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Thread: 520ST power supply, NORTEL 70103-3

  1. #1

    Default 520ST power supply, NORTEL 70103-3

    Hi folks,

    Only 4 threads? Strewth.

    Anyway, after rediscovering my original 520ST with external power brick I cleaned it all up and hooked it up to a mono monitor from a MegaST4. It ran for long enough for me to start cleaning the heads on the SF354 floppy then I watched the screen flicker, fade and eventually die. Suspecting the monitor since it hadn't been powered up for $years I dug a similarly old SM124 out of the garage and got similar amounts of nothing. It wasn't till then I noticed the power light on the ST itself hadn't actually come back on so I switched over supplies from the floppy drive and the machine sprang into life again.

    I've managed to get the power brick apart and it's a nasty looking NORTEL board run by an NE5561. All the caps test ok with a DMM but seem to defeat my basic ESR meter, I suspect it can't deal with 4700uF caps.

    Is this worth repairing? It's a simple +5@3A and +12/-12@30ma brick and I've got an old Cisco PIX supply that fits the bill perfectly. I did plug it into the floppy drive and the motor spins so it's only the 5V rail that's gone but helpful stuff like schematics don't seem to exist online.

    Cheers! - UK home computer history
    Where RIFA capacitors come to die

  2. #2


    aaaand then I find a thread from July last year with someone asking a similar question, I guess those threads got archived when the hosting switched... - UK home computer history
    Where RIFA capacitors come to die

  3. #3
    Join Date
    May 2009
    Blog Entries


    The default forum listing only shows threads from the last two months. Go to the bottom of the forum listing and there will be a selection to "show threads from the..." and set that to Beginning which will give you all the threads back to 2003.

  4. #4


    Idk, I have a 520ST, got it free just had to pay for everything else, and used one of those alternate power bricks like the Cisco, was easy enough for me to not bother with an original... Course if you could fit a Cisco in the original case that'd be cool...

  5. #5


    I thought about that The triple output supply mentioned in your other thread would definitely fit though, but I don't use that particular ST enough (or indeed at all really) to warrant a 25 spend.

    W - UK home computer history
    Where RIFA capacitors come to die


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