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Thread: PET 8032 Resurrection Help!

  1. #21

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    OK - that to me says the PET has crashed. After looking at the video signals etc. suggested by both Daves, I personally would also look for any stuck address and data lines (high or low) - or are they just floating, perhaps with the PETTEST ROM installed ... look at the lines on the ROM chips, RAM etc as faulty chips could pull the databus high or low, so check for any pins on the databus which are not wiggling appropriately, i.e. stuck high or low or floating in the middle at indeterminate logic levels.
    Last edited by AndyG; December 21st, 2018 at 07:06 AM.

  2. #22
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    Quote Originally Posted by AndyG View Post
    OK - that to me says the PET has crashed. After looking at the video signals etc. suggested by both Daves, I personally would also look for any stuck address and data lines (high or low) - or are they just floating, perhaps with the PETTEST ROM installed ... look at the lines on the ROM chips, RAM etc as faulty chips could pull the databus high or low, so check for any pins on the databus which are not wiggling appropriately, i.e. stuck high or low or floating in the middle at indeterminate logic levels.
    Andy,
    Good idea. A NOP Generator may aid in that test, and a generator is easy to make with a couple of 40 pin sockets. It will increment the address lines continuously and produce nice square waves to look at on the scope.

  3. #23
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    Does the PETTEST ROM definitely initialize the CRTC properly?

  4. #24
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    Other people have used it fine...

    It also works OK inside VICE (I use this as a test vehicle before releasing it).

    Dave

  5. #25
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    OK, I am pretty good at troubleshooting and soldering, but I have never used a scope before for this and don't really know how to operate it, so if you guys have patience, please humor me with the basics of setting it up to look at the measurements I need on the video connector. The only thing I've ever used it for in the past is to align disk drives. I was able to at least blind-adjust it to show more or less signal when I moved the heads, but that is it.

    Here is my scope (attached photo).
    Attached Images Attached Images

  6. #26
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    That scope should do the job. Use DC coupling.
    Here's the info on the Horizontal Signal.
    20 KHz frequency (15 uS pulse every 50 uS), so pick a time base between 20 uS to 50 uS.
    Signal is a 5V TTL level. If using 10X probe, set vertical sensitivity to about 0.2 V per division. If no probe, use 2V per division

    Vertical Signal is harder to see as it is a skinny pulse (0.8 mS every 16.6 mS) so the frequency is 60 Hz. Turn up intensity. Time base set to around 5 mS per division then adjust to see pulses.

  7. #27
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    They don't make them like that any more!

    First off the vertical section. Have a play and then I will describe the horizontal section.

    Under the section marked VERTICAL - on the left hand side.

    The knob marked 'position' moves the trace 'up' and 'down' the screen. Simple enough...

    On the bottom you have two off three-position switches. You can set to AC, DC or OFF.

    OFF means that the trace will not actually indicate the signal you present to the oscilloscope.

    DC means that the signal is dc coupled to the oscilloscope.

    AC means that the signal is ac coupled to the oscilloscope.

    I will come back to these terms in a minute.

    I am not sure why there are two switches of this type - unless this is a two channel oscilloscope with two traces?

    The large knob in the middle should have numbers on it and is meant to adjust the number of Volts indicated per centimetre of vertical screen.

    You have an 8 centimetre vertical screen. So, if you are trying to measure an 8V signal you could do so by moving the trace to the lowest position on the screen (with the position knob) and setting the knob to 1V/cm. The 8V will then be indicated from full bottom to full top of the screen. Alternatively, you could position the trace on the centre line and select 2V/cm. The 8V signal would then deflect the beam vertically by 8V/2V/cm = 4 cm.

    Back to our ac and dc coupling.

    If you are trying to measure a 1V signal on a 10V dc level - and you had the oscilloscope set to DC coupling, the oscilloscope beam would be changing from 10V to 11V. If you AC coupled the signal; the DC component would be removed - leaving you with the AC signal only.

    You have a 1V CAL square wave available to attach your probe to and adjust (what I think is) a CAL potentiometer on the vertical section of the oscilloscope.

    Does this make sense so far?

    Hi dave_m...

    Dave

  8. #28
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    Most of the signals you will be measuring on the PET will be 5V (max); so 1V/cm should be your general 'go-to' setting (with a x1 probe). Get a couple of 1.5 Volt batteries and have a play to become familiar with the vertical settings.

    Dave

  9. #29
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    Well, I was playing with it and the screen went dead... The scope still has power, but no trace is there anymore on the screen. I will play with it again tomorrow, but it may have died or I killed it.

  10. #30
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    I did break out the logic probe, which I do know how to use (heh) and I do get pulsing on all the RAM and ROM chips. I am pretty sure PETTEST is running, doing something, but I have no video. It would be nice if the ROM beeped once in a while to show it's doing something blind. BIOS beep codes, perhaps?

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