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Thread: Fat agnus alignment

  1. #1
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    Default Fat agnus alignment

    Just checking to make sure I've got this right... I have a once working A500 that now goes to a green screen (chip ram). I was told to check the fat agnus just in case... it looks fine.. pins in socket look ok.. but wanted to check alignment.. with PLCC chips, you go by where the place the dot on the chip and in the socket, right?

  2. #2

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    The dot points to pin one, and may be marked as such in the silkscreen.

    But there's also a keyed corner which is keyed in the socket. The key is in the form of a chamfer. You can still force the chip in the wrong way, in which case the socket will break.

    If it's in the wrong way, I'm pretty sure you won't even get a green screen.

    It wouldn't hurt to pop it out and reseat it. But I wouldn't bank on it helping.

    Do you have a trapdoor RAM card? If so remove it. Also check for corrosion on the motherboard due to it.

  3. #3
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    Thanks yeah I think we've got this correct.

    This was a good working A500 that I borrowed some ICs from to troubleshoot my A1000. But even with the original chips back we're getting green screened. There's no trapdoor RAM, so now I'm down to figuring out which of the (soldered.. ugh) RAM chips it is.

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    Hrmm.. maybe it's not RAM.. I thought it was freezing at the green screen but it's not.. if you wait it out a couple of seconds it does some weird screen theatrics and then goes to a grey screen.

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    NM. Turned out to be bad CPU. I borrowed the 68010 from my MC68000 and suddenly it sprang to life.

  6. #6

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    I've had problems give me the green screen multiple times and have never had bad RAM, but don't recall what any of those problems were. But you figured it out anyway.

    So now I wonder if you your parts swapping caused the dead 68000. If so, you're closer to figuring out the A1000.

  7. #7
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    Well it turned out the 68000 in question wasn't dead.. there was one pin bent inwards. I'm usually pretty careful but this missed my attention. I've got 5 68000 CPUs lying around and the 500 boots on all of them.

    However in the original 1000 board.. zero. Just a frustrating black screen. I've now checked and rechecked all socketed chips. I even borrowed the daughterboard from my good 1000 but nada. The only obviously broken thing on it is that delay line device.. don't know what they are called. Has three legs.. one is broken. But I'm told that's only for composite video. And even if I was inclined to fix it, there's no part available. Could be bad TTL somewhere.. who knows.

  8. #8

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    It's called just that, a delay line. And you're right, it shouldn't cause that problem.

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