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Thread: A4000TX ATX Amiga motherboard

  1. #301
    ChewChew's Avatar
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    Quote Originally Posted by Nrg View Post
    I bought MC68030FE33C
    I see from the pictures of the completed boards that 25Mhz 68030 have been used. If using a 33Mhz cpu, is it simply replacing the 50Mhz oscillator with a 66Mhz oscillator? Would you also need to replace the delay line (U102) to get nearer to the 8nS delay for the CLK90?

    Thanks in advance

  2. #302
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    looking at the Mouser BOM its about $250 USD

    Quote Originally Posted by pback View Post
    Quote Originally Posted by ChewChew View Post

    Hmm, you've got me worried. How much did the stuff from Mouser cost?
    I'm also interested in this.. anyone?
    - - - Updated - - -

    I tried it with a 66MHz oscillator and the board runs fine, however some of the zorro cards would not work correctly as the zorro bus is being over clocked.


    Quote Originally Posted by ChewChew View Post
    Quote Originally Posted by Nrg View Post
    I bought MC68030FE33C
    I see from the pictures of the completed boards that 25Mhz 68030 have been used. If using a 33Mhz cpu, is it simply replacing the 50Mhz oscillator with a 66Mhz oscillator? Would you also need to replace the delay line (U102) to get nearer to the 8nS delay for the CLK90?

    Thanks in advance

  3. #303
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    The Chips itself almost work without any issue because 33MHz was planned for later, but Fastram must have significantly faster timings that at 25MHz. Roughly calculated about 80ns / 33MHz * 25MHz i.e. 60ns for default settings and 80ns / 33MHz * 16MHz i.e. 40ns to be able to use Speedramsey
    The Delayline may or may not work without modding, the intended 25ns delayline has 5ns, 10ns, 15ns and 20ns taps (10ns i.e. 1/4 Clockcycle is used at 25MHz) but at 33MHz 7,5ns would be the right value...
    Also some ZIII cards have issues because they rely on the 25MHz ZIII timing even though the Bus works asynchronously without a fixed clock.
    In contrast ZII work flawless, because the timing is determined by the AA custom chip Clock.

  4. #304
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    Default A4000TX ATX PSUs

    Short follow-up to the earlier discussion in this thread about *new* ATX PSUs for Amiga A4000TX use.

    I went ahead and bough the smallest/cheapest model in the Corsair RMx (2018) series, as those are widely available at least here in Finland, and I could find proper looking reviews of those PSUs with measurements looking good. More importantly these PSUs seem to match the required minimum specs for A4000TX use (minimum required ratings: +5V @ 25A, +12V @ 10A, -12V @ 0,6A). There are other matching PSUs available aswell, but I couldn't find many which had proper reviews around with actual measurements included to verify the vendor claims.

    So anyway I bought the RM550x (2018) model (PN: CP-9020177-EU), which has ratings: +5V @ 25A, +12V @ 45A, -12V @ 0,8A. So far it has worked OK in my setup, which currently is A4000TX rev 1.1 with the onboard 030 CPU @ 25 MHz + FPU, and a ZZ9000 graphics card. I don't have a 060 turbo card yet.

    If someone else buys these PSUs there's one thing to note though: the specs say the ATX power cable is 20+4 pin, but it's actually 24-pin, so you might want to buy a separate ATX 24-pin to 20-pin adapter cable if you want the PSU connector to fit/lock nicely to the A4000TX motherboard (the default 24-pin connector works [with some force applied], but it's not "proper fit" because it's 24-pin / too big).

    Links to some reviews: https://www.tomshardware.com/reviews...pply,4484.html (earlier 2016 series, 550W), https://www.tomshardware.com/reviews...-psu,5568.html (2018 series, 850W) and https://www.kitguru.net/components/p...18-psu-review/ (2018 series, 850W).
    Last edited by Nrg; 1st November 2020 at 12:05.

  5. #305
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    Quote Originally Posted by screemo View Post
    @Hese: on the subject of the IO Shield - any good idea where to get this 3d printed, or even better getting an actual cut metal plate ?

    Edit: duh - just figured out you just select metal on one of them 3d print sites
    Do you have a link to a site I could use to print this? Would these I/O shield be printed or cnc cut?

  6. #306
    Retrocengo's Avatar
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    Amiga 4000 TX review on the way, i absolutely love this board����
    Little teaser video here:


    https://youtu.be/DooEpAG93Dw

    Hese, I’ve sent you pm

  7. #307
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    On the BOM there are Qty 7 of ATF16V8B-10JU and Qty 1 of ATF16V8C-5JX.

    I'm happy that the ATF16V8B-10JU are for both the 4 x GAL16V8-10 and 3 x GAL16V8-15, but I cannot work out what the ATF16V8C-5JX is for.

    Any ideas?

    Thanks

  8. #308
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    Hi

    Could you PM the cost of a fully populated board

    Many thanks

    Rich

  9. #309
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    A4000TX rev 1.1 PC Floppy Drive Fix
    There is a flaw in the rev 1.1 motherboard design when using a PC floppy drive (J300 jumper set to "PC" position). Thanks dorken for reporting the issue.

    When the J300 jumper is set to "PC" position, U356 pin 1 receives an incorrect voltage which may cause the chip not to function correctly. U356 is responsible for transmitting Amiga/PC specific floppy drive signals between the Amiga/PC floppy drive and the motherboard.

    The issue may occur only when the J300 is set to "PC". When using Amiga floppy drives (J300 set to "AMI"), the chip receives a correct voltage and this fix is not needed. I have used my motherboard with a PC floppy drive without the fix and haven't noticed a problem but your mileage may vary and it's recommended to do the fix if you are using the motherboard with a PC floppy drive.

    The issue can be fixed either by replacing one component on the motherboard (Method #1) or by rerouting the U356 pin 1 to another trace (Method #2).

    Method #1: Replacing a component
    The issue can be fixed by replacing the Q301 (2N3904) with a mosfet such as FDN357N. Mouser stocks FDN357N here. No other modification is needed.



    Method #2: Rerouting a trace
    The issue can be fixed by cutting the trace that goes to U356 pin 1 and connecting the U356 pin 1 to another trace with a jumper wire. No other modification is needed.

    This can done either on the top side (Method #2A) or on the bottom side (Method #2B). Do only one of these modifications.

    Method #2A: Doing the fix on the top side


    Cut the trace that goes to U356 pin 1 (marked with X in the picture). Solder a jumper wire between U356 pin 1 and R365 upper pad as show in the picture.

    Method #2B: Doing the fix on the bottom side


    Cut the trace (marked with X in the picture). Solder a jumper wire between the cut trace and J300 middle pin as shown in the pictures.


    Sorry for the inconvenience.

  10. #310
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    Hey Hese,

    If I apply fix 2A, does that affect the use of the jumper? Ie are locked in PC floppy only or can you still switch between Amiga or PC floppy drives.

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