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Thread: Commodore Pet 8032SK with monitor not working

  1. #221
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    I am not still 100% happy with the outcome so far.

    I too am still suspect of the E400 rail.

    I am also still suspect that we found two dead 'fusible' resistors and no reason why they had gone.

    Also, the machine has (if by magic) started to work without us really doing anything to it...

    Not too convinced we are 'out of the wood' yet so to speak. I am reserving judgement.

    Dave

  2. #222

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    Quote Originally Posted by Dwight Elvey View Post
    Finally a straight on picture. I was't sure if it was an issue with bypass capacitors or that the yoke was rotated. As Hugo says, be careful around the neck. If after you rotate the yoke, you don't like the centering, there are two tabs sticking out that you can use to center the display. If the two tabs are together, they are the strongest pulling things around the screen. If they are 180 out, they have no effect.
    Move them around a little and you'll get the feel. They are slightly magnetized.
    As for erratic reset, it is often that the crystal doesn't start up very fast and the reset circuit isn't slow enough. Sometime it is the IC the makes the crystal oscillator. Some times it is the crystal. Some times it is the electrolytic/tantalum capacitor in the reset. Some times you can get the crystal oscillator to start a little faster by adding a 5 pf cap on one end or the other of the crystal to ground.
    What works for you is up to you.
    I'm curious, why do you generally ignore my request? Is it that you don't like me?
    Dwight
    Sorry Dwight but i don't receive always post notify....what's your request ???
    REset seems to work...but after more or less 1 minute cursor stops blinking!

  3. #223

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    You've got something marginal in the system. Causing it to change. It won't be easy to locate unless it remains broken after powering on for some time.
    I've asked for a few measurements early on that would have save a lot of time. I've asked several times to report the scale settings with reported measured values. I've asked for pictures straight on with the bezel clearly shown twice. That still hasn't happened. The recent picture wasn't straight on enough to see it centering in the bezel.

    You can run a wire out from the circuit ground and UD16 pin 6 or 7 to make a manual reset, by shorting this point to ground. You can use a N.O. push button but just toughing the wires together is easy enough. If it stays broken after manually resetting, it will be a lot easier to trouble shoot. There are other things to try but having a manual reset will be less stress on the CRT, than cycling the power.
    I'll be off the air for a while but look back later tonight.
    Dwight

  4. #224

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    Quote Originally Posted by Dwight Elvey View Post
    You've got something marginal in the system. Causing it to change. It won't be easy to locate unless it remains broken after powering on for some time.
    I've asked for a few measurements early on that would have save a lot of time. I've asked several times to report the scale settings with reported measured values. I've asked for pictures straight on with the bezel clearly shown twice. That still hasn't happened. The recent picture wasn't straight on enough to see it centering in the bezel.

    You can run a wire out from the circuit ground and UD16 pin 6 or 7 to make a manual reset, by shorting this point to ground. You can use a N.O. push button but just toughing the wires together is easy enough. If it stays broken after manually resetting, it will be a lot easier to trouble shoot. There are other things to try but having a manual reset will be less stress on the CRT.
    Dwight
    Dwight now Pet turn on always with normal basic screen but after many seconds freeze and cursors stops blinking...
    With pet tester inserted, all works fine!
    Maybe bad editor rom???
    Thanks

  5. #225

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    Quote Originally Posted by daver2 View Post
    The RESET circuit is a C/R network driving a 555 timer. These are notoriously poor. But I am not getting feedback from an earlier post I made regarding how long the PET is left OFF for before trying it again. Too short a time period and the reset circuitry may not work.
    Dave
    Maybe when the computer powers up in an abnormal state, he could briefly short out the capacitor there and induce a good reset, to then see if it corrects itself ...What do you think ? Though now I see Dwight suggested that too.
    But now it looks like something is stopping the cursor blinking after the computer starts.

  6. #226
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    I get the impression that we are trying to solve too many problems in one go. We are following one problem and then we get another thrown into the mix.

    Can we get the alignment of the picture on the monitor itself sorted out first.

    Then look at the H, V and video signal to the monitor when we get a black screen on startup (this will tell us whether we have a monitor or mainboard issue) and then we can look to 'box up' the monitor and call that working for now.

    We can then concentrate on the PET mainboard. I would like to see my PETTESTER run on this board again. Make sure the ROM checksums are consistently OK. Checkout that all the keys work and then leave the memory test run for at least 20 full cycles.

    if that is OK, we can then look at the non-flashing cursor and anything else that emerges. There is more than a bad EDIT ROM that can cause the cursor to freeze.

    Do we agree this is a plan?

    Dave

  7. #227

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    Quote Originally Posted by daver2 View Post
    I get the impression that we are trying to solve too many problems in one go. We are following one problem and then we get another thrown into the mix.

    Can we get the alignment of the picture on the monitor itself sorted out first.

    Then look at the H, V and video signal to the monitor when we get a black screen on startup (this will tell us whether we have a monitor or mainboard issue) and then we can look to 'box up' the monitor and call that working for now.

    We can then concentrate on the PET mainboard. I would like to see my PETTESTER run on this board again. Make sure the ROM checksums are consistently OK. Checkout that all the keys work and then leave the memory test run for at least 20 full cycles.

    if that is OK, we can then look at the non-flashing cursor and anything else that emerges. There is more than a bad EDIT ROM that can cause the cursor to freeze.

    Do we agree this is a plan?

    Dave
    Hi Dave, i calibrated picture on the monitor, now it's horizontal!
    H e V signals are ok because i can see correct basic startup image on monitor...

    Now i try to run your pettester for 20 full cycles so i can see if ram are ok!

  8. #228

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    I passed more of 30 full cycles of pettester ram and all good!

    I suspect bad editor rom.....tomorrow i ll try do write a new eprom and i test!
    Thanks!

  9. #229
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    Excellent.

    You might want to check pin 4 of the CPU with your oscilloscope with the cursor flashing normally to get a ‘feel’ of what the interrupt pin ‘looks like’ under normal circumstances.

    Check the pin again when the cursor stops flashing and see if there is any difference.

    Dave

  10. #230

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    Quote Originally Posted by daver2 View Post
    Excellent.

    You might want to check pin 4 of the CPU with your oscilloscope with the cursor flashing normally to get a ‘feel’ of what the interrupt pin ‘looks like’ under normal circumstances.

    Check the pin again when the cursor stops flashing and see if there is any difference.

    Dave

    NEWS:

    Finally 8032Sk it's ok!!

    it was faulty edit eprom....i burned a new one and now it's perfect!!
    last step is to test keyboard, hopefully good!

    Thank you very much for the precious help you gave me!!

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