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

  1. #101

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    Quote Originally Posted by iz8dwf View Post
    Do you mean UI1 (not U11)? Pin 5 is driven by pin 11 of UH10, check page 6 of the 2001N schematic and look for VIDEO ON signal.
    Again if that signal was problematic, you wouldn't see anything on screen probably.
    Frank
    Sorry, yes.

    In other news, I've again moved on to other symptoms. That has been the story of this board; as soon as one thing is resolved, other things pop up.

    @iz8dwf - Yes, sorry. My eyes aren't super anymore and I misread UI1 as U11. I'm not saying that signal is bad in any way, I'm pointing out that when the spurious signal appears over on the PIA, there are also some artifacts showing up at UI1.

    I can confirm that with the standard pettest ROM the spurious signal never seems to appear. Switching back to normal ROMs, it still drops directly to TIM and the spurious signal will appear periodically. As a reminder, it was successfully booting to BASIC as recently as last night (!!!)

    After allowing it to run the pettest for several hours, I now have incorrect characters appearing in columns 4-7, 12-15, etc., beginning with the first column as column 0. The pettest continues to run with no issue, really, other than that, though the character sets are showing some other minor corruption.. For instance, it no longer begins "ABCD" but "DEFG", or occasionally other characters that I cannot remember.

    I clearly need to stop and regroup, because I'm becoming lost in symptoms. Tell me what to probe and I'll gladly report back.

  2. #102

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    Try some cold spray on the video RAM. If you have none, I've use isopropyl alcohol and a fan. It will likely show as a thermal issue.
    Dwight

  3. #103

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    Quote Originally Posted by Dwight Elvey View Post
    Try some cold spray on the video RAM. If you have none, I've use isopropyl alcohol and a fan. It will likely show as a thermal issue.
    Dwight
    I've actually tried swapping the chips out, Dwight. I don't doubt it's somehow thermal related, but it's not the video RAM.

  4. #104

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    Quote Originally Posted by dhoelzer View Post
    I've actually tried swapping the chips out, Dwight. I don't doubt it's somehow thermal related, but it's not the video RAM.
    It would be interesting to see what's actually happening, if you could make a small video, it would surely help.
    As for dropping into the monitor at the start, check pin 9 (PA7) of UC7, if that's low, that's how it happens. Otherwise, it could happen by executing a BRK, but if you're using both RAM and ROM from the daughterboard, that can't happen (unless I miss something really).

    Frank IZ8DWF

    EDIT: it could drop to the monitor without UC7 pin 9 low if you have a data bus 7 (D7) tied low on the motherboard or a conflict at the right time, but that should be evident even when running the pettester image (post a video if you can).

  5. #105

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    Quote Originally Posted by iz8dwf View Post
    It would be interesting to see what's actually happening, if you could make a small video, it would surely help.
    As for dropping into the monitor at the start, check pin 9 (PA7) of UC7, if that's low, that's how it happens. Otherwise, it could happen by executing a BRK, but if you're using both RAM and ROM from the daughterboard, that can't happen (unless I miss something really).

    Frank IZ8DWF

    EDIT: it could drop to the monitor without UC7 pin 9 low if you have a data bus 7 (D7) tied low on the motherboard or a conflict at the right time, but that should be evident even when running the pettester image (post a video if you can).
    Ok. First, pin 9 on UC7 has a 200khz 80% duty cycle squarish wave on it before the system starts, then it's all over the place, so tough to get a good picture of what's happening there.

    I have placed a video of the system starting both the pettest ROM and the BASIC ROMs, dropping to TIM, onto my Google drive. At the beginning, you can see Pettest looks fine for a few seconds, at least. As time goes on, the display degrades. It did not exhibit the "frozen columns" behavior with groups of four columns unchanging this morning. In the video, I have the scope tied to pin 17 of UC7.

    If you look toward the end of the video, you can see that with pettest running, pin 17 never changes... but with the normal ROMs switched in, the flakey signal appears sporadically, coinciding with the fast-blink. (4:30 to 4:45 is a great place to look in for this... The longer the system is on, the more constant the spurious signal is)

    What now, guys?

    Video link: https://drive.google.com/file/d/1WH6...ew?usp=sharing

  6. #106

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    Quote Originally Posted by dhoelzer View Post
    Ok. First, pin 9 on UC7 has a 200khz 80% duty cycle squarish wave on it before the system starts, then it's all over the place, so tough to get a good picture of what's happening there.

    I have placed a video of the system starting both the pettest ROM and the BASIC ROMs, dropping to TIM, onto my Google drive. At the beginning, you can see Pettest looks fine for a few seconds, at least. As time goes on, the display degrades. It did not exhibit the "frozen columns" behavior with groups of four columns unchanging this morning. In the video, I have the scope tied to pin 17 of UC7.

    If you look toward the end of the video, you can see that with pettest running, pin 17 never changes... but with the normal ROMs switched in, the flakey signal appears sporadically, coinciding with the fast-blink. (4:30 to 4:45 is a great place to look in for this... The longer the system is on, the more constant the spurious signal is)

    What now, guys?

    Video link: https://drive.google.com/file/d/1WH6...ew?usp=sharing
    From what you describe (any signal at all on pin 9 of UC7) it must be no ground connection on UC7 socket or very badly regulated power supply (200 KHz ???). That pin is an input.
    Check the UC7 socket, check power supply regulation/noise levels.
    Frank

  7. #107

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    No, I have to give it more thought. I'm not able to view the video you have.
    Dwight

  8. #108

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    Quote Originally Posted by iz8dwf View Post
    From what you describe (any signal at all on pin 9 of UC7) it must be no ground connection on UC7 socket or very badly regulated power supply (200 KHz ???). That pin is an input.
    Check the UC7 socket, check power supply regulation/noise levels.
    Frank
    Hah! I had long suspected the power had issues but got derailed from that about ten pages ago. Let me remove the original completely and wire in something modern. I'll report back.

  9. #109

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    Quote Originally Posted by dhoelzer View Post
    Hah! I had long suspected the power had issues but got derailed from that about ten pages ago. Let me remove the original completely and wire in something modern. I'll report back.
    Alrighty. I've wired in a modern supply to feed the 7812 and 7805 regulators. Pin 9 is unchanged, as is the spurious signal. Are you thinking I should wire up a regulated +5 and +12 and feed the board directly, bypassing the on-board regulators completely?

  10. #110

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    Quote Originally Posted by dhoelzer View Post
    Alrighty. I've wired in a modern supply to feed the 7812 and 7805 regulators. Pin 9 is unchanged, as is the spurious signal. Are you thinking I should wire up a regulated +5 and +12 and feed the board directly, bypassing the on-board regulators completely?
    Onboard regulators can only have issues if the electrolytic capacitors are dried out. I just suggested you to check the power supply with the oscilloscope in AC coupling (I should have been more precise in my suggestion, sorry). Leave the original power supply and try to see if UC7 has proper ground connection and PIN 9 has no measurable continuity with nearby pins maybe. Check +5V and GND pins of UC7 when the problem starts with AC coupling on the oscilloscope... there must be something wrong around there.

    Frank

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