[Techtoolslist] Logic levels question 6502A (Missile command)

[David Shoemaker]

I am trying to trouble shoot a board.  I am getting some odd responses
reading the roms.  I noticed that the address lines coming from the 6502
seem to be going high at 3.5 - 3.7 vdc.  I suspect this is causing some of
the ttl to not latch high.

 

This is checked through a meter using the fluke to read a particular address
on a loop and using my scope for the same and while running the game.

 

Is this a normal value?  I don't see any pull-ups on the address lines on
the schematic.

 

David