Confused by the schematics...

[CheshireNoir]

Hey Folks,
I am trying to diagnose an issue with my Premium. It appears to be an 8501-3-04CR, and I'm trying to trace where the 20 pin connector marked X4 goes on the main board.
(This is the connector in the middle of the keyboard area.)
I've downloaded what I thought was the right Schematic from the archive. (8501_3_01_alpha_plus_motherboard_Xof2)
Unfortunately X4 on this schematic appears to be X7 on my PCB, and I can't find the appropriate connector. Am I using the wrong schematic?

I'm trying to plug a keyboard adaptor into the X4 connector, but it's not working so I want to check continuity to make sure I don't have a dead trace anywhere.

Cheers!

John

[MbeeTech]

Hi John,
Just as an FYI, The board revision is just the 8501-3 part.  The remainder of the part numbers you see relate to the 
revision of the layer they appear on.  For example, the 8501-3-04CR you see on the overlay means that it is 
revision (or release) 4 of the Component Reference layer.  Whereas the 8501-3-03C you see on the top copper layer
is release 3 [C]omponent side copper layer.  You will probably see a similar part on the bottom copper layer somewhere
that will most likely be 8501-3-03W (meaning release 3, [W]ire side).

There is essentially no difference in this area of the circuit between release 3 & 4, with the exception of IC4 pins 9 & 10 are swapped
which is of no consequence as both are inputs to the same 2 input OR gate.
The Schematic for release 4 is clearer though, and easier to follow :

   

Here is the pinout of the external keyboard connector for clarity:

   
Where pin 17 (STROBEn) connects to IC6, pin 11 (the external LPEN input),
pin 13 is the Column Output Enable that goes to pins 2 & 14 of IC7.

Here is the layout of the signals on the board (a screen shot taken from the keyboard 
replacement kits PCB, looking down from the top of the board)

   

[CheshireNoir]

Thanks Ewan,
That's absolutely brilliant! I'll break out my multimeter tonight and see if the fault I'm seeing is somewhere obvious.

Cheers!

John