Nintendo Vs. 1st pcb board repair question

Bravebluerx

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Hi Guys,

Got a logic probe, Vs. schematics that I am trying to learn how to read, and beginning to learn about pcb repair with repairing the main side of a Nintendo Vs. pcb MDS-04-CPU showing a blue blank screen, the sub side works fine.

I have spent some hours probing around and have noticed the programmed 2764 eprom I have set in position 2B on the board at pin 26 is not in a flashing state but looks like it is pulsing rapidly instead but not in a regular on and off pattern, it never goes off and looks and very irregular, When I place the eprom on the sub side of the board in position 8B, logic probe shows normal flashing activity at pin position 26 as this side runs the game fine.

I replaced the socket at 2B, but the probe still shows pin 26 irregular pulsing.

This is where I need some help, looking at the Vs. Schematic MDS-02CPU I can't understand where the 2B, pin 26 is connected to and if the numbers 25-30 outside chip 2F are representing that with pin 26 going into pin 12 of the ppu chip at 2F?

Thanks for any guidance!
 

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2B is a 2764 EPROM and according to that EPROM's pinout, pin 26 is not connected:
2764.png


The 25-30 outside 2F mean that those are the physical pin locations on that IC. So bit 13 of 2F's address bus (or A13) is on pin 25 of 2F. The "CA13 to CA8" labels are telling you that pins 25 to 30 from 2F are connecting to the CA bus.

So think of it this way:
"A12 of 2F come out on pin 26 of 2F and connects to CA12. CA12 routes over to A12 of 2B which is pin 2 of 2B. "

Nintendo goofed when they didn't put pin designations on 2D and 2A. ;)
 
Thank you for the explanation, are there any guides I could read that you recommend regarding schematics?

I've watched onecircuit's videos, now just realizing that is you :) haha, thanks for putting those videos together.

Looking forward to reading more about your recent missions trip as well!

-John
 
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