Thanks for the ideas guys! I chopped the resistor pack out and that didn't make any difference. I checked the resistance on the line manually, with power off, to +5 and 0V and it was a little different but nothing obviously wrong. So I bit the bullet and chopped out the soldered in RAM that was being used to do the test with and magically the problem went away! It must have been a problem with the WRITING of the data to the RAM (or the input holding the bus line high??). Now I have to fix all the bits that I broke and then see if it works in the pinball table... One more question... the processor is a 68k with an 8MHz crystal. The can I replace the 6264-90 RAM with a 6264-12 one? (I'm presuming the 12 is short for 120.) Thanks, Phillip Eaton If you ever want to (un)subscribe yourself with TTL, you can send mail to: <Majordomo@flippers.com> with the following command in the body of your email message: (un)subscribe techtoolslist or from another email account, besides xxx@yyy.com: (un)subscribe techtoolslist xxx@yyy.com