did you check that 3.3V line for ripple? check the cap filtering it? it has been a while since I did board repair so please excuse the email if it is way off base Art ----- Original Message ----- From: "David Shoemaker" <davids@oz.net> To: <rasterlist@vectorlist.org>; "'Technical Tools Mail List'" <techtoolslist@flippers.com> Sent: Saturday, November 05, 2011 2:33 PM Subject: [Techtoolslist] Logic levels question 6502A (Missile command)
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
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