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Thread: Philips Msx Vg8020 no power up

  1. #1

    Default Philips Msx Vg8020 no power up

    Hi guys i'm back after your help and success on my Pet 8032sk!
    Now please i ask help for my Philips Msx Vg8020....when i turn on, nothing happen
    and led doesn't lights
    I checked the 3 fuses but they are ok....
    Can someone help me to repair it?
    Thanks!
    20191117_174149.jpg

  2. #2
    Join Date
    Jun 2012
    Location
    UK - Worcester
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    Me again!!!

    Schematics (and technical manual) over at http://www.zxprojects.com/images/sto...vg802000sm.pdf (assuming this is the same machine as you have of course).

    Same rules apply as for the PET.

    Check the dc voltage outputs from the power supply first (card U101 is the power supply board):

    Card U101 (J7 pin 1 = +5V).
    Card U101 (J7 pin 2 = +12V).
    Card U101 (J7 pin 3 = -12V).

    All relative to 0V on card U101 J7 pin 4.

    Dave

  3. #3

    Default

    Quote Originally Posted by daver2 View Post
    Me again!!!

    Schematics (and technical manual) over at http://www.zxprojects.com/images/sto...vg802000sm.pdf (assuming this is the same machine as you have of course).

    Same rules apply as for the PET.

    Check the dc voltage outputs from the power supply first (card U101 is the power supply board):

    Card U101 (J7 pin 1 = +5V).
    Card U101 (J7 pin 2 = +12V).
    Card U101 (J7 pin 3 = -12V).

    All relative to 0V on card U101 J7 pin 4.

    Dave

    Hi Daver!!!
    Happy to see you again!
    You're great...you save my Pets and now are you able also with Msx???Super!

  4. #4
    Join Date
    Jun 2012
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    Default

    It's a computer with a power supply and a microprocessor.

    Once you can fix one...

    Dave

  5. #5

    Default

    So:

    Card U101 (J7 pin 1 = 4,9V)
    Card U101 (J7 pin 2 = 13,2V)
    Card U101 (J7 pin 3 = -12V)

  6. #6
    Join Date
    Jun 2012
    Location
    UK - Worcester
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    The +12V rail looks a little high - but we found that with the PET when we measured stuff didn't we?

    Logic probe time on the Z80 CPU (U3)... Let me know whether the pin(s) are high, low or pulsing. Most of these are control signals and will give me a good indication of what the CPU is up to!

    Pin 26 (/RESET). This pin should be high. If you press the RESET button, this pin should go low when the button is pressed and go high again when the button is released.
    Pin 16 (/INT).
    Pin 24 (/WAIT).
    Pin 19 (/MREQ).
    Pin 20 (/IORQ).
    Pin 21 (/RD).
    Pin 22 (/WR).
    Pin 27 (/M1).
    Pin 28 (/RFSH).

    Pin 18 (/HALT).

    Dave

  7. #7

    Default

    Quote Originally Posted by daver2 View Post
    The +12V rail looks a little high - but we found that with the PET when we measured stuff didn't we?

    Logic probe time on the Z80 CPU (U3)... Let me know whether the pin(s) are high, low or pulsing. Most of these are control signals and will give me a good indication of what the CPU is up to!

    Pin 26 (/RESET). This pin should be high. If you press the RESET button, this pin should go low when the button is pressed and go high again when the button is released.
    Pin 16 (/INT).
    Pin 24 (/WAIT).
    Pin 19 (/MREQ).
    Pin 20 (/IORQ).
    Pin 21 (/RD).
    Pin 22 (/WR).
    Pin 27 (/M1).
    Pin 28 (/RFSH).

    Pin 18 (/HALT).

    Dave

    Pin 26 (/RESET). pin go low when the button is pressed and go high again when the button is released.
    Pin 16 (/INT). HIGH
    Pin 24 (/WAIT). PULSE
    Pin 19 (/MREQ). PULSE
    Pin 20 (/IORQ). PULSE
    Pin 21 (/RD). PULSE
    Pin 22 (/WR). PULSE
    Pin 27 (/M1). PULSE
    Pin 28 (/RFSH). PULSE

    Pin 18 (/HALT). HIGH

  8. #8
    Join Date
    Jun 2012
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    UK - Worcester
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    So, the Z80 appears to be executing ...

    When you say "the LED doesn't light", which LED do you mean? There is a power LED and a CAPS LED. The power LED should illuminate (it comes directly off the +5V supply and we know that is OK).

    What have you got the computer connected to in the way of a monitor?

    Exactly which model of machine is it that you have got?

    Dave
    Last edited by daver2; November 18th, 2019 at 02:20 PM.

  9. #9

    Default

    Hi Daver2!
    Good news, i don't know why but now msx works!
    i disconnected supply connectors for your suggest tests and when i riconnected they, computer run!!
    You are like a Jesus!Now i believe in the miracles!!
    Thanks you very much !

  10. #10
    Join Date
    Jun 2012
    Location
    UK - Worcester
    Posts
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    After that pesky PET the Law of averages has to give you a simple fault !

    What’s next to repair (he says being cocky!).

    Dave

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