ACA500+ Green Screen

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Don't Panic. Please wash hands.
  • Does anyone know what this green screen means? I have only just recently purchased my ACA500plus and I have installed it into my A500+. It works fine at 14 and 21MHz, but displays this screen when I boot my CF card at either 28 or 42MHz.


    I have an older Rev5 (I think) A500, which works fine at any speed, but obviously doesn't benefit from the ECS or additional RAM of the A500+.

  • This green screen is the ACA500plus's internal exception handler. It means that your card cannot work at 28 or 42MHz. Good to hear that it does work fine at 21MHz, as that's the guaranteed speed.


    Try a better power supply, this might give you better overclocking results. However, don't fall into the "I'll buy a new PSU"-trap, as the PSUs that are currently on the market are either under-powered or based on a MeanWell chassis, which is not suitable for an Amiga.

  • Hi Jens, thanks for the reply.


    I was not sure if it was something to do with my Amiga A500+ or the ACA500, as it works fine at 42MHz in my older A500.


    I probably won't run it at those speeds anyway, I just wanted to make sure it wasn't a problem with the accelerator as I would like to try an A1200 card with it at some point (thank you for your email earlier).


    When you say "try a better power supply", what do you mean? I only have original Commodore PSU's. Why would the power supply be the issue?

  • Why would the power supply be the issue?

    When expanding the Amiga, the expansions will require more power. More power means that the voltage drop on the cable and in the input coil of the A500 will rise, so the usable voltage inside the computer drops.


    If the ACA500plus is working fine on the older A500, but not on the A500+, I assume that you have two separate power supplies for them that have aged differently, as the power consumption of A500 and A500+ is not substantially different.


    A switch mode power supply has the additional problem that with higher load, the ripple voltage goes up, which will reduce your chances for overclocking success. With high-enough ripple and enough voltage drop, you start to see parts of the Amiga fail - first it's overclocking that does not work, then you get random read/write errors and at some point, the keyboard controller will fail it's self-test and blink the caps LED.


    I'm working on a PSU replacement that addresses all these problems with a cable drop comensation circuit: While you see the voltage at the Amiga drop down to less than 4.8V if loaded at the rated load of 3A with the old Commodore PSUs, my PSU will provide a rock-solid 5.0V up to a constant load of 5A, and it can even provide a short-term current of 6.5A. Even at that short-term load, the ripple voltage is in the range of 40mV.

  • If the ACA500plus is working fine on the older A500, but not on the A500+, I assume that you have two separate power supplies for them that have aged differently, as the power consumption of A500 and A500+ is not substantially different.

    Hi Jens, that makes sense now. But I used the same power supply for both my A500 and A500+

  • But I used the same power supply for both my A500 and A500+

    Maybe there's an expansion inside the A500+ that consumes extra power? Maybe additional disk drives connected? Gotek drive? Anything that consumes power can be a cause for malfunction if you don't have cable drop compensation, and so far, I haven't found any of the original PSUs (and definitely not the newly-available ones) that have such a compensation.

  • with a ROM switcher

    So there's an expansion after all :-)


    Maybe it's not voltage, but ripple - the A500+ might have lower total capacitance, so there's higher ripple on the 5V rail. Since you have found that the ACA500plus is overclocking nicely on the older A500, it's really a matter of guessing, maybe even a matter of temperature for the PSU. There's no way to say that (even from a distance) unless you can measure the exact voltage and ripple in both systems. Please try to use a different PSU if you have one.