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Thread: Superbrain QD repair

  1. #11
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    Oct 2016
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    Another vid - 7mins. Rambling through most of my test gear:



    I will do some actual testing soon!

  2. #12

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    It's OK Alan. I'm up to my neck in retro computers and my SB I and II both work, so I have no real cause for envy.

    You seen to be gathering tools. That IC tester looks a bit tasty... what's the plan? Will you use it to check all the logic chips on the board? If it's the one you sent me, I have a few ideas where you can start.

    That midi device looks like it connects to the SB serial port. I bet it is pretty simple inside. We could reverse engineer it!

    Regarding the Z80 ICE, I have already produced an 8080 ICE copy using a different board layout and a 3.3v CPLD. I'm planning to try to do the same with the Z80 ICE so you can possibly get your hands on one at some point.
    Last edited by JonB; January 27th, 2019 at 12:00 AM.

  3. #13
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    Hi Jon, I've just read through your stardot posts. Trouble is, if I gave you a video board - your various post might get a lot less interesting and convoluted! I never imagined such a lash up of old and new tech to be possible!

  4. #14
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    ....oh, my plan with the ABI chip tester, Id like to do some traditional fault diagnosis - my polar instruments device plus logic probes and schematics should help there. Once I get desperate enough and if I get no where doing it the proper way, will I then start desoldering chips one at a time to test them!

  5. #15
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    Last non - testing vid and last test kit vid. I'm only posting all this in case anyone has any guidance regarding my use of what I have in getting to a working Superbrain.


  6. #16

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    No need to give me one, I’ll pay you, or you might consider loaning me one.

    It’s either that or try to find a CRT monitor with enough deflection control to accommodate the SB’s horizontal overscan (which is excessive). It’s tricky enough finding s monochrome monitor..

  7. #17

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    Quote Originally Posted by alan8086 View Post
    Hi Jon, I've just read through your stardot posts. Trouble is, if I gave you a video board - your various post might get a lot less interesting and convoluted! I never imagined such a lash up of old and new tech to be possible!
    In fact, it is all old: the monitor guts came from an Amstrad GT65 (old green screen mono monitor supplied with the CPC464), the PSU is contemporary with my SB I (was used to provide 12v to the hard drive) and the sync mixer is made of LS7400 series ICs. The only thing that isn't old is the FDD emulator, and these devices are well known (jolly useful, too).

    I'm currently trying to guess how best to endow the GT65 with horizontal width adjustment. Errrmmmm.... not my area of expertise at all, but as long as I observe a few basic safety precautions I should be OK.

  8. #18

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    Well, I managed to hack the GT65 to show a narrower screen after all, with help from the guys at CPCWiki; so it looks like I'm OK monitor-wise for now. Offer still stands, though.

    But back to you, Alan: I'm waiting for the next update!

  9. #19
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    Oct 2016
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    Not much of an update - I've got my Suoerbrain spread out over that box I sent the board to you in:

    WP_20190129_14_32_58_Pro_LI.jpg

    I've burned one of the ROM dumps from one of your VCFED posts - a basic QD BIOS. Burned it on to a 2816 and the adapter board you supplied.

    I can count through the ROM part of the address map ok with my polar instruments device.
    It reports errors at every RAM address if you do the same on the RAM test - suggesting an issue with access to the RAM rather than every chip being faulty. Or maybe my device doesn't like Superbrains! The Learn test seems to create the address map ok - where ROM ends and RAM begins etc.

    The Shorts test says there is a short on address line 3 - I traced the route from adr3 pin on the Z80 from the schematics. I've logic probed/pulsed a nearby inverter and one other chip but found no issue with them.

    More probing to do and I'm wondering if it's worth de soldering all the RAM on both boards and testing it when my ABI tester arrives. I would have a pile of proven RAM that could be socketed back into the board. I would then 'only' have glue logic to worry about as I have good Z80s, working ROM and many of the socketed VLSI chips to substitute.
    Last edited by alan8086; January 29th, 2019 at 12:31 PM.

  10. #20
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    Oct 2016
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    Oh, I also lost the 15v going to the VDU board - now found it again. The 15v regulator leads got chopped where I managed to pinch them between the board and the case. I have good voltages going to the vdu driver board and a glowing crt heater. No HT but I suppose without any video signal I get no Horizontal or Vertical drive signal or anything to drive the flyback transformer?

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