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Type: Posts; User: Dwight Elvey

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  1. Carry functions or increment. You can get rid of...

    Carry functions or increment. You can get rid of either add or subtract but you do need a bit wise complement.
    Dwight
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    What is with youtube dropping people and then...

    What is with youtube dropping people and then only tell them that they are in violation of a vague reason. There is no specific infraction mentioned. A couple, videos I frequent have been pulled. In...
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    This is a great idea. Fantastic idea. Dwight

    This is a great idea. Fantastic idea.
    Dwight
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    First remove D5 and then check that the 22 ohm is...

    First remove D5 and then check that the 22 ohm is no longer there, to ground.
    Many of the clock pulse are very short duty cycle in the clock control circuits. They are not all square waves. That is...
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    This is clearly your problem. At 22 ohms, D5 pin...

    This is clearly your problem. At 22 ohms, D5 pin 5 and D2 pin 11 are clearly connected through something that is about 22 ohms to the ground lead.
    I can't think of anything other than a failed part...
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    I would also like to see your solder joints in...

    I would also like to see your solder joints in the D2 socket. I only ask this because I have no idea of your soldering skills. Please don't take offence if you are generally proud of your soldering...
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    There is nothing wrong with a machine pin socket....

    There is nothing wrong with a machine pin socket. As a matter of fact I always recommend them. You just have to be careful if there are traces between socket pins, as are typical on two sided boards....
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    It is likely the same as TI's that is online...

    It is likely the same as TI's that is online someplace. The most common thing that changed on the early ones was the current limit.
    I'd like the GAL information myself. TI shows the fuse mapping as...
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    I don't know the path between D5 and D2. It is...

    I don't know the path between D5 and D2. It is likely shorted on that path to another signal. Power off and ohm meter, one lead on D5 pin 5 to each of the pins of D2. The only pin it should be...
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    The first place I'd look is C6 pin 13 is low and...

    The first place I'd look is C6 pin 13 is low and not pulsing. Something he did on D2 has killed one of the flops on D5.
    If so C6 pin 13 will not be pulsing and is stuck low.
    Assuming it is...
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    The first place to look is at the unsolder job...

    The first place to look is at the unsolder job you did. Get the schematic out and start tracing with an ohm meter from every point you touched. It is really easy to break a feedthrou when removing a...
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    With all the chips in place, what is the logic...

    With all the chips in place, what is the logic level on D2 pin 1?
    Dwight
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    The word "CREATE" is simple but the word "DOES>"...

    The word "CREATE" is simple but the word "DOES>" is trickier.

    : CREATE VARIABLE -2 H +! ;

    "DOES>" needs to find the last word being created. It could compile the code field of the last word in...
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    Again, we are looking at it with the CPU removed...

    Again, we are looking at it with the CPU removed and the pin 39 is not driven. 39 is attached to MOS inputs that likely have pullups on their inputs of some sort to be compatible with TTL. With the...
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    I should note that in the picture, the left...

    I should note that in the picture, the left bottom shows some vignetting in the lower right. There are usually a pair of magnet rings on the back of the yoke that can be used to center the screen....
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    This explains much of what we were seeing. D2 is...

    This explains much of what we were seeing. D2 is stuck seeing the CPU's address bus and not switching to the display's address counter. A low in pin 1 would indicate that the A ports should be...
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    The VROM is likely a MOS transistor input. To...

    The VROM is likely a MOS transistor input. To work correctly with TTL, it often has a pull up resistor or some source current that will likely pull the input above a TTL level. This explains the HI...
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    The "CREATE DOES" is quite useful to have. It is...

    The "CREATE DOES" is quite useful to have. It is hard to think about. The CREATE ( or in early Forth's, <BUILDS ) has the part that allocates the space and name of the thing that will be attached...
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    It has been a while since I looked at a Pet but...

    It has been a while since I looked at a Pet but as I recall, there are numbers and letters along two sides of the board. The locations are rows and columns of the boards.
    I believe A is the row at...
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    You didn't mention pin 7. It should be high....

    You didn't mention pin 7. It should be high.
    Again with the CPU removed.
    Also measure D2 pins 1 and 6. Pin 1 should be low and pin 6 should be high.
    D2 pins 11 and 14 should pulse.
    Dwight
  21. First try adjusting the vertical hold. but I...

    First try adjusting the vertical hold. but I admit, it looks like possible video ram addressing failure. It is hard to tell in a static picture.
    Dwight
  22. It would be good if they can find a benefactor...

    It would be good if they can find a benefactor that can afford to pay the rent and have some security. This would be to hold it in stasis until things get better. Someone like Paul Allen or Bill...
  23. A lot of the protocol is done by holding the...

    A lot of the protocol is done by holding the clock. It tells the other end to wait while it is busy. My guess is that it does part of the sequence but at some point it tells the PC end to wait and...
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    Then you should have said that. My earlier post...

    Then you should have said that. My earlier post was stating that one could work from a schematic, it was possible to write the code to make it work.
    Your statement was without the PROM, it couldn't...
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    Although, not easy, one can write their own boot...

    Although, not easy, one can write their own boot loader. It is software and assembly level stuff but not rocket science. I was putting together a NC4000 system. It is not anything like a...
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