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Philips Msx Vg8020 no power up

Desperado

Desperado

Veteran Member
Joined
Nov 25, 2017
Messages
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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
 
Me again!!!

Schematics (and technical manual) over at http://www.zxprojects.com/images/stories/philipsvg802000sm.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
 
daver2 said:
Me again!!!

Schematics (and technical manual) over at http://www.zxprojects.com/images/stories/philipsvg802000sm.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
Click to expand...


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

Card U101 (J7 pin 1 = 4,9V)
Card U101 (J7 pin 2 = 13,2V)
Card U101 (J7 pin 3 = -12V)
 
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
 
daver2 said:
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
Click to expand...


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
 
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:
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 !
 
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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