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  1. Important Information

    1. The 68kMLA Forum Rules   (10141 visits to this link)

      To quote vintage Apple manuals: "Read Me First!"

  2. Community Connections

    1. General 68kMLA News & Stuff

      What's going down in the barracks.

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    2. Conquests

      Discuss your latest vintage Mac finds!

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    3. Trading Post

      Feel free to trade all of your Mac goodies here with all honest intentions. The website provider assumes NO liability, so buyer beware! Please see this topic for more information.

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  3. Projects & Hosted Forums

    1. RetroChallenge

      What can you do given only one month and strictly "retro" hardware? Find out with RetroChallenge!
      http://retrochallenge.org/

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    2. 68kMLA Wiki

      The creation and maintenance of the 68kMLA's information repository.
      http://68kmla.org/wiki/

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  4. 68k Model Forums

    1. Compact Mac

      Macintosh, 512k, SE, etc.

      46023
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    2. Mac II, Quadra & Centris

      Just think, having a Quadra 950 in 1992 would be like having a Mac Pro today… except with more slots, more expandability, and on-board SCSI!

      13113
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    3. 68k LC & Performa

      Ah, the consumer computers!

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    4. 68k PowerBook

      From the Portable to the 190cs.

      9875
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  5. PowerPC Model Forums

    1. NuBus Power Mac, LC & Performa

      The NuBus architecture gets a new brain!

      2672
      posts
    2. PCI Power Mac & Performa

      The PPC comes of age and adopts the industry standard expansion slot.

      5881
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    3. G3/G4/G5 Power Mac, iMac & eMac

      From the Beige G3 to the quad-core G5, via various iMacs!

      13747
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    4. PPC PowerBook & iBook

      All that power in a laptop? Never…

      8970
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  6. Everything Else…

    1. Apple I, ][, /// & Lisa

      Not really 68k Macs, but certainly Vintage!

      7398
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    2. Newton

      The best PDA ever finally gets its own forum!

      1066
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    3. Software

      Includes system stuff, productivity, emulation, design, and games for pre-OS X Macs!

      17464
      posts
    4. Hacks & Development

      Yes, it's back! Hardware hacks/modifications and software development for Mac OS.

      18630
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    5. Peripherals

      Anything you can hook up to your Mac or stuff into it as an interface!

      14548
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  • Posts

    • Yes! It’s always good to see something come back to life. Well sleuthed!
    • Wading through just about anything to get just a little bit of something hidden therein ain't relaxing. I like to leisurely watch your videos, maybe with a cold glass of lemonade in hand. They're much appreciated by all here I think and thanks much!  
    • Mystery solved! Found an old post that mentioned the 280c logic board has 4 x 35v 100uf (check), 1 x 35v 47uf (check), 1 x 25v 33uf (check), and 1 x 25v 100uf (eureka!). I had all of the above in my parts bins, so recap complete.

      My new friend gave me a bit of a scare today after buttoning it up though: Hung on the initial gray screen, even after numerous power-cycles. From my research trying to track down that cap value, I read numerous horror stories about leaking caps causing exactly that behavior on Duos 

      Gravely concerned at this point, I opened it back up and started poking around with the DMM and scope. I couldn't find a schematic anywhere and the board is a forest of vias (who knows how many layers...), but while probing around in the DC-DC circuitry, I noticed that "DZ6" was open!  D = diode, Z = Zener I assumed. The little SOT-23 SMD had "8Y" silked across the top, and a bit of googling suggested an SOT-23 packaged Zener diode thusly marked was perhaps an MMBZ5248? That I certainly didn't have, but I contacted a tech I'm friendly with at a local electronics repair shop and he did  Booted right up after replacement. A $0.13 part almost ruined my day.

      This particular failure mode was probably specific to my board, but if any of you are hanging on to failed Duo boards, replacing DZ6 might be worth a shot...
       
    • I do this with my Macs - it prevents it coming loose when you transit the Mac, the video board socket doesn't hold onto the CRT's neck too well on its own from my experience.   Have you checked continuity from the brightness knob on the analog board?
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