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Thread: Apple IIe clone ASIC STK chips help required

  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.

  7. #7
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    I don't know how much profit there would be left in a clone board after pouring all that tech time into it, so, I'll probably just set it aside in the "if your day is going too well" stack for now and work on it as a hobby thing.

    Thanks for your suggestions though, I appreciate then.
    Legacy Computers and Parts

    Sales of, parts for, and repairs to, Vintage and Legacy computers.

  8. #8
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    Try the ROM image I posted recently. It doesn't require the RAM to be fu7lly functional. What you see on the screen will give clues to here the problem is.

    https://drive.google.com/open?id=0B8...Fd0aEJhNVN6RHM

    Quote Originally Posted by Druid6900 View Post
    I don't know how much profit there would be left in a clone board after pouring all that tech time into it, so, I'll probably just set it aside in the "if your day is going too well" stack for now and work on it as a hobby thing.

    Thanks for your suggestions though, I appreciate then.

  9. #9
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    Quote Originally Posted by David_M View Post
    Try the ROM image I posted recently. It doesn't require the RAM to be fu7lly functional. What you see on the screen will give clues to here the problem is.

    https://drive.google.com/open?id=0B8...Fd0aEJhNVN6RHM
    I would LOVE to be able to burn and use the ROM you developed. I have all the files already.

    However, the seller of the first TL866CS package I ordered said it was shipped and, when I inquired if there were any numbers that might be able to track it by (there was no provision to upgrade the shipping), cancelled the order and refunded the money. It was, obviously, never shipped.

    After a month of that, I ordered another from a different supplier who didn't happen to mention that he didn't have them in stock. I had to wait an extra week, but, it shipped today (with tracking), so, when it gets here, I'll make a ROM and see what it does.
    Legacy Computers and Parts

    Sales of, parts for, and repairs to, Vintage and Legacy computers.

  10. #10
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    I had a similar issue with a phone I bought on ebay before Christmas, its frustrating. I use a TL866CS myself, the only problem I have found with it is that most of the old EPROMS are 25v VPP and cant be programmed. So the old ISA bus EPROM programmer and XT clone won't be retired just yet

    Quote Originally Posted by Druid6900 View Post
    I would LOVE to be able to burn and use the ROM you developed. I have all the files already.

    However, the seller of the first TL866CS package I ordered said it was shipped and, when I inquired if there were any numbers that might be able to track it by (there was no provision to upgrade the shipping), cancelled the order and refunded the money. It was, obviously, never shipped.

    After a month of that, I ordered another from a different supplier who didn't happen to mention that he didn't have them in stock. I had to wait an extra week, but, it shipped today (with tracking), so, when it gets here, I'll make a ROM and see what it does.

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