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Thread: CBM 8032 - What does the startup chirp actually mean?

  1. #41
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    Hi Daver2 and Dave_M,

    I have completed the surgery on the motherboard, removed the 6545-1, put in a socket and a new Motorola 6845P. I think we have some progress... For the first time I see something on the screen. Unfortunately, just a single line (See attached). The line was very bright, so I switched it off quickly.

    Any thoughts?
    Thanks
    MikePET_has_a_line.jpg

  2. #42
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    sorry, I forgot to mention that I am now seeing activity on J7 on the Video, Horizontal drive and vertical drive pins (so, the new CRTC seems to be working) - so, the fact that the monitor only displays a single horizontal line - does this mean that there is a problem on the CRT board?

  3. #43
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    No 60 Hz pulse Vertical sync on UB13 pin 40 and J7 pin 3?

  4. #44
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    Hi Dave_M,

    This is what I see on Pin 40 of UB13 and J7 Pin3PET-CRTC_Pin40.png

  5. #45
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    Quote Originally Posted by MikeP View Post
    Hi Dave_M,

    This is what I see on Pin 40 of UB13 and J7 Pin3PET-CRTC_Pin40.png
    That is noise. The signal should be 60 Hz frequency (16.67 mS period). There should be a skinny negative pulse every 16.67 mS. Use a negative edge sync with a time base of about 5 mS/ division. The vertical should be about 2 V/div with a 1X probe or .2V/div with a 10X probe.

    See http://www.zimmers.net/anonftp/pub/c.../321450-03.gif , photo3.

  6. #46
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    One step forwards ...

    +1 for Dave’s post.

    Dave

  7. #47
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    Hi Dave_M and Daver2,

    I have made several attempts to find something on the Vertical Sync pin, but, I am 99% sure it is just stuck at -5Volts with only +- 200mVolts of noise.

    Mike

  8. #48
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    Back in post #42 you stated that you saw activity on the H, V and Video pins of J7?

    In post #47 you state Ďstuck at -5Ví. Do you mean +5V?

    I am not doubting you, but can we make sure that we are not getting ourselves confused before we move on.

    Dave_m suggested an oscilloscope setting to measure the V DRIVE back in post #45. Have you used those settings?

    Do you have a logic probe? if so, can you probe the H, V and Video pins of J7 (with no monitor connected) fir signs of activity please and report if the pins are High, Low or Pulsing please.

    I am suspecting a monitor fault, but (for this to be true) we need to see all 3 signals as correct from the PET! I would just like to make it 100% that we donít have an operational V Drive signal...

    Cheers,

    Dave

  9. #49
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    Quote Originally Posted by daver2 View Post
    I would just like to make it 100% that we donít have an operational V Drive signal...
    Yes, it is important to know the proper voltage on the Vertical drive signal. If we have a noisy LOW level signal then we may suspect a shorted signal. +/- 200 mV is a lot of noise. Do you see this on other signals?

    Also let's keep the J7 connector disconnected from the monitor until the H and V sync signals are correct to protect the CRT. This is a difficult problem. Hang in there.
    -dave_m

  10. #50
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    Thanks for the encouragement. Attached is the output from Pin 3 (Vertical Drive) of J7. (I have kept the monitor disconnected). I think the scope is setup as Dave_M requested. (I see a square wave on the Video pin and Horizontal drive).

    SDS00006.png

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