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Thread: PET 2001-32N - Diag works in UD9, but with Kernal it fails to start

  1. #81

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    Sorry, Frank.. Just saw this. No, with UC7 removed, no cursor at all, as expected.

  2. #82

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    Quote Originally Posted by daver2 View Post

    Try bending pin 18 carefully horizontal from the PIA and re-install the IC back into the socket. Monitor both the bent pin 18 for any sign of a signal and the VIDEO ON signal again at UC5 pin 15 to narrow down the possibilities.

    Dave
    Hah.. Interesting. The pin on the PIA has no signal, but the trace has exactly the same behavior. UC5 pin 15 also shows the same behavior. More than that, I now have no cursor at all, except when that weirdo signal is happening, and then it's just a fast flickering cursor.

  3. #83

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    Quote Originally Posted by dhoelzer View Post
    Hah.. Interesting. The pin on the PIA has no signal, but the trace has exactly the same behavior. UC5 pin 15 also shows the same behavior. More than that, I now have no cursor at all, except when that weirdo signal is happening, and then it's just a fast flickering cursor.
    I've been thinking about this all day and I'm not coming up with any ideas on the potential causes. Is the consensus that this is some kind of bleed over through some sort of intermittent connection?

  4. #84

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    Could there be something flaky in the overall master timing circuit? Probing around, I see changes all the way over in UM2 pin 7 when it starts flaking out. I don't have my schematics unpacked to look up what that is just now, but I'm wondering if that's where I should be investigating (timing circuit)

  5. #85

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    Quote Originally Posted by dhoelzer View Post
    Could there be something flaky in the overall master timing circuit? Probing around, I see changes all the way over in UM2 pin 7 when it starts flaking out. I don't have my schematics unpacked to look up what that is just now, but I'm wondering if that's where I should be investigating (timing circuit)
    http://www.zimmers.net/anonftp/pub/c...N/320349-6.gif

    Start checking various signals referring to that schematic. 8 MHz, 1 MHz, 8 phases of CLK1, RAS0 first of all.
    Since you have a stable video display, I don't expect a big problem here, but you must start somewhere. Is the machine stable enough with all RAM and ROM provided from the daughterboard?
    Frank

  6. #86

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    Quote Originally Posted by iz8dwf View Post
    http://www.zimmers.net/anonftp/pub/c...N/320349-6.gif

    Start checking various signals referring to that schematic. 8 MHz, 1 MHz, 8 phases of CLK1, RAS0 first of all.
    Since you have a stable video display, I don't expect a big problem here, but you must start somewhere. Is the machine stable enough with all RAM and ROM provided from the daughterboard?
    Frank
    Yep. Seems very stable at this point, even with my bodged in replacement video RAM board. It's just the "extra" signal showing up at the PIA that seems to be all over the place (or impacting many things).

  7. #87

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    Quote Originally Posted by dhoelzer View Post
    Yep. Seems very stable at this point, even with my bodged in replacement video RAM board. It's just the "extra" signal showing up at the PIA that seems to be all over the place (or impacting many things).
    Interesting. First, after probing pin 3 on UG5 (8Mhz clock coming out of the counter), the system now boots directly into the monitor, which is an unexpected change. Second, the 1mhz output and the 16mhz input are very clean, but the 8mhz output on pin 3 is not regular, and will not measure at 8mhz... and simply probing the pin drops out the video signal. Here's the trace:
    IMG_3176.jpg
    I'll continue around the rest of the clocks.

  8. #88

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    Quote Originally Posted by dhoelzer View Post
    Interesting. First, after probing pin 3 on UG5 (8Mhz clock coming out of the counter), the system now boots directly into the monitor, which is an unexpected change. Second, the 1mhz output and the 16mhz input are very clean, but the 8mhz output on pin 3 is not regular, and will not measure at 8mhz... and simply probing the pin drops out the video signal. Here's the trace:
    IMG_3176.jpg
    I'll continue around the rest of the clocks.
    hmm weird, CLK8 as far as I remember, goes only to pin 2 of UE11, it's the "dot clock" to shift out the character generator dots on each scanned row. Check the connection between these two pins. I doubt that UE11 is injecting noise into CLK8 as it would probably result in weird displayed characters or no display at all.
    Basicly, you need a very good and clean CLK8 to have a stable display, if I'm not wrong of course.

    Frank

  9. #89

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    Quote Originally Posted by iz8dwf View Post
    hmm weird, CLK8 as far as I remember, goes only to pin 2 of UE11, it's the "dot clock" to shift out the character generator dots on each scanned row. Check the connection between these two pins. I doubt that UE11 is injecting noise into CLK8 as it would probably result in weird displayed characters or no display at all.
    Basicly, you need a very good and clean CLK8 to have a stable display, if I'm not wrong of course.

    Frank
    RAS0 is a very dirty 1mhz.. CAS1 off of G7 is only high, CAS0 is clean, but irregular and I can't seem to get a frequency reading off of it.

  10. #90

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    Quote Originally Posted by iz8dwf View Post
    hmm weird, CLK8 as far as I remember, goes only to pin 2 of UE11, it's the "dot clock" to shift out the character generator dots on each scanned row. Check the connection between these two pins. I doubt that UE11 is injecting noise into CLK8 as it would probably result in weird displayed characters or no display at all.
    Basicly, you need a very good and clean CLK8 to have a stable display, if I'm not wrong of course.

    Frank
    I think you're right, but I also think there's something a bit up since simply probing it is enough to complete disrupt the display.

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