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Thread: Commodore pet 3032 screen full of lines

  1. #141
    Join Date
    Jun 2012
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    UK - Worcester
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    Right, so look at the schematic http://www.zimmers.net/anonftp/pub/c...N/320349-1.gif.

    You should see the address buffers at UC3 and UB3.

    These buffers take the address lines in on the left hand side of the device (as drawn), and buffer them so they emerge on the right hand side of the device (as drawn). For example, AB15 (on the CPU as pin 25 (if you remember with a frequency of 7.637 Hz)) enters the buffer at UB3 pin 11 and exits the buffer at UB3 pin 9.

    What I want you to do is to scope the AB15 address line on the CPU and get a good oscilloscope picture of the trace (and double check that the frequency is 7.637 Hz - or there about). Then move the probe to UB3 pin 11 (buffer input). You should see the same trace as previously on the oscilloscope (it should be electrically the same point). Then move your probe to UB3 pin 9 (buffer output). Once again you should see a similar trace as at the input - with the same frequency.

    Then move down to the next address line (AB14) repeating the test (CPU pin, buffer input, buffer output) check for the correct frequency and a 'nice' square wave.

    Repeat for all of the CPU address lines down AB2 (remembering that CPU pin 10 - AB1 - and CPU pin 9 - AB0 - cannot be resolved accurately enough on your oscilloscope).

    Report back when completed.

    Dave

  2. #142

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    Quote Originally Posted by daver2 View Post
    Right, so look at the schematic http://www.zimmers.net/anonftp/pub/c...N/320349-1.gif.

    You should see the address buffers at UC3 and UB3.

    These buffers take the address lines in on the left hand side of the device (as drawn), and buffer them so they emerge on the right hand side of the device (as drawn). For example, AB15 (on the CPU as pin 25 (if you remember with a frequency of 7.637 Hz)) enters the buffer at UB3 pin 11 and exits the buffer at UB3 pin 9.

    What I want you to do is to scope the AB15 address line on the CPU and get a good oscilloscope picture of the trace (and double check that the frequency is 7.637 Hz - or there about). Then move the probe to UB3 pin 11 (buffer input). You should see the same trace as previously on the oscilloscope (it should be electrically the same point). Then move your probe to UB3 pin 9 (buffer output). Once again you should see a similar trace as at the input - with the same frequency.

    Then move down to the next address line (AB14) repeating the test (CPU pin, buffer input, buffer output) check for the correct frequency and a 'nice' square wave.

    Repeat for all of the CPU address lines down AB2 (remembering that CPU pin 10 - AB1 - and CPU pin 9 - AB0 - cannot be resolved accurately enough on your oscilloscope).

    Report back when completed.

    Dave

    Thanks so much!
    Tomorrow, after my job, i'll check this!
    Good night to all members

  3. #143
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    Jun 2012
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    UK - Worcester
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    I shall be out tomorrow evening - but I will pick up your post when I get back.

    Dave

  4. #144
    Join Date
    Feb 2009
    Location
    Southern California, USA
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    2,706

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    Quote Originally Posted by daver2 View Post

    The sync pin is also suffering from the same problem.
    Yes, the effective bandwidth of that scope is very limited. It will be OK for the 20 KHz video timing circuits, but not for CPU digital pulses in the 1 MHz region.

  5. #145
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    Jun 2012
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    But it's cheap ...

    It should cover most of the PET circuitry but, as you state, is limited for the higher frequency stuff.

    What I was planning to do is to construct a small external box containing dual 4-bit TTL dividers (divide by 256). I could then connect the higher frequency (digital) clock signals to the divider chain and measure the resultant signals. Prividing the input signal is a regular clock - I should be ok to say whether the clock is the correct frequency or not. I still couldn't 'see' the waveform itself though.

    Dave

  6. #146

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    Quote Originally Posted by daver2 View Post
    I shall be out tomorrow evening - but I will pick up your post when I get back.

    Dave
    Hi Daver2 i checked all pin from cpu (AB0 to AB15) and i have same results (freq. and waves) on UB3 UC3 in and out!

  7. #147

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    Hi

    These are the correct values with the NOP GENERATOR, look at my post:

    Quote Originally Posted by Fran View Post
    These are the values with the scope

    Attachment 55608

  8. #148

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    Quote Originally Posted by ilpaninaro View Post
    Hi Daver2 i checked all pin from cpu (AB0 to AB15) and i have same results (freq. and waves) on UB3 UC3 in and out!
    I see one screen with 10 us per division. Can you use that scale on pins 9 and 10.
    Dwight

  9. #149

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    Quote Originally Posted by Fran View Post
    Hi

    These are the correct values with the NOP GENERATOR, look at my post:
    Thanks Fran

  10. #150

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    Quote Originally Posted by Dwight Elvey View Post
    I see one screen with 10 us per division. Can you use that scale on pins 9 and 10.
    Dwight
    Hi Dwight,yes these are pictures on pin 9 and 10 cpu:
    20190924_215318.jpg
    20190924_215402.jpg

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