Hi all I was working in the shop last night on a pac that has been giving me fits. I tried the "staring at it for hours" approach first, but that did nothing to fix it :-0 Weird symptoms. With a standard set up, I was getting a screen full of slashes and zeros, flipping every now and again. I replaced the vram with one of Clay's most excellent products, and the board now went through self test over and over. up to, but not including the cross hatch. Self test showed nothing. Removing the two middle roms changed nothing as well. (that was a clue). I tried a special daughter card I have that runs MS pac with no roms on row 6. booted to currupt screen images, so I felt there was a problem in adressing the roms, or ram. Last night, on a whim, I decided to try out my new HP 10592 logic comparitor. I set it up to check 8k becuase I noticed the IRQ was not firing. The comparitor said it was fine. Since it was my first crack at using the tool, I was not convinced. Going back to the adressing issue, I decided to check the ROM selct lines, by 7N chip, 74ls42. The comparitor showed 3 bad outputs on this. Swapped it and the board came to life. Even works with the original vram, so the bad chip could have been messing with the RD signal. No sound yet, but I'll get that working :-) On the Logic comparitor. The HP is a nice little unit, but you must get one with the zif card. This was an add on produced in later runs. It allows you to configure your chip with dip switches, where the original unit shipped with cards you had to phsically alter to match the chip characteristics. Others in the comunity feel he BUGTRAP device is a better comparitor, but I have no experience with it, so if you are looking for one, you should investigate those as well. The logic comparitor will be pretty much useless on any tri-stated device. It will not make a newbie a guru, and like any test equipment, you have to understand the it's limitations to use it effectively. Too bad I go sniped on that fluke model 90 z-80 thingy last friday :-( Gusee I'm going to have to save up for one of them nifty 9010A's Mike To UNSUBSCRIBE from techtoolslist, send a message with "UNSUBSCRIBE" in the message body to: techtoolslist-request@flippers.com. Please direct other questions, comments, or problems to jrr@flippers.com.