Hey Pin Folks,

Been tinkering with my system 1 machine (Totem) trying to debug a problem. Been reading a bunch of pages suggesting that it's good to test the switch matrix chips. I'm using a logic probe and trying to test 7404 and 7405 chips (see attachment). In my attachment you see referenced Z8, Z9, Z28. I'm guessing these are locations on the CPU board where the chips are located, but for the life of me I haven't been able to find a diagram of the board that shows these locations. What am I missing?

pin.jpg

Wow..thanks so much...why did all my scouring on the net not turn this up?

Furthermore...I have the original Totem instruction manual and it doesn't appear in there despite the fact that your attachment is labeled just like many in the book...very strange.

Thanks guys. Just did the testing that's spelled out in the "Switch Matrix Problems" I referenced above. Z8 seems to check out fine, but I'm just now testing Z9 and it seems that both pin pairs don't test high. One tests high and one low (input/output). I'm wondering if this indicates a problem with the chip. 7405 is an inverter, correct? As such wouldn't you expect it to test high on one pin and low on its neighbor since it's an inverter?

What might I be missing here?