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Thread: cbm 8032 rusty and dead

  1. #11

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    i have a rom ram replecement of tynemouth card, when i use it led is on but don't any other, i check all chip logic and replace all out of order

  2. #12

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  3. #13
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    Is this a video with a NOP generated connected - or something else on the CPU?

    Dave

  4. #14
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    Quote Originally Posted by daver2 View Post
    Is this a video with a NOP generated connected - or something else on the CPU?

    Dave
    After he checks the power voltages for the dynamic RAM, is it time for the PETTESTV4 EPROM?

  5. #15

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    Quote Originally Posted by daver2 View Post
    Is this a video with a NOP generated connected - or something else on the CPU?

    Dave
    yes, NOP generator connected, check the video on oscilloscope signal, data bus is abnormal waveform, i think a 74ls244 defect o short circuit on data bus?

  6. #16

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    Quote Originally Posted by dave_m View Post
    After he checks the power voltages for the dynamic RAM, is it time for the PETTESTV4 EPROM?
    Iesterday i write an eprom 2716 with test program pet from VCFED.org bat nothing on computer, black screen of dead, i have check the eprom on other pet and it's full function.
    I look on oscilloscope a bad waveform signal on data bus cpu, check the video please, i think a bad buffer data bus 74ls244.

  7. #17
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    Quote Originally Posted by Xchip View Post
    I look on oscilloscope a bad waveform signal on data bus cpu, check the video please, i think a bad buffer data bus 74ls244.
    It is difficult to tell anything from the video without knowing what signal we are looking at. Note that the data lines will have periods of no activity where signals will be tri-state (open) due to areas at $8800-8FFF and E800-E8FF where there will be no chip selects to turn on devices.

    You might have a bad kernel ROM, bad address line or a bad data line. With the NOP Generator installed, check that from A0 through A15, the frequency of the square waves of half of the previous address line. Look for dead shorts or opens on any address or data line. Did you check the +5V, -5V and the +12V on a dynamic RAM chip?

  8. #18
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    +1.

    Follow dave_m's advice here.

    Dave

  9. #19

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    tonight I worked with the oscilloscope, following the abnormal signal I was talking about I discovered a chip out of post, at the post of a 74ls373 there was a 74ls244, which I resolved the anomaly.
    but I noticed another problem, on the pin of the cpu db8 the signal is abnormal so this seems to be missing a connection or a defective chip, I replaced 74ls244 and 7425 on that line without success, it happens that while I measure that the signal suddenly returns almost normal and on the video something appears but then the defect returns, I am working on this belief of being on the good track but I don't know there are other defects, if you have suggestions for me I am grateful, thanks
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  10. #20

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    I tested working voltages a long time ago and replaced all defective chips with new ones, I'm pretty sure the RAM is working.
    I found a wrong chip in ud8, there was a 74ls244 instead of a 74ls373, the anomaly on the data bus and disappeared.
    But I found another problem, the cpu signal on the PIN17 signal AB8 is abnormal, it could be a short circuit or a defective chip but I have not yet understood where the problem is, I have already replaced on that line a 74ls244 and a 7425 without success, at the moment the cpu is no longer blocked and the NOP generator is no longer needed, while I was analyzing the signal with the oscilloscope it suddenly came back to normal and a very confusing image appeared on the video even if I gave repeated reset, but then the defect came back, I presume that if I solve this problem maybe I also have a fault on the video part.

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