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Thread: Commodore Pet 8032SK with monitor not working

  1. #251

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    Quote Originally Posted by Dwight Elvey View Post
    I do see no other Horizontal unfiltered control than this path.
    Dwight
    Can Rifa capacitor causing this problem?i founded this rifa on pet case but not soldered...

  2. #252

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    Quote Originally Posted by ilpaninaro View Post
    Can Rifa capacitor causing this problem?i founded this rifa on pet case but not soldered...
    Ilpaninaro,

    I think Dwight and I are distracting you from your current computer problem. We are just talking about the theory behind the capacitor and its circuit on the lower right of the monitor's schematic diagram. It is not related to your fault in any way.

    The Rifa capacitors are used on the line power input circuitry to filter our radio frequency interference that might be there. You will see them on all sorts of equipment. They are notorious for failing and producing smoke, so rather than replacing them, some people just cut them out of the circuit. Everything still works ok without them, though the appliance may be more susceptible to, or produce more radio frequency interference.

    The problem with a lot of the Rifa capacitors, is that they were made from a metalized paper film. They were called "self healing" which is a misnomer that means when a voltage spike comes along it eats away the film,mostly, rather than shorting out, so the capacitance drops with time. Also, the plastic cases they in are often in crack, this lets in moisture and the paper expands and they swell up. The effect is they do often short out & smoke up despite their ratings. These capacitors are called X2 or Y types depending on the connections and have special fire retardant ratings and are approved to be connected across the line power, so if you replace them it must be an approved part for the application. There are better quality plastic film X2 types available these days for replacements.

  3. #253

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    Quote Originally Posted by Hugo Holden View Post
    Ilpaninaro,

    I think Dwight and I are distracting you from your current computer problem. We are just talking about the theory behind the capacitor and its circuit on the lower right of the monitor's schematic diagram. It is not related to your fault in any way.

    The Rifa capacitors are used on the line power input circuitry to filter our radio frequency interference that might be there. You will see them on all sorts of equipment. They are notorious for failing and producing smoke, so rather than replacing them, some people just cut them out of the circuit. Everything still works ok without them, though the appliance may be more susceptible to, or produce more radio frequency interference.

    The problem with a lot of the Rifa capacitors, is that they were made from a metalized paper film. They were called "self healing" which is a misnomer that means when a voltage spike comes along it eats away the film,mostly, rather than shorting out, so the capacitance drops with time. Also, the plastic cases they in are often in crack, this lets in moisture and the paper expands and they swell up. The effect is they do often short out & smoke up despite their ratings. These capacitors are called X2 or Y types depending on the connections and have special fire retardant ratings and are approved to be connected across the line power, so if you replace them it must be an approved part for the application. There are better quality plastic film X2 types available these days for replacements.
    Great!Thanks!!

  4. #254

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    In any case, Hugo didn't say, it is not related to your problem. They are there mainly to block RF interference from your computer to the outside world. As Hugo says, these often fail and for the most part we just remove them. They do block some sources of power spikes from entering your machine but can't block large spikes, such as a 5 horse motor on the same power line.
    The first thing you need to do is put a reset switch on to see if the failure is immediate or delayed after a reset. Turning the power off, even for a second, lets things cool off.
    If it fails immediately, it will be easier to locate with something like a cotton swab wetted with alcohol. You can then cool off a single part by wetting it and then doing a reset to see if it makes a difference. If it delays the failure, you have likely found the offending part or at least a part that is in the accumulative path of the failing part.
    Dwight
    Last edited by Dwight Elvey; November 7th, 2019 at 03:32 PM.

  5. #255
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    So, after that distraction...

    What we still need is a further oscilloscope trace (with the same oscilloscope configuration) of CPU pin 4 when your cursor stops flashing to compare the previous trace to.

    Dave

  6. #256

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    Quote Originally Posted by daver2 View Post
    So, after that distraction...

    What we still need is a further oscilloscope trace (with the same oscilloscope configuration) of CPU pin 4 when your cursor stops flashing to compare the previous trace to.

    Dave

    Hi,
    unfortunately this problem it's intermittent.....sometimes cursor stops blinking and sometimes run correctly...
    But now i tested a datasette in both pet ports but doesn't work!!! No ffw no rrw and not play also if i digit load and return...

  7. #257
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    3,155

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    >>> unfortunately this problem it's intermittent.....sometimes cursor stops blinking and sometimes run correctly...

    Ok, but you know what to look at and post when it next occurs. If the problem is temperature related (although now you say it is intermittent it may not be after all) you may be able to provoke a failure by heating up various parts of the board with a hairdryer (set to hot).

    >>> But now i tested a datasette in both pet ports but doesn't work!!! No ffw no rrw and not play also if i digit load and return.

    First off, look at the PET main board schematics and measure the power supply voltages on the edge connector.

    You should find the schematics/manuals here http://www.zimmers.net/anonftp/pub/c...tte/index.html.

    I am not sure which unit you have but page 3 of http://www.zimmers.net/anonftp/pub/c...(1984_Oct).pdf has a faultfinding flowchart...

    Dave
    Last edited by daver2; November 8th, 2019 at 10:44 AM.

  8. #258

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    Quote Originally Posted by daver2 View Post
    >>> unfortunately this problem it's intermittent.....sometimes cursor stops blinking and sometimes run correctly...

    Ok, but you know what to look at and post when it next occurs. If the problem is temperature related (although now you say it is intermittent it may not be after all) you may be able to provoke a failure by heating up various parts of the board with a hairdryer (set to hot).

    >>> But now i tested a datasette in both pet ports but doesn't work!!! No ffw no rrw and not play also if i digit load and return.

    First off, look at the PET main board schematics and measure the power supply voltages on the edge connector.

    You should find the schematics/manuals here http://www.zimmers.net/anonftp/pub/c...tte/index.html.

    I am not sure which unit you have but page 3 of http://www.zimmers.net/anonftp/pub/c...(1984_Oct).pdf has a faultfinding flowchart...

    Dave
    Datacassette works on C64 but not in Pet...i have 5v on pin 2 of J3

  9. #259
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    Jun 2012
    Location
    UK - Worcester
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    3,155

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    That’s good to know.

    Do you have a 0V rail as well?

    Measure the voltage between J3 pin 1 (0V) and J3 pin 2 (+5V).

    Dave

  10. #260

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    Quote Originally Posted by daver2 View Post
    Thatís good to know.

    Do you have a 0V rail as well?

    Measure the voltage between J3 pin 1 (0V) and J3 pin 2 (+5V).

    Dave
    J3 pin1 to pin2= 4,22V

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