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Thread: IIGS Astec AA13581 repaired 2 months ago went bust. Need help

  1. #1
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    Default IIGS Astec AA13581 repaired 2 months ago went bust. Need help

    I had an Apple IIgs psu model Astec AA13581 psu that was in really sad shape a couple months back. Dirty and probably saw some water damage. I replaced all the Electrolytics and AC safety caps and it has worked great for 2 months until last night. IT started giving intermittent issues that presented like power switch problems (it would turn on and off for a split second by rocking the switch.. Then dead.) I tried a brand new switch as that is what it seemed but the first switch was fine and the new switch made no change.

    I am getting NO voltages out of this thing on any of the pins. Could use some help checking the obvious. Anyone have a schematic or guide on this type? Oh yeah, fuse is fine.

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    While it was an Apple II psu, I had a very similar problem which was due to a cracked solder joint on the big power transistor and it would refuse to start. Might be worth a quick trip around the board ?
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    Quote Originally Posted by Gary C View Post
    While it was an Apple II psu, I had a very similar problem which was due to a cracked solder joint on the big power transistor and it would refuse to start. Might be worth a quick trip around the board ?
    I was in the same mindset. I was checking for bad joints and nothing obvious jumped out at me.

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    Are there any Sam computer facts or anything that late in the game for troubleshooting these psus? Anyone have a schematic?

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    If it isn't blowing the fuse, then maybe it is shutting down due to an overvoltage or overcurrent regulation. Does it shutdown if you don't have any cards in the slots? Do you have an oscilloscope with a differential probe?

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    Found this Apple document for older switched power supplies, it has good information about switched mode power supply circuits, but won't answer your questions directly. http://bitsavers.org/pdf/apple/power...lies_Aug82.pdf

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    Quote Originally Posted by cruff View Post
    If it isn't blowing the fuse, then maybe it is shutting down due to an overvoltage or overcurrent regulation. Does it shutdown if you don't have any cards in the slots? Do you have an oscilloscope with a differential probe?
    you can test the voltages when the psu is out of the system on its own. I have an identical psu (exact same pcb) I tested this with. You get two gorund pins, a 5v a 12v a -5v and a -12v. With this psu you get nada.

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    Quote Originally Posted by VERAULT View Post
    you can test the voltages when the psu is out of the system on its own. I have an identical psu (exact same pcb) I tested this with. You get two gorund pins, a 5v a 12v a -5v and a -12v. With this psu you get nada.
    That makes it easier for testing at least you don't have to put a load on it to behave. Unfortunately in my IIgs I have a power supply made by DynaComp, so I can't go about looking to reverse engineer it to get you the information you'll probably need. Did you reheat the solder joints for the parts you replaced, just in case one of those went open?

  9. #9

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    Quote Originally Posted by VERAULT View Post
    I had an Apple IIgs psu model Astec AA13581 psu that was in really sad shape a couple months back. Dirty and probably saw some water damage. I replaced all the Electrolytics and AC safety caps and it has worked great for 2 months until last night. IT started giving intermittent issues that presented like power switch problems (it would turn on and off for a split second by rocking the switch.. Then dead.) I tried a brand new switch as that is what it seemed but the first switch was fine and the new switch made no change.

    I am getting NO voltages out of this thing on any of the pins. Could use some help checking the obvious. Anyone have a schematic or guide on this type? Oh yeah, fuse is fine.
    http://www.appleiioz.com/appleiioz/A...t_Diagram.html

    Maybe? No, this one...

    http://www.appleiioz.com/appleiioz/A...t_Diagram.html
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    Since it has been recapped already, your problem is most likely the little feedback transformer. One of the windings goes open circuit, I see it mostly in 2+ and 2e power supplies.
    The quick way to check is is measure the resistance across R7 (56R), if you read 56 ohms or close to it then the winding has gone open.
    You can replace it with one from a donor supply or do what I do and wind about 30-35 new turns of enameled copper over the top of the old winding.

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