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Thread: S u p e r b r a i n

  1. #21


    While I am wondering what to do with the blank screen, I thought I'd fix the Y keyswitch stem, which was broken off.

    First thing to do was to extract the remaining part of the stem from the inside of the Y key cap. Not easy. I ended up drilling a small hole dead centre, then winding a very small self tapping screw into it. This had just enough grip to allow me to pull the tiny + shaped piece of plastic out.

    Offering it up to the remainder of the switch stem, I was disappointed to find that it didn't match up properly, so there was no easy way to ensure that when it was glued together it would be straight and upright. However, I came up with a scheme.

    I found that the ENTER key (the red one from the numeric keypad) has three female receptacles to take the key stem (only one of which is used), and the outer two have the same spacing as two adjacent keyswitches. So I could use it as a sort of jig to hold the broken stem upright if I put the snapped off part into the left hand receptacle and fit the right hand receptacle to the key to the right of the broken switch. I put a little bit of epoxy glue on the switch plunger and fitted the ENTER key to the right hand key switch, pressing it down (not fully). I fitted some key caps around the enter key, taped a bar across the top (made of a piece of IC holder tubing) and stuffed foam in the gaps above and below the enter key. The purpose of all this is to ensure the broken stem stays square and in the centre of the plunger while the glue sets.

    The whole setup looks like this:


    It's a bit Heath Robinson, but it should work. Hopefully the stem will be strong enough by then to allow me to remove the ENTER keycap, then I can swap the switch to a position on the keyboard where it will be less used than Y.
    Last edited by JonB; April 11th, 2017 at 03:31 AM.

  2. #22


    Well, it didn't work at all. The stem was sort of fixed firmly, then got bashed accidentally, and came apart again. I tried with Superglue but no luck, so in the end acquired a spare switch from a BBC Master computer. These switches are made by SMC and are straight stemmed, type 4 linear. I now have a proper repair, and two spare switches.

    Meanwhile, I have been trying to trying to fix the mainboard and it's been a long effort that I documented over at StarDot:

    Head on over there for more news.

  3. #23


    And we're up!

    Well, sort of. I need a proper keyboard encoder (or the carrier board to be delivered by OSH Park!) and a suitable 8002 character ROM (-003 variant, with the 5x7 character set). Also, a new FD-1791 FDC, because right now it is running on a borrowed chip that came out of my TRS80 Model II. I also need a 50Hz CP/M boot disk so that the 60Hz mode does not get set when it boots.

    I seem to be getting close now!

  4. #24


    After a humongous effort, documented here and here, the Superbrain is working properly!

    Superbrain running.jpg

    Quite a few parts were replaced during this repair:-

    • Power supply rebuilt and recapped.
    • KR3600-PRO keyboard encoder carrier board and ROM to replace custom Intertec part.
    • FDC (floppy disk controller IC).
    • CRT8002-003 (video character generator IC).
    • All 32 4116 DRAM chips!
    • Sundry 7400 series logic ICs (about 10 of them, some unnecessarily).
    • The chassis fan (dead 115v noise maker replaced with a 12v quiet fan).

    Conspicuous by their absence are the two Z80s, the UARTs, the CRTC and PPI chips. For some reason these main ICs survived whatever catastrophe befell the machine (my guess: the blown out power supply).

    Along the way I implemented EagleTG and dmemphis's ROM reader and EEPROM carrier boards, although it turned out my TMS ROM was OK. Good thing too, as it carries the ACT hard drive's boot code! The hard drive itself is in unknown state. I managed to get the Superbrain to talk to it (meaning by that, issue head seek commands), but it won't read data at all, just times out. I will see if there is any data to be had from this drive; if not, I will attempt to reformat it. The ACT CBIOS code is, I believe, available on one of the Maslin images, so I should be able to SYSGEN it if need be.

    Next step? Implementation of uIDE Superbrain drivers, of course.

  5. #25
    Join Date
    Aug 2009
    Oslo, Norway
    Blog Entries


    Well done!

  6. #26


    I completed the "motor off" modification for Drive A so it stops spinning when not active, fitted a quiet fan (not that quiet actually - I'll have to go and buy another one) and spent quite a bit of time trying to get the drive and screen properly aligned in the Superbrain's front bezel. Not easy! Also, adjusted the monitor for a straight, sharp image.

    All it needs is (either) floppy drive B: or the MFM HDD repaired. Speaking of which, I'm not sure I can see the point of trying to fix it when I will have uIDE to play with. I suppose this means I need another Tandon drive to go in the B: drive bay...

  7. #27
    Join Date
    Nov 2017
    UK, South East


    Fascinating read - well done. I have have just acquired a Superbrain myself. It works -at least to a boot prompt but I don't have any fboot disks - have ordered some from retro system rescue.

    Mine is missing two keys - 2 & 3 from the top row. Interesting to read that you replaced one of yours from an old BBC - they are the wrong colour though ?

  8. #28


    I replaced key switches only, not the key tops, as I had those. SMC Type 4 vertical stems, came from a BBC Master, just to avoid confusion. The more common BBC Model B switches are different.


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