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

  1. #11
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    Quote Originally Posted by cruff View Post
    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?
    I didnt. Just a visual inspection. I would assume an open joint if it was wonky or intermittent from the getgo. But it worked fine for 2 months.

  2. #12
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    Thanks Anthony, the second one looks to be the correct PCB even though the model number is not the same. Ill take a look.

    Quote Originally Posted by David_M View Post
    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.
    David I will check for an open per your instructions and post back. Thanks!

  3. #13
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    Quote Originally Posted by VERAULT View Post
    I didnt. Just a visual inspection. I would assume an open joint if it was wonky or intermittent from the getgo. But it worked fine for 2 months.
    Bad solder joints can sometimes be hard to find. If looking at that feedback transformer winding doesn't pan out, might be worth it to go back and reheat those joints. Also don't forget to look for leads you may have neglected to solder at all! That happened to me on a P112 board, I neglected to solder one lead of a resistor in the reset circuit. It worked initially then started acting up.

  4. #14
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    Quote Originally Posted by VERAULT View Post
    I didnt. Just a visual inspection. I would assume an open joint if it was wonky or intermittent from the getgo. But it worked fine for 2 months.
    Certainly my ii+ psu was fine when I got it, then occasionally flaked out, then got worse. If a joint is cracking, thermal cycling makes it worse, then an oxide layer builds up.

    Also, there was no way to see the cracked joint visually by eye. I worked it out by flexing the board slightly and seeing it spring to life. I can't remember why I diagnosed the transistor joint but after a quick solder, its been fine ever since.
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  5. #15
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    David I was getting 1.34 Ohms across R7. I decided to take the t1 (small) transformer out and check for shorts/opens anyway. The transformer is fine. I reflowed all my work. No change. I did notice that the leads were a bit to long on the c5 220uf cap and may have been grounding out on the chassis. I replaced that cap again. It occurred to me the fish paper sheet was missing. It may have deteriorated to dust. But its gone. If it was there I would have replaced it. Either way sound grounding may have occurred and I should have noticed, that's my fault.

    What else can I check?
    Last edited by VERAULT; May 30th, 2020 at 08:55 AM.

  6. #16
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    If its not ticking your problem will be on the high voltage side. Something is preventing the oscillations from starting, you said it was recapped so its not likely to be C5 so I'd be looking at the resistors particularly the low value ones. You will probably need to desolder and lift one leg of them to get good readings. In the past I've found R5 (120R) open but check them all.

  7. #17
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    have begun testing the high voltage side. Can someone tell me what exactly R1 is as its not making alot of sense to me: http://www.appleiioz.com/appleiioz/A...0schematic.pdf

  8. #18

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    Going by the schematic you point to, R1 NTC looks like it should be a NTC Thermistor, Basically it's there to protect the PSU from High inrush current at switch on, It should not be Open Circuit if it is your PSU will appear dead, Put your meter on Ohms reading and check, When they go they can be blown or open circuit. Obviously check with the PSU NOT powered.

    I have no experience with that PSU, Just going by the schematic.

  9. #19
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    Quote Originally Posted by VERAULT View Post
    have begun testing the high voltage side. Can someone tell me what exactly R1 is as its not making alot of sense to me: http://www.appleiioz.com/appleiioz/A...0schematic.pdf
    The schematic says that when R1 is cold (room temperature), it should read about 5 ohms. When it warms up after the power is applied, the resistance will drop.

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