ACA500PLUS [ERROR 20]

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Don't Panic. Please wash hands.

    Hi !


    Recently I order to a friend an ACA500Plus

    It work good on 2 of my Amiga500, no error. (great product) :thumbup:


    But, on another amiga, Amiga500 PCB REV8 (so Amiga500Plus with 1Mega chip ram)

    Don't working;(


    I have, in order to my screen on amiga boot :

    - Black screen

    - Blue Screen

    - Purple Screen

    - return to BLUE screen

    - and finaly, stuck to Black screen


    Print 20 on 'LED DIGIT' (and led Green bright)

    And exactly, on boot, on this Led digit ==> (turn digit) --> 0 --> 5 --> 6 --> 20



    This Amiga500+ passed with succes All diagrom Test (and logical rom)

    I have 2.05 kickstart ont it, it seams working good on all tested games and demos

    But... maybe it has an H/W issue ?


    Can you tell me the signification of the number printed on the 'mini led panel' of aca500 ?

    So 0, 5, 6 and 20


    I have alread repair this amiga (20 wraps) around DATA PATH
    Tested all lines of CIA(A & B), PAULA, GARY and ROM

    But... maybe there is still something wrong.

    Knowing what the numbers displayed correspond to would help me.


    Thks a lot

    The numbers that are displayed on the DisMo are for internal debugging only - they may change from version to version, so documenting them makes no sense. You get much more information when using a terminal: Connect the ACA500plus to a known-good A500, go to global menu, activate serial debugging and use a nullmodem cable to see clear-text messages. If I remember right, it's 115200 Baud, 8N1.


    Kickstart makes no difference. You can even remove the ROM from it's socket and run the computer with just the ACA500plus connected. Kickstart comes from Flash in all cases - only if you specifically choose the physical ROM chip, it will be used, but otherwise, the original versions from flash will be used.


    First thing I'd look at would be the power supply - is that the same as the one you have been using successfully with the other two A500 boards?


    Next, the ACA500plus is very sensitive to reset glitches. These occur if the electrolytic capacitor in the reset circuit of the A500 has dried out. However, the DisMo usually stops at FF in that case, and you can resolve it by doing a keyboard reset. Still worth a try, as it may crash in different places.

    Hi !

    Serial Port activated with another A500 as you said, and I have this.


    I have tested 3 powers supply without change.
    And ofcourse, alim that have use with this 500+ have been tested well with another amiga.


    >These occur if the electrolytic capacitor in the reset circuit of the A500 has dried out.

    In this case, (wrong of not 'clean' reset_signal, I should have problems to boot with the amiga without the aca500 ? it's not the case.
    I can take a look with osciloscope to the reset_signal and, in doubt, I can change too the capacitors.

    C42, C711 and C713, I don't think so, but I can desolder and mesure them.
    C712... maybe.... To check.

    I already test the 'keyboard reset', don't change this problem.
    Amiga reboot, and I can see finaly '20' on the digit.

    Quote from Giants

    In this case, (wrong of not 'clean' reset_signal, I should have problems to boot with the amiga without the aca500 ? it's not the case.

    The older 8MHz HMOS CPUs are more forgiving in terms of the reset signal, so there is a difference between using the ACA500plus or not.


    Quote from Giants

    I already test the 'keyboard reset', don't change this problem.

    Like I wrote, it *should* stop at FF if reset is the cause, and if keyboard reset doesn't change anything, the reset circuit is most likely not the culprit.


    Since this is only happening on a single A500+ board (which probably had a leaked battery in it's previous life), I'd go to de-brick mode and run very simple monitor software first, see if the machine is really 100% usable: Test memory, see if chip ram is fully usable.

    >Since this is only happening on a single A500+ board (which probably had a leaked battery in it's previous life), I'd go to de-brick mode and run very simple monitor software first, see if the machine is really 100% usable: Test memory, see if chip ram is fully usable.

    Yep, already done by testing all hardware in this PCB with

    - Diagrom 1.2.1

    - Logica-dialoga-200
    - Amiga Test Kit by keirf.


    All tests passed by success.

    That's why I find it strange., if they are problem on this board (and I think they are a problem on it).

    Why in 'normal mode' (Gaming, play demo), all working good... that's... strange isn't it ?
    Ah, PiStorm don't work on this board (black screen)
    It goes back to the fact that there is undoubtedly a hardware problem somewhere on this PCB.

    But where...


    C712 replaced : No change.

    I don't already tested all line of CPU, I going to do this.

    Just got an answer from Toni, the author of the ACA500plus software. This may be a problem with chip ram access, as it's close to "testing what CPU is active" and "change/restore exception vectors". Remember that the DisMo codes are not like PC-world-POST codes, as no actual testing is performed. It's just a simple way of sending a debug message, which is not really meant for the user.


    That said, if chip ram access fails, you'll find out if you go to de-brick mode (hold DisMo button until you see "0_" blinking) and then do a keyboard reset. This will run the CPU on the ACA500plus, but not execute the ACA500plus ROM, but the A500's Kickstart ROM. Make this work first - if chip ram is really the problem, it may be as simple as cleaning the 86-pin port of the A500+ with alcohol and micro fibre cloth. Do not use contact sprays, as these usually contain extra lubricants that you don't want on a computer connector.

    Quote from Giants

    Yep, already done by testing all hardware in this PCB with

    - Diagrom 1.2.1

    - Logica-dialoga-200
    - Amiga Test Kit by keirf.

    Was that really with the ACA500plus in de-brick mode? Or did you remove the ACA500plus for that?


    I'm specifically talking about the ACA500plus attached, but put into de-brick mode. This will disable the 68000 on the A500 and still use a lot of the ACA500plus hardware.

    de-brick mode ? What's that ? Button pressed on Aca500+ ?
    I already test that, I have a red fluctuating screen.


    All tests with (Diagrom, logica, AmigaTestKit) have been passed without Aca500+ connected ofcourse.


    I just tested another card on this Board (A500+ Rev8 - 1Mb Chip + clock)

    - Aca500+ (so don't working - Error 20)

    - MKIII (don't working, strange color in screen)

    - PiStorm for replace the CPU and so, nothing else connected. (don't working, black screen) (tested with Kickstart 1.3, 2.05 and 3.1)


    All my Cards has been tested well on other Amiga ofcourse.

    Aca500+ working

    MKIII working

    PiStorm working

    They are, somewhere on this Rev8, a hardware problem, for sure.

    Only* Aca500+ have a serial port who can help me with this problem.

    Diagrom has it too but... doesn't give any problems...

    So like I suspected from the very first post in this thread, this is turning out to be an A500 mainboard repair thread.

    Quote from Giants

    de-brick mode ? What's that ? Button pressed on Aca500+ ?
    I already test that, I have a red fluctuating screen.

    Red? That's usually the colour you see if the Kickstart checksum is not correct, and that's only the case for 512k Kickstarts. So yes, there is something wrong with the path between ACA500plus and the main board. You might want to double-check if there are scratches on the board that interrupt traces.


    Let's go for the very simple things first: Is this a "real" A500+ with RTC on-board and 1MB chip ram assembled on the main board, or is it "just" a Rev.8 board with 512k chip ram and no RTC? That makes a huge difference in terms of "possibly leaked battery", and possible expansions that a previous owner has installed (which are now removed, of course).

    Yes and No :)
    Yes because it's NOT a issue with Aca500+ for sure.

    No because, I know it's Not an Aca500+ issue but I wanted to know what the value 20 corresponds to.

    And your answer to activate the debud mode of the serial port was a good idea.

    Now, I know exactly the right sequence (with serial) of ACA500+_booting and I know the bad sequence also.

    Based on this logs, I think it's a line problem on the CPU.


    >Red...
    Yes, by repair experience, the color issue on amiga is often misleading.

    I know it's not the kickstart himself, but as you said, probably a problem with a cut or damaged line.

    It's because I would like to know exactly the value 20 corresponds, to conduct my research. ;)


    It's a Real Amiga500+ so with all chipset solder on it.
    RTC and co.

    Yes of course, there was leaked battery on it.
    I have repaired more than 20 cut lines, always around DATA PATH & GARY


    I already check all lines of :
    - GARY
    - DATA PATH CHIPSEST
    - KICKSTART
    - CIA (A) & (B)
    - PAULA


    Yesterday I started to check the lines at the CPU and so, Agnus.

    The road is long :)
    I already check with no error find Half line of Cpu.


    I have ordered yesterday a re-Amiga500+

    If I don't find issue on this Board, I would do the transplant.

  • The last reply was more than 365 days ago, this thread is most likely obsolete. It is recommended to create a new thread instead.

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