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Thread: Amiga 500 Gray -> Yellow screen at power-up

  1. #1
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    Default Amiga 500 Gray -> Yellow screen at power-up

    My Amiga 500 has stopped working. On power-up, I get a brief gray screen and then a yellow screen. The power LED flashes 10 times and then the system reboots. (This goes on continually.)

    Looking online, people say to remove the RAM expansion card. Sadly removing the 512k Supra RAM+Clock card doesn't change anything. (In case you were wondering, this card uses a CR2032 so has no leakage.)

    I have also:
    - Swapped the CPU
    - Swapped the Odd <-> Even CIA chips
    - Swapped Agnus for another chip
    - Tried a different (known good) power supply
    - Reseated all the custom ICs

    No change with any of these. My Kickstart 2.0 ROM has a jumper wire from one pin to another -- removing it ends up in a RED screen (which maps to bad ROM) but restoring the jumper results in the yellow screen again.

    Video of the problem happening -> https://www.youtube.com/watch?v=O5feotX9Iz4

    Any Amiga experts have any suggestions? Bad RAM perhaps? I've seen bad caps as a suggestion -- would this really cause this?

    Thanks!
    -- Adrian

  2. #2
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    In my experience, yellow screen on an A500 is either bad RAM or bad Fat Agnus. Since you've already tried a different Fat Agnus, I'd guess RAM. But I've only seen this a few times, and from what I recall from the documentation, yellow isn't supposed to mean bad CHIP RAM.

  3. #3
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    Quote Originally Posted by KC9UDX View Post
    In my experience, yellow screen on an A500 is either bad RAM or bad Fat Agnus. Since you've already tried a different Fat Agnus, I'd guess RAM. But I've only seen this a few times, and from what I recall from the documentation, yellow isn't supposed to mean bad CHIP RAM.
    Indeed, bad CHIP ram is supposed to be green. I wonder if Kickstart 2.0 has different colors? I should try a Kickstart 1.3 ROM and see if that changes things.... As for bad ram, I'm dreading trying to remove those DIP chips to socket them. Have you ever had any luck with the piggy-back method?
    -- Adrian

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    The colours should be the same. I've rarely worked with 1.x so I'm not totally positive. Something tells me I've had a yellow screen on an A500 from something else and I've been wracking my brain trying to recall what it was. I'd like to say Paula but I don't know. It wouldn't hurt to pull Paula and Denise out to see if you get a different colour without them. Then maybe try putting different ones in. It's an easy thing to try in any case.

    It's been so long since I worked on an A500, and my memory stinks. Hopefully someone else chimes in.

    I've never had luck piggybacking on an Amiga. In any system I've worked on, piggybacking never makes a working system, it makes a different non-working system. A non-working Amiga is unlikely to boot either way. But at this point it wouldn't hurt to try.

  5. #5
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    Quote Originally Posted by KC9UDX View Post
    The colours should be the same. I've rarely worked with 1.x so I'm not totally positive. Something tells me I've had a yellow screen on an A500 from something else and I've been wracking my brain trying to recall what it was. I'd like to say Paula but I don't know. It wouldn't hurt to pull Paula and Denise out to see if you get a different colour without them. Then maybe try putting different ones in. It's an easy thing to try in any case.

    It's been so long since I worked on an A500, and my memory stinks. Hopefully someone else chimes in.

    I've never had luck piggybacking on an Amiga. In any system I've worked on, piggybacking never makes a working system, it makes a different non-working system. A non-working Amiga is unlikely to boot either way. But at this point it wouldn't hurt to try.
    Ok I found the issue. Guess what? the colors are NOT the same. I put in a Kickstart 1.3 and the error color changed to GREEN. Looking at the chart, that was bad chip RAM. I had done this after swapping out all the other chips (Gary, Paula, Denise, Fat Agnus, etc.) So knowing it was bad RAM, I did the piggyback test and after several tries I ended up on a chip that when I piggybacked a new RAM chip, the system worked normally! Sweet. So I'm about to remove that bad chip and hopefully get this system up and running.

    So there we go:

    Kickstart 2.04 -> Bad chip RAM = yellow screen
    Kickstart 1.3 -> Bad chip RAM = Green screen
    -- Adrian

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    Interesting. I tried to find where the colours were documented and I couldn't. I thought it was in the ROM Kernel Manuals but I didn't see it there.

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