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Thread: Commodore Pet 8032SK with monitor not working

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  1. #1

    Default Commodore Pet 8032SK with monitor not working

    Hello guys, i'm sorry but im still here asking for help please!
    I have a Cbm Pet 8032 SK 100% working but with monitor not working....
    Can someone help me repair it please?
    Thanks so much!

    Ps: orange light in cinescope works

    20191020_173650.jpg
    20191020_173657.jpg
    20191020_174037.jpg

  2. #2
    Join Date
    Jun 2012
    Location
    UK - Worcester
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    Default

    I'll start us off then...

    Board layout: http://www.zimmers.net/anonftp/pub/c...032/321449.gif

    Schematic: http://www.zimmers.net/anonftp/pub/c...032/321448.gif

    If you use your multimeter (to read 20 V dc full scale) to measure the voltage on both ends of inductor L721 (with reference to GND/0V) you should find approximately 18 V dc on both sides of inductor L721. If it was me, I would solder a black wire onto a convenient GND/0V point and use that as one side of my measurements, and two wires (one on each side of inductor L721) to remotely read the voltage. That keeps your fingers (and more importantly your heart) well away from the high voltage innards!

    I have just found TP1 on the PCB layout - that should be 18 Volts dc (and is probably easier to get than L721).

    You will notice on the schematic numbered points. These relate to oscilloscope readings that you will find in the directory http://www.zimmers.net/anonftp/pub/c...ters/pet/8032/.

    Do ***NOT*** attempt to read any voltages above 35 Volts (or so) with your little oscilloscope.

    You should be able to view the video, horizontal and vertical signals as they enter the monitor PCB from the main board on your oscilloscope and they should look like the identified waveforms numbered as (1), (13) and (3) respectively.

    You should be able to follow the video signal (1) and (2). Note that (2) is approximately a 30 Volt signal - so 5 Volts/division is required on the oscilloscope.

    You should also be able to follow the vertical drive signal all they way through on the oscilloscope. The highest voltage looks to be in the range 18V to 20V.

    The horizontal drive circuitry requires much more care - as this is where there are high voltages. Let's look at that one last...

    Dave

  3. #3

    Default

    Thanks so much Daver2, you re always great!
    I try to check your suggest

  4. #4
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    3,218

    Default

    No problem. I was sat here working on my Parallax Propeller project for work anyhow...

    Dave

  5. #5

    Default

    Quote Originally Posted by daver2 View Post
    I'll start us off then...

    Board layout: http://www.zimmers.net/anonftp/pub/c...032/321449.gif

    Schematic: http://www.zimmers.net/anonftp/pub/c...032/321448.gif

    If you use your multimeter (to read 20 V dc full scale) to measure the voltage on both ends of inductor L721 (with reference to GND/0V) you should find approximately 18 V dc on both sides of inductor L721. If it was me, I would solder a black wire onto a convenient GND/0V point and use that as one side of my measurements, and two wires (one on each side of inductor L721) to remotely read the voltage. That keeps your fingers (and more importantly your heart) well away from the high voltage innards!

    I have just found TP1 on the PCB layout - that should be 18 Volts dc (and is probably easier to get than L721).

    You will notice on the schematic numbered points. These relate to oscilloscope readings that you will find in the directory http://www.zimmers.net/anonftp/pub/c...ters/pet/8032/.

    Do ***NOT*** attempt to read any voltages above 35 Volts (or so) with your little oscilloscope.

    You should be able to view the video, horizontal and vertical signals as they enter the monitor PCB from the main board on your oscilloscope and they should look like the identified waveforms numbered as (1), (13) and (3) respectively.

    You should be able to follow the video signal (1) and (2). Note that (2) is approximately a 30 Volt signal - so 5 Volts/division is required on the oscilloscope.

    You should also be able to follow the vertical drive signal all they way through on the oscilloscope. The highest voltage looks to be in the range 18V to 20V.

    The horizontal drive circuitry requires much more care - as this is where there are high voltages. Let's look at that one last...

    Dave
    Hi Daver2,
    i saw TP1 voltage on pcb and i read 23,2 V...
    where i can see video signal with scope??
    Thanks

  6. #6
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    3,218

    Default

    23.2 Volts is too high. It should be 18.0 Volts. Is the regulator (IC901) short circuit?

    Can you measure the voltage on all three terminals of IC901 please. One pin will be the input voltage; one pin will be ground and the third pin should be the output voltage. We can work out which ones they are when you have measured them...

    To measure the video signal, look on the schematic I referenced for the video signal. This is associated with the number (1) which is connected to the 'bar' of D201. That is where to measure the signal.

    Dave

  7. #7

    Default

    Quote Originally Posted by daver2 View Post
    23.2 Volts is too high. It should be 18.0 Volts. Is the regulator (IC901) short circuit?

    Can you measure the voltage on all three terminals of IC901 please. One pin will be the input voltage; one pin will be ground and the third pin should be the output voltage. We can work out which ones they are when you have measured them...

    To measure the video signal, look on the schematic I referenced for the video signal. This is associated with the number (1) which is connected to the 'bar' of D201. That is where to measure the signal.

    Dave
    ok,
    IC901:

    INPUT:32V
    OUTPUT:23,6V

  8. #8
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
    3,218

    Default

    It's obviously regulating the voltage (so it isn't short circuit). But it is either still too high, or your multimeter is reading high, or there is a lot of ripple.

    Can you measure the DC voltage with your oscilloscope instead? DC coupling, 5Volts/division and 10 ms/division.

    See what the oscilloscope indicates for comparison.

    Dave

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