead of something higher like the Genesis adapter? Is it just the way modern adapters are designed?

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    The medium-sized mang. Raging in the Streets Lastcallhall's Avatar
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    It really comes down to power efficiency. I wouldn't say it's the way modern adapters are designed, but in a way, it is. The 80s sega brand adapter probably was spec'd under the notion that 1) it should deliver somewhere between 7V and 25V to fall within tolerance ranges for the 7805 and 2) was made to overshoot the rated 10V (or 9V, depending on model), knowing that it would be stepped down anyway. I don't know what the efficiency is on the RS one, but if it's delivering 9V with no load, then there's a good chance it's under 9 with full load conditions. But again, as long as it doesn't drop under 7, you should be ok.

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    Nameless One BRNexus7's Avatar
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    So you can go up to 25 V's before running into problems? WOW, that is a high tolerance level. I guess I really don't have to worry about anything if that is the case.
    Last edited by BRNexus7; 08-20-2015 at 05:26 AM.

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    Road Rasher AlmostOriginal's Avatar
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    I have been working with power supplies for a while now and this is what i have learned. The original Sega Genesis power supply consists of 3 parts:

    Transformer
    Rectifying diodes
    and a Resistor.

    The reason the voltage is so high is because much like the mains voltage the power coming out the transformer is not stable ac. It is fluctuating from like i don't know +?10?VDC to -?10?VDC. So if you would have to measure the voltage from the transformer you would get an average reading from your multi meter. Then you have the rectifying diodes that converts the AC to DC and there will also be a small voltage drop of like 1,2 V (Thats common for diodes) Now you have a DC output. But it is now fluctuating between 0 - 10 VDC. (This will not power the sega unit) Then you have the capacitor that is going to smooth out the unregulated DC to a more smoother output. The output will mostly vary depending on the load and size of the capacitor. When you measure the output with a multimeter (no load) you will get the top value of the dc output. But as soon you put a load to the power supply it will drop like 2 Volts.

    Your new 9V power supply is a different story. It uses switching technology, so you can power it with like 90 - 250V. Since it is is switch mode it will have a pretty stable output. Closer to the output you desire.

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    Road Rasher Xalphenos's Avatar
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    Quote Originally Posted by AlmostOriginal View Post
    Your new 9V power supply is a different story. It uses switching technology, so you can power it with like 90 - 250V. Since it is is switch mode it will have a pretty stable output. Closer to the output you desire.
    @BRNexus7 this is really the short of it right here. The readings you are getting are whats to be expected from their respective technologies.

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    Co-Creator of the MegaAmp Raging in the Streets villahed94's Avatar
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    Quote Originally Posted by BRNexus7 View Post
    I was curious to see how much voltage the power supply actually puts out and I was getting a reading of 13 volts for the 1602-1 power supply. It is listed as a 10v power supply. I checked my 9 volt radio shack power supply and got a relatively accurate reading of just a little over 9 volts, so its not a problem with my multi meter. I know the Genesis takes it down to 5v's internally, but I don't know if I should be worried about potentially damaging my console if I continue to use this power supply.
    That voltage is without load, and it will surely go down when loaded (console on). There is no real risk about the voltages (as long they stay below 20-25V) except the higher the input voltage, the hotter the internal regulators in the Genesis will get.
    I personally use a PS2 Slim PSU as it's lower voltage and capable of powering a Genesis with all the add-ons.


    Mega Amp: The reference audio circuit for the Sega Genesis/Mega Drive.

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