Image Map Image Map

Search:

Type: Posts; User: Dwight Elvey

Page 1 of 20 1 2 3 4

Search: Search took 0.13 seconds.

  1. Replies
    104
    Views
    1,472

    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...
  2. Replies
    104
    Views
    1,472

    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
  3. Replies
    119
    Views
    5,650

    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...
  4. Replies
    104
    Views
    1,472

    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...
  5. Replies
    104
    Views
    1,472

    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....
  6. Replies
    104
    Views
    1,472

    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...
  7. Replies
    104
    Views
    1,472

    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...
  8. Replies
    119
    Views
    5,650

    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...
  9. Replies
    104
    Views
    1,472

    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...
  10. Replies
    104
    Views
    1,472

    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
  11. 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
  12. 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...
  13. 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...
  14. Replies
    102
    Views
    15,627

    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...
  15. Replies
    102
    Views
    15,627

    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...
  16. Replies
    109
    Views
    3,855

    Yes, thanks Dave. The notch is always the...

    Yes, thanks Dave. The notch is always the orientation. The label is just something the manufacture put there. I get used to manufactures that have the label at the notch end and then have to switch...
  17. Replies
    104
    Views
    1,472

    Yes, that is correct. The intent is to also write...

    Yes, that is correct. The intent is to also write one bit by active control, across the entire VRAM that is addresses by the mux.
    I have to admit, it is unlikely to be SEL8.
    I suspect the effect we...
  18. Replies
    104
    Views
    1,472

    I was thinking that we could do some slightly...

    I was thinking that we could do some slightly more complex test of the data buffers. TP4-1 allows us to flush a bit on all the addresses of the RAM. We can tie a data pin low or high to flush write...
  19. Replies
    109
    Views
    3,855

    A dead EPROM will usually read as unprogrammed. a...

    A dead EPROM will usually read as unprogrammed. a few days a go, I installed one upside down. I wish the different manufactures would put the labels on a consistent end. Sometimes it is on the notch...
  20. Replies
    104
    Views
    1,472

    I just want something different then the 2114's...

    I just want something different then the 2114's you've been using for the display without the cpu in place. Just the same as you did before. With two 6550 VRAMs in place and no cpu installed. You...
  21. It is unusual. Still it is not that unusual at...

    It is unusual. Still it is not that unusual at the silicon level. A standard static CMOS memory is two inverters with high impedance PMOS transistors. There are two pass NMOS transistors connect to...
  22. Replies
    16
    Views
    476

    It is just gold scrap in a pile of pieces. One...

    It is just gold scrap in a pile of pieces. One always wonders what people think about these things. "Maybe it will be it will be worth a lot more, if I take it all apart"
    Why would anyone think it...
  23. Replies
    3
    Views
    110

    I'd really like to have a sampling scope that...

    I'd really like to have a sampling scope that small with a 2 to 5Mhz band width. Most cases that I need it that fast would be to sample repetitive signal, like clocks or dividers. I'm wondering it...
  24. Replies
    15
    Views
    490

    If it is only the DAA that is a problem the...

    If it is only the DAA that is a problem the additional 256 bytes shouldn't be an issue unless you are really tight on flash space. You could use even less space with a simple magnitude compare first,...
  25. Replies
    104
    Views
    1,472

    I'd still like to be humored with the 6550 RAMs...

    I'd still like to be humored with the 6550 RAMs in place and not CPU. I believe you may be right about the data but leaking in but there is something wrong with the address mux as well. We'd see much...
Results 1 to 25 of 500
Page 1 of 20 1 2 3 4