ACA500Plus startup

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Don't Panic. Please wash hands.
  • I just received my ACA500Plus, to use on the following setup - PAL Amiga 500+, 1Mb Chip, high-end (5.5A on 5V) new power supply. ACA updated to latest firmware.


    Have to say, a very impressive product, so much more than just an accelerator, the WB install is awesome, the profiles work great, etc. With that said, I have two issues, a small one and an annoying one:


    #1 - when I first start the machine cold - the ACA display does the spin, then shows 00, then FF, screen goes dark blue, and nothing happens. Now if I reset with Ctrl-A-A, I get the menu, and everything works great. If I use it for a bit, I can turn off power and turn it back on, and the menu shows up.


    #2 - the floppy drive, which works perfectly fine without ACA attached (tested over many reboots, with many disks), has a mind of it's own. On one boot, it will read all disks no issues. The very next boot, it might start throwing errors here and there, but a Retry fixes it. Then once in a while, it won't read any disk, until I reboot.


    Any ideas?

  • high-end (5.5A on 5V) new power supply.

    Please link to the source of that PSU - never seen a proper one with those specs.


    #1 - when I first start the machine cold - the ACA display does the spin, then shows 00, then FF, screen goes dark blue, and nothing happens. Now if I reset with Ctrl-A-A, I get the menu, and everything works great. If I use it for a bit, I can turn off power and turn it back on, and the menu shows up.

    That's a known issue with A500 computers that have an ageing timing-capacitor in the NE555 reset circuit. I have a number of those A500s too, and I learned to live with the startup-keyboard-reset requirement. I'm just too lazy to exchange the cap on the A500. Sometimes it helps if you put a 1k pullup resistor on the reset signal, but the root cause is the cap.

    #2 - the floppy drive, which works perfectly fine without ACA attached (tested over many reboots, with many disks), has a mind of it's own. On one boot, it will read all disks no issues. The very next boot, it might start throwing errors here and there, but a Retry fixes it. Then once in a while, it won't read any disk, until I reboot.

    Sounds like a power supply problem. Again, please mention the exact type of PSU, so I can look at the specs.

  • Please link to the source of that PSU - never seen a proper one with those specs.

    It's made by Ray Carlsen, a well-known and respected Commodore resource in the US:


    https://portcommodore.com/rcarlsen/customPS.html


    It's the $70 one down the page.

    That's a known issue with A500 computers that have an ageing timing-capacitor in the NE555 reset circuit. I have a number of those A500s too, and I learned to live with the startup-keyboard-reset requirement. I'm just too lazy to exchange the cap on the A500. Sometimes it helps if you put a 1k pullup resistor on the reset signal, but the root cause is the cap.

    Got it!

    Sounds like a power supply problem. Again, please mention the exact type of PSU, so I can look at the specs.

    I've used this PS with a loaded 1200 with no issues, unfortunately the only other supply I have at the moment is a stock 1200 one, which I keep away from my 500.


    I will get my hands on a different PS just to eliminate this as a possibility.

  • It's made by Ray Carlsen, a well-known and respected Commodore resource in the US:

    Definitely respected as a person, but not as an engineer for power supplies. The unit is not available as 230V unit, so I have a hard time to test it, but if you open it up and snap a picture of the internals, I'm happy to give you some detailed comments, based on the original Commodore specification.

  • That's a known issue with A500 computers that have an ageing timing-capacitor in the NE555 reset circuit. I have a number of those A500s too, and I learned to live with the startup-keyboard-reset requirement. I'm just too lazy to exchange the cap on the A500. Sometimes it helps if you put a 1k pullup resistor on the reset signal, but the root cause is the cap.

    Aha. I used to have the bluescreen issue at coldboot with my regular ACA500 quite a few years ago. Not seen the issue in quite a few years. And not seen it with my ACA 500 Plus either. Probably because I have recapped all my Amiga 500 motherboards. And I hadn't recapped them at the time I had the issue. I assume the capacitator that causes this issue is the 10uF one close to the 555 timer. Appart from that I'm only using recapped original Commodore PSUs.

  • Definitely respected as a person, but not as an engineer for power supplies. The unit is not available as 230V unit, so I have a hard time to test it, but if you open it up and snap a picture of the internals, I'm happy to give you some detailed comments, based on the original Commodore specification.


    The actual power supply used in the enclosure is a Mean Well PT-65-R17VA, which is rated at 5.5A and 50mV ripple at 5V.


    I have also tested my 500+ an ACA500+ with my original 1200 power supply (the 3A version) and it shows the same behavior. Otherwise both are stable with no issues running over several hours and working the board hard.

  • Mean Well PT-65-R17VA

    That's known-bad for use on a distant power sink. It only regulates voltage at it's own output, but does not know or care about the voltage drop on the cable, which varies based on the load. I wonder why I have to repeat this over and over again: Do not look at the specs of the chassis, but the complete system you're building. Do you NOW understand why I mentioned that there is no engineering whatsoever if you ignore simple technical facts?


    Anyway, the 10µF cap near the NE555 is what you should be looking at; it's the most likely source of the inconvenience.

  • That's known-bad for use on a distant power sink. It only regulates voltage at it's own output, but does not know or care about the voltage drop on the cable, which varies based on the load. I wonder why I have to repeat this over and over again: Do not look at the specs of the chassis, but the complete system you're building. Do you NOW understand why I mentioned that there is no engineering whatsoever if you ignore simple technical facts?


    Anyway, the 10µF cap near the NE555 is what you should be looking at; it's the most likely source of the inconvenience.


    My apologies, I am just a stupid customer. Can you please cancel my order #111729. Thanks.

  • My apologies, I am just a stupid customer.

    My apologies if this came across as if I would be criticizing your "engineering" - the criticism goes to Ray Carlsen, of course.


    I'll eMail you about cancelling the order - I need at least an eMail, not a forum post.

  • Anyway, the 10µF cap near the NE555 is what you should be looking at; it's the most likely source of the inconvenience.

    OK, finally got my A500 apart and replaced the cap (C712). Unfortunately it did not change the behavior. It's not a big deal, but since I have it apart, please let me know if you have any other suggestions I could try. Thanks!

  • You could try adding a pull-up resistor of 1k ohms between the reset signal and the 5V rail. This can be put to many places on the board, or even on the ACA500plus itself. Let me know if you need help identifying possible points.

  • You could try adding a pull-up resistor of 1k ohms between the reset signal and the 5V rail. This can be put to many places on the board, or even on the ACA500plus itself. Let me know if you need help identifying possible points.

    That did it, thanks!

  • The easiest way, if you do not have an X-Surf-500 yet, is to insert the resistor into the X-Surf-500 expansion port of the ACA500 or ACA500plus (connector has the same pinout). That would look like this:

    This picture shows an ACA500, so it'll look slightly different on the ACA500plus. The mount hole is in the same position, so orientation should be no problem.


    If this solves your startup problem, you can choose pretty much any spot between reset and 5V in the computer, freeing the expansion connector again. Check A500 schematics for possible points - they are different for different board revisions, of course.

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