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Thread: Internal diagnostics looping on IIe enhanced

  1. #1

    Question Internal diagnostics looping on IIe enhanced

    I just picked up a IIe to give to a friend as a gift (and get him hooked on vintage machines) and when switched on it enters the internal diagnostics without any intervention from me. The display is the usual shifting garbage and the beeps happen, but instead of "SYSTEM OK" it keeps doing this over and over again. If I use the keyboard and force it to go into diagnostics it will go thought the tests, beep and display "SYSTEM OK". It won't boot or enter basic though. I've removed and re-seated the socketed IC's and thoroughly cleaned and inspected the board. It has no rust or contaminants on it and in fact didn't really need cleaning other than for the dust on it.

    Any ideas?

  2. #2

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    I know a bad keyboard (and related circuitry) can cause this, and I had one in which bad zero page RAM caused this. But there are probably other things which others will hopefully bring up.

    Welcome, by the way, and nice avy!

  3. #3

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    A stuck closed apple key will cause diagnostic at power on and the same port is also used as a game controller button.
    That feeds the LS251 at location C12 so that chip could be suspect.

    Larry G
    Last edited by retrogear; November 12th, 2017 at 07:56 PM.

  4. #4

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    Quote Originally Posted by KC9UDX View Post
    I know a bad keyboard (and related circuitry) can cause this, and I had one in which bad zero page RAM caused this. But there are probably other things which others will hopefully bring up.

    Welcome, by the way, and nice avy!
    Thanks. Love me my Amigas (all 9 of 'em).

    It acts in the exact same manner with and without the keyboard plugged in. My board has soldered RAM so that will be the last thing I check. #Lazy



    Quote Originally Posted by retrogear View Post
    A stuck closed apple key will cause diagnostic at power on and the same port is also used as a game controller button.
    That feeds the LS251 at location C12 so that chip could be suspect.

    Larry G
    With the same issue occurring when there is no keyboard connected perhaps the LS251 is the problem. Mine is at location B-C 12 due to this being a factory IIe Enhanced and is unfortunately not socketed. With luck someone will will know this issue personally and have some solution my limited soldering experience will not interfere with.

  5. #5

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    When no keyboard is connected, it's supposed to go into diagnostics just like you are describing.

    You can force the input at the '251 (via the game connector). If that works, you have a keyboard problem (which also should be easy to verify with a multimeter). If not, replacing the '251 is likely the next step. Here's your chance to get good at soldering.

    I don't have the schematics so I can't be much help. But you can trust Larry, he won't steer you wrong.

  6. #6

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    To check further, if you have a multimeter, you could measure pin 2 of the LS251 to ground. Should be 0V and 470 ohms to ground because of resistor R1. It goes to 5V when solid apple pressed. If any voltage on that pin with no key, then either open resistor path or chip is bad.

    Larry G

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