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MAGIK

JPM IMPACT CPU drawings - fan made!

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BEFORE YOU GUYS ALL FALL OVER, THESE ARE NOT THE FACTORY SCHEMATICS....

If such a thing exists no one is letting anyone know that they have got them .. so as I have a shedload of them to look at , and I was really fed up guessing what did what, I decided to sit for a few hours and work out where everything was..

 

I have scanned in the drawings I did as well,  now remember, they are drawn by me,  I checked , checked and checked again that they were right but guys better informed than me will know better -  The point is, I at least have a good idea of what everythings doing and I hope you boys and girls can make some use of them!!

 

img20190119_13231434.pdf

img20190119_13261455.pdf

img20190119_13293437.pdf

img20190119_13313123.pdf

img20190119_13334240.pdf

img20190119_13361830.pdf

img20190119_13383039.pdf

img20190119_13431475.pdf

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Just a note - X refers to an edge connector pin .  And theres no pull up on halt pin.

 

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Just out of interest, what makes you think it's a DJP design? His designs usually have his initials silk-screened onto the PCB don't they?

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Meh,  I thought he had his hand in all the impact stuff.  I could be wrong!!!!

You know what its like in videos tho, sometimes you waffle on, and then correct your mistakes later. I will add a caption to correct myself.

 

While I am here tho, I cant for the life of me figure out the alternate RAMCS protection layout -  in this early one I feature here it may be a little odd but it works electrically.  But in the later revisions,  from what I can trace of it,  it looks like the base of each BC183 is connected to pin 20 of each RAM IC instead of the collectors !!  The collectors are pulled to 5v by the line coming from Q5 instead ?  that makes no sense to me , how on earth can pin 20 of a 6264 drive the base of a tr??

 

Gonna need to dig out me old laptop with proteus on it and have a play with the layout!

 

 

 

Edited by MAGIK

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AHHHHHHHHHHHHHHH!  f+_k me !

 

AH I get it now,  its got an alternate leg pinout.

And with that little L another whole mystery is resolved!

I betya a million folks working on these are putting BC183s in by mistake!!

 

 

 

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Thing is tho Im sure I have the wrong transistors in my own board and it works just fine.  Still , handy to know !

Ok  so I can add a wee addition to my drawings then.

 

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Thanks for posting the vids and the information here MAGIK, very interesting.

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2 hours ago, MAGIK said:

Thing is tho Im sure I have the wrong transistors in my own board and it works just fine.  Still , handy to know !

Ok  so I can add a wee addition to my drawings then.

 

You obviously have not suffered ram corruption yet

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That must have took some doing,Quite clever if you ask me and sharing all the hard work with us all.Excellent

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This is my method, If i put the mouse pointer over the track it will show me where it goes, alternatively if I click on a line on the right (like A8) It shows me where it goes! quite useful when you want to meter tracks from A to B

 

 

Edited by Andrew96_

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 Majik thanks very much for sharing... 

Im a newbie at board repairs and I have a few questions. When you test u4 what do the hi and lo pulses you describe look like on a multimeter?

Are u4 u5 custom chips and is it viable to just bang new ones in if you can get them? (U6 too?) Can they be read and programmed onto blanks? 

Thanks mate

 

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