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Thread: So these 3 Superbrains followed me home...

  1. #11

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    You should ask someone to send you one...

  2. #12
    Join Date
    Oct 2016
    Location
    Burnley, UK
    Posts
    303

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    Quote Originally Posted by Witchy View Post

    I did also try and buy a replacement 10uF 35V bipolar cap but like Jon I ended up with a couple of tiny ones.

    Cheers!
    This is what I use as a replacement for the non polar electrolytic cap...

    10uF non polarised cap for Video Output board.JPG

    You'll have to click on the thumbnail - snip was too small.

    I got 5 off eBay a year or so ago - my SB display has been fine and the component itself seems to have enough current throughput so that it doesn't overheat like those tiny modern electrolytics do.

    Regarding your blown BU406 - one of my video boards had the same issue. The 15pF cap directly behind BU406's heatsink had gone short circuit - marked C438 in this board:

    SuperBrain video board C438 compressed.jpg

    The one in the pic is a modern replacement - the original was a smaller green plastic axial tube thing, had hard black sludge leaking from one end. Once I replaced it and the BU406, I had a picture - which rapidly shrank in width as smoke poured from that aforementioned non polar electrolytic. Once that was replaced, I had a great SB display!

  3. #13

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    Quote Originally Posted by alan8086
    This is what I use as a replacement for the non polar electrolytic cap...


    Ah yes! I didn't think of those, I'll have a search through my spares bins to see if I've got anything suitable. Nice one!
    www.binarydinosaurs.co.uk - UK home computer history
    Where RIFA capacitors come to die
    facebook.com/binarydinosaurs

  4. #14

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    I pulled one from another monitor. Not terribly good practice I know, but the screen is working now. You can also make one up by putting two normally polarised caps back to back (that is + to - / - to + if you get my drift) though I haven't tried it myself.

  5. #15

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    Bah. Replaced the BU406, CR412 and put the ok-but-seemingly-far-too-much-overrated bipolar cap back in and I still get a scream. Fortunately the components I replaced are still OK so the fault obviously lies elsewhere...but where.

    Wait, what's this? 22uF 50V Capacitor on a wonk in the HV circuit path. Let's just pull that out...

    IMG_9504.jpg

    The Screaming Cap! The one next to it (470uF 25V) also tests low with high ESR so we'll swap that one too. Suddenly...

    IMG_9506.jpg

    Picture is a bit wobbly on the horizontal as it is with its original analogue board - the one currently in is from the SB1.

    So! That's 2 almost-fully working SB2s and a supposedly working SB1 but at least the SB1's CRT tray is fully functional now. Just need to sort out its lumpy capacitored PSU! Oh, and work out how to put it back together
    www.binarydinosaurs.co.uk - UK home computer history
    Where RIFA capacitors come to die
    facebook.com/binarydinosaurs

  6. #16

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    Well done Witchy!

    Now you just need a copy of the proper boot disk for this machine (which doesn't leave the screen in reverse video). I have it - so if you PM me your address you might get a nice pre-Xmas present. Oh, and I'll stick the uIDE SB II utility suite on there as well. You never know

    Also have it as an image file if you can stick it on a disk.
    Last edited by JonB; November 21st, 2020 at 09:11 AM.

  7. #17

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    Funnily enough I'm just having a go at writing some disks as we speak, namely the SB II Boot one plus a couple from Don Maslin's archive. Not having much success but I suspect head incompatibility between the writing drive in my floppy imaging PC and the SB's. Since the drive from the SB1 is currently loose I'll try hooking that up to the PC and see where we go. I've actually got another drive out of a Superbrain that I can't remember the origin of (to me, obviously its ultimate origin was a Superbrain) so I'll see if I can find that too.

    Settings I'm using: 40 track, single sided, double step off. Disk is unreadable in a real machine or in 22disk with SUP3 as the definition.
    www.binarydinosaurs.co.uk - UK home computer history
    Where RIFA capacitors come to die
    facebook.com/binarydinosaurs

  8. #18

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    Quote Originally Posted by Witchy View Post
    Funnily enough I'm just having a go at writing some disks as we speak, namely the SB II Boot one plus a couple from Don Maslin's archive. Not having much success but I suspect head incompatibility between the writing drive in my floppy imaging PC and the SB's. Since the drive from the SB1 is currently loose I'll try hooking that up to the PC and see where we go. I've actually got another drive out of a Superbrain that I can't remember the origin of (to me, obviously its ultimate origin was a Superbrain) so I'll see if I can find that too.

    Settings I'm using: 40 track, single sided, double step off. Disk is unreadable in a real machine or in 22disk with SUP3 as the definition.

    I have a GoTek on my SB II board as no working TM100 drive units.

    AFAIK the only SBII boot disk in the Maslin archive boots to reverse screen. Zippysticks and I had to hack a working disk together, then when I reverse engineered the hidden BIOS I found where it sets the video chip up and fixed it properly. Thatís why Iím offering to send you a disk.

    I think you need double step on.

  9. #19
    Join Date
    Oct 2007
    Location
    United Kingdom
    Posts
    298

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    Good work Witchy, glad you got your screen back, I must find the time to dig out the screecher, and checkout the caps , I originally thought the flyback was needing replacing, but your findings now give me new hope! thanks for sharing.


    harry

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