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Thread: Apple IIe clone ASIC STK chips help required

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  1. #1
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    Default Apple IIe clone ASIC STK chips help required

    I know this is a long shot, but, I have the pictured IIe clone board shown below.

    It shows a disrupted test screen keyboard attached or not.

    Anyone have any information on this board or a source of STK 65301 or STK 65371 chips that it uses as the MMU and IOU?

    I'd appreciate any assistance with this.
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  2. #2
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    I've never been able to find much information on them.

    What I can tell you is the are the functional equivalent of the Apple 2e MMU and IOU but they are not pin compatible.
    Every clone 2e I have seen uses the chips.

    With a little effort and an apple 2e schematic it wouldn't be too hard to trace the tracks to determine the pinouts.

  3. #3
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    I agree, but, without a replacement source, what difference does the pin-out make?

    All the RAM and TTL chips have been tested, the ROM and analog chips tested by substitution, same with the CPU. That doesn't leave much else than the STK chips.
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  4. #4
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    What do you mean by "disrupted test screen"?

    If the board is running the built in diagnostics with the keyboard plugged in or out then I would expect the asics are working fine. The 2e goes into self test by holding down the closed apple key on reset, when the keyboard is plugged in there is a resistor that pulls that line low via a resistor, the line is pulled high by the keypress. With no keyboard the line floats high so the apple does a self test on power on.

    Here is the good news, the closed apple key is not connected either to the asics or the keyboard controller. That line runs to the input of a 74LS251 and it is decoded by the 74LS154 and not an asic.
    I'd trace back pin 5 of the keyboard connector, check the address lines going to the 74LS251, its output to D7 and its enable from the 74LS154. From memory the IOU does provide the course CxxxH decode but if that was faulty the video soft switching wouldn't work so you would not see the self test screen.

    Oh... also check that the resistor is indeed pulling pin 5 of the keyboard connector low.


    Quote Originally Posted by Druid6900 View Post
    I agree, but, without a replacement source, what difference does the pin-out make?

    All the RAM and TTL chips have been tested, the ROM and analog chips tested by substitution, same with the CPU. That doesn't leave much else than the STK chips.

  5. #5
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    In a nutshell, here's what I get;

    You know how the built-in test starts with alternating black and white horizontal bars, and then merges into a full white screen a couple of times before going on to test RAM?

    Mine starts with the bars, but, there are white graphic characters in the black bars (I don't know if there are any in the white bars, obviously) and sits there.

    That's what I mean by a disrupted self test.
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  6. #6
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    Strange I was sure I replied to this yesterday.

    What you are seeing is not self test the bars are the typical uninitialised RAM pattern when a board powers on with the hires mode active.
    Any problem accessing ROM or RAM will prevent the graphic mode being cleared.

    Again its not all bad news, the fact that you seeing are different values in screen RAM locations is a good indicator the MMU is functional, because it is responsible for address multiplexing and general control of the memory.
    You have a stable display, so that indicates the IOU is likely working because it generates the video sync signals and timing.

    I'd be looking for bad sockets, dry joints or fractured tracks. Start with reset and look for read activity on the ROM enable lines. If that all looked good I'd trace out the address and data lines.

    Quote Originally Posted by Druid6900 View Post
    In a nutshell, here's what I get;

    You know how the built-in test starts with alternating black and white horizontal bars, and then merges into a full white screen a couple of times before going on to test RAM?

    Mine starts with the bars, but, there are white graphic characters in the black bars (I don't know if there are any in the white bars, obviously) and sits there.

    That's what I mean by a disrupted self test.

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