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Type: Posts; User: Dwight Elvey

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  1. I see your three post under that title. The first...

    I see your three post under that title. The first one started by you and the last two at the end.
    Dwight
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    It is the serial part that is the problem. The...

    It is the serial part that is the problem.
    The keyboard looks to be a normal parallel keyboard. If you find a schematic for the parallel to serial converter, that is the major issue.
    Dwight
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    I have one of these boards. Mine came with an...

    I have one of these boards. Mine came with an aluminum metal front cover that has been punched out. It takes a standard S-100 cpu that has the front panel connector. Mine has some timing errors. It...
  4. You need to go back and remeasure MWRT. Your good...

    You need to go back and remeasure MWRT. Your good board can not write to memory without a pulse on MWRT. If you don't see one, YOU HAVE A MEASUREMENT ERROR!!!!!
    I see you have a digital scope. You...
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    I'd replace the IC but it still could be a dead...

    I'd replace the IC but it still could be a dead crystal. I don't trust a logic probe for analog work.
    Dwight
  6. If you have a signal on both sides of the diode,...

    If you have a signal on both sides of the diode, and nothing but a high at the other end of the wire, you have a broken connection. Check on both sides of the board. Sometimes a feedthrou is open. It...
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    Pull the 2716 out and look again. I think it is a...

    Pull the 2716 out and look again. I think it is a flaky part. Before it was showining not driving. This shows contention. Contention is really hard to locate. It could be most any device on the bus....
  8. Did you install the diode with the correct...

    Did you install the diode with the correct polarity? The banded end should go to A1 pin 11. There should be a clock there as that is the source.
    Also, what are you using to measure with? You said...
  9. On your good CPU, you can not write to memory...

    On your good CPU, you can not write to memory without MWRT pulsing to a high. It is a high speed pulse. Also SSSWDSB has to pulse low. It can not write to memory without those signals being active....
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    On the first picture of post 92, our square wave...

    On the first picture of post 92, our square wave EPROM is missing?
    I'm sure it was working on an earlier picture but it looks to be gone?
    As for the RAMs there are some things that can be done but...
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    Yes, the trailing the next ROM after the trailing...

    Yes, the trailing the next ROM after the trailing edge, where it goes high, of D8-20 is D9 data. To see the square wave of D8 at the start, you'd need to move the probe to D7-20 from D8-20. ( at leas...
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    Do remember, we are only looking at the trailing...

    Do remember, we are only looking at the trailing edge of the select from D8, so we only see the beginning of the data on D9. It might be good to look for the possible failure of the other ROMs. In...
  13. DIEN* can be driven by two sources. One is from...

    DIEN* can be driven by two sources. One is from the 8080 processor from its WR* signal. The other is from the front panel. Remember what I said about the processor, it only does two things, JUMP and...
  14. The sequencer was really a tough one to write...

    The sequencer was really a tough one to write code for. All kinds of row and column jumps. It always reminded me of playing chess or checkers. Each move dominated the next move possibilities. The...
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    The question is how can one fix it. Try moving...

    The question is how can one fix it. Try moving the ground connection closer to the signal connection. As Hugo says, there is not enough information to say much of anything.
    Dwight
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    I did some careful offsets and it looks like the...

    I did some careful offsets and it looks like the traces from the left go between the pins of the 6402. If they went to the pins, some would need to go to the read data.
    It would be much better to...
  17. When you look at the second plot of the ripple,...

    When you look at the second plot of the ripple, the first thing to notice is that the peak to peak is about 600 mv. Again, it is important to note the frequency. 60 Hz on a full wave rectification...
  18. So, the problem is not the read, it is the write....

    So, the problem is not the read, it is the write. I'll look at the schematic tomorrow morning. I've got some resting to do. We'll do some more test then.
    Dwight
  19. I don't know, it doesn't look that bad. I don't...

    I don't know, it doesn't look that bad. I don't even know what instructions are being run and which source is driving the bus. I other words, it is not useful information. Also, is the little 1 arrow...
  20. Measure the ripple with a good capacitor and...

    Measure the ripple with a good capacitor and you'll see why I was so sure it was a bad capacitor. Post the picture so that we can have it for others to see. Use the advance edit to get the picture...
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    I suspect there may be a clock wire and possibly...

    I suspect there may be a clock wire and possibly a data ready wire and a reset. I see lines going directly to the 40 pin chip. Is there a data circuit we can look at for this chip or is it one of...
  22. That is a lot of ripple. It is way too much. That...

    That is a lot of ripple. It is way too much. That is why I asked you to check it at the large capacitor. Use the negative post of the capacitor as your ground. There are two possibilities for that...
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    Yes, that is what I was referring to as the least...

    Yes, that is what I was referring to as the least power adapter.
    Dwight
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    But what is the driver chip. The signals look...

    But what is the driver chip. The signals look like they might be rs485 or rs422 instead of rs232.
    Dwight
  25. What is the vertical scale? What is the vertical...

    What is the vertical scale? What is the vertical volts per division?
    It looks like both diodes are there but i don't see a what the volts per division is.
    Is it 2 volts per division?
    Is this...
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