Pitou said:

I already checked all pins with an oscilloscope. Continuity is good. Signals seem to be on all pins except for 1,2,4 and 6 if I remember correctly. Again, I'm not sure what to expect on these lines.

As for schematics, yes I have them, I even did post them on post #12 of this thread if you want to take a look.

Click to expand...

I'm looking at the schematics, and pins 2 (MD7), 4 (MD5), and 6 (MD3) on the Mega II Chip are MD lines (memory data?). They head to the MDBus and to UI5, which is a 74HCT245 on pins 18,16,14 respectively. These pins are labeled "B".

From the 7HCT245, it goes to, well, that part is snipped. from the image. But the 245 looks like a buffer chip, so the lines goes across from a B-side to the A-side and is bi-directional.

From the B-Side pins 18, 16, and 14 goes to A-Side pins 2, 4, and 6 respectively.

If the A-side of the chip are address lines, then this area is likely to be the problem:

Lines from the Mega II to the 74HCT254

The 74HCT245 itself

The A-side of the 74HCT245 address (?) lines.