ACA 1233 55MHz

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  • Hi,

    I have bought ACA card from Sveta and I have problems with card being unstable.


    The warranty ID of the card is fTnr5.


    I have added RTC module from Amiga Kit to the card. It is brand new.


    My motherboard revision is:


    My PSU is:


    The motherboard has capacitors removed, according to http://wiki.icomp.de/wiki/ACA1…uired_board_modifications. It has been also recapped.


    The instability is expressing itself through bad access to the hard drive (I use CF card with the 2.5" adapter). For example when I run Alien2 demo by Scoopex, it hangs up after first part, where second executable should be loaded (it starts from bat script). Vertus demo by Potion also hangs in-between parts where loading of the data is required. After processor on the card gets warm after some 30 minutes of work I have experienced also hangs ups even in Workbench - it was either software failure with option to Suspend or Reboot or Guru Meditation. I have had once or twice Guru Meditation straight after powering the Amiga up.


    I have used this motherboard with GVP 1230 (Jaws II) @ 40MHz accelerator as well as with ACA 1233n @ 40MHz (newer model, (c) 2016).. When I bought my Amiga 1200 it came with GVP 1230 accelerator and Astec power supply, like that:


    But I have troubles, similar to that I have now with the ACA, but then it was even worse, for example video got corrupted like that. I have bought another Astec power supply, exactly the one above, soldered Amiga power connector and got even worse effect, instabilities straight away, disk indicating bad sectors. Finally I connected Commodore power supply from my Amiga 500 and got the Amiga stable on GVP. I have borrowed the ACA 1233n @ 40MHz from my friend and tried it with my Amiga. On Astec power supplies it had similar issues as GVP card, but with Commodore PSU everything worked stable. Now I have my own ACA 1233 @ 55MHz and it does not work work with Commodore PSU. I have another Commodore PSU, but this also does not work properly. Currently I have no access to Astec PSUs to test it out, but this would be the next step, I think.


    have also downloaded ACAtune and tried to disable burst, played with MAProm feature and few other options, but it did not changed anything. Surprisingly the card identifies itself as ACA1232, not 1233. Is that correct?


    I am 99% sure that the problem is within power supply here and I understand that 55MHz version will draw more power than 40MHz. I would be happy to invest into power supply that will be up to the job, but I don't know which one will be good here. Can I have some insights from wise people?

  • Hi,


    I confirm this card is from me (first owner) original buy from icomp shop and works here perfect on my A1200T rev. 2B and recap. Card is in original condition/state. (no FPU)


    Please Jens help lewizz where is problem/compatible issue. Thanks.


    Regards, Sveta

  • Those Astec PSUs have nice technical data, but you need to make sure that voltage drops on the cable and in the input coil are being compensated for. Measure the voltage of the 5V rail under load on the A1200 floppy power connector: It must be between 5.0 and 5.1V for the 55MHz card to work properly.


    We've found on the 55MHz ACA1233n that the card is a lot less sensitive to power supply ripple if the 55MHz oscillator gets it's own 12V->5V voltage regulator. See pictures of the mod in this post. Since the oscillator is exactly the same type between the ACA1233-55 and the ACA1233n-55, it will have the same sensitivity.

  • The original PSUs are perfectly suitable. All you need to do after all these years is to exchange the output capacitors.


    The reason why the old PSUs are so well-suited is that they have circuitry that adjusts the voltage according to load - similar to the sense wire technology that was introduced for the 3.3V rail of ATX PSUs.


    While most other PSUs are only suitable if connected to the A1200 with only a very short and thick cable (max. 20cm) and bypassing the input coil, the original Commodore PSUs are perfect without modification to the main board.


    Please note that not a single commercially available PSU for the Amiga uses any proper feedback loop for controlling the voltage.

  • OK,

    I have measured two Commodore PSUs I have my A1200 and ACA in. The one which works with GVP card gives in most cases 5.08V on 5V line of floppy connector. The other one gives 4.99V most of the time. There are some jumps in the voltage with the PSU giving 5.08V, but they are in a range of 5.05 to 5.10V only.


    So in your opinion recapping the PSU would sort out the problem?

  • I think I resolved the issue.


    Apparently it is caused by ROMs in my A1200. I have but ROMs from different Amiga 1200 and all works fine on all power supplies I have. I have put my ROMs in another A1200 and it fails with my ACA.