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Thread: Sproggy Supply: Almost Working...

  1. #1
    Constant Bitrate
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    Sep 2001
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    Post Sproggy Supply: Almost Working...

    Hey guys... I'm gonna need some help on this one.
    I just finished my Sproggy PSU (it's an MK 2.6 w/ Power Good and an ATX connector). Everything seems to work, except I only get 1v on the 3.3v line.

    My first though was to replace the max788 IC with a new one, which I did, and it failed to solve the problem.

    I know the circuits for the Max78* are exactly the same, and I can't imagine that I have a bad inductor or resistor on the 3.3v side...

    Does anyone have any ideas?
    Is the LM2587T-3.3 from National an equiv. (I've got some of those laying around if you think it might work)?

    I'm also running the PSU off the 12v line from my current system (just a tap off the PSU). Is it possible that its not giving me enough amps to power the system? I can get the HD to spin up if it's the Motherboard isn't plugged in, and I can't get the MB to boot if it's the only thing connected (but that probably has to do with the 3.3v line).

    Any help is greatly appreciated.
    Thanks,
    -Miles
    Near Completion: Intel P166 MMX, 32MB ram, 13GB Hard Drive, Keypad, 4x40 LCD. Sproggy MK2.6 ATX PSU. Win98SE with Winamp and Mark Zehnder Plugin. (Web-site: very soon)

  2. #2
    Constant Bitrate
    Join Date
    Jul 2000
    Location
    Israel
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    134

    Post

    Try to replace the MBR745,or maybe it's not so good isolated from heatsink - and therefore causing to short-circuit.
    Also,it may be a problem of power-good circuit. Disconnect the input to CMOS4049 and then try to measure the voltage.
    About LM2587-3.3 - you want to use it for 3.3v? It can only supply 1.5A...not like MAX788.
    And try to connect your whole setup to car battery,and then see if you have problems operating the PSU.
    Enjoint life!

  3. #3
    Constant Bitrate
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    Sep 2001
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    Post

    Thanks for the tips Dima:

    I tested the supply without any heatsinks so I was sure that there was no short (no heat without a load, so it doesn't harm anything).

    The Power Good circuit is on the 5v line, so that's not a problem.

    I don't have an extra MBR745, but I'll try to get a new one if nothing else works.

    I'll also try to plug in the supply to my car later (going to work right now).

    I'll let you know how it goes.
    Thanks a lot,
    -Miles

    PS: the LM2587T-3.3 says that it outputs 5A in the datasheet. are you sure?
    Near Completion: Intel P166 MMX, 32MB ram, 13GB Hard Drive, Keypad, 4x40 LCD. Sproggy MK2.6 ATX PSU. Win98SE with Winamp and Mark Zehnder Plugin. (Web-site: very soon)

  4. #4
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    Post

    I might be wrong,but isn't an ATX mobo's power good signal is 3.3v?
    And 5A of LM2587-3.3 is switching current,it's capable of giving short bursts of 5A,but RMS current is 1.5A max.
    If you don't have any luck with MBR745,try to build the 3.3v circuit as stand-alone,without any others circuits.It might be a problem of wiring and/or connections with other sections of PSU.
    Enjoint life!

  5. #5
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    I'm building this supply along with my friend... He completed his tonight, we tested the 3.3 line and it worked fine... I think I have to replace the MBR745 or maybe one of the other components.

    About the 3.3 for the Power good:
    I thought so too, but if you look at the sproggy MK2.6 PCB you will notice that the 5v has a lead that runs over to the power good circuit. and the 5/3.3v stands alone.
    Is this a flaw in the design?

    -Miles
    Near Completion: Intel P166 MMX, 32MB ram, 13GB Hard Drive, Keypad, 4x40 LCD. Sproggy MK2.6 ATX PSU. Win98SE with Winamp and Mark Zehnder Plugin. (Web-site: very soon)

  6. #6
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    Sep 2001
    Posts
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    Post

    Okay,I fixed it!

    It was one of the 2.7k Resistors that goes into the Vc line of the Max788 IC... I guess it was just a bad one, but it caused that whole side of my circuit to fail. Oh well

    BTW My Motherboard boots fine with the 5v Power good signal. I guess it doesn't really matter even if it is supposed to be 3.3v

    -Miles
    Near Completion: Intel P166 MMX, 32MB ram, 13GB Hard Drive, Keypad, 4x40 LCD. Sproggy MK2.6 ATX PSU. Win98SE with Winamp and Mark Zehnder Plugin. (Web-site: very soon)

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