So far, all of the power in my IMSAI checks out OK. I've brought it up with the MPU-A installed and I get flashing lights. Press the STOP switch and I get solid lights. Now the weird part: When I toggle the address switches and press EXAMINE, here's what I get on the address lights: Legend: O - light off X - light on - - switch off ^ - switch on Lights OOOO OOOO OOOO OOOO Switches ---- ---- ---- ---- Lights OOOO OOOO XOOO OOOO Switches ---- ---- ---- ---^ Lights OOOO OOOO OXOO OOOO Switches ---- ---- ---- --^- Lights OOOO OOOO OOXO OOOO Switches ---- ---- ---- -^-- Lights OOOO OOOO OOOX OOOO Switches ---- ---- ---- ^--- Lights OOOO OOOO OOOO XOOO Switches ---- ---- ---^ ---- Lights OOOO OOOO OOOO OXOO Switches ---- ---- --^- ---- Lights OOOO OOOO OOOO OOXO Switches ---- ---- -^-- ---- Lights OOOO OOOO OOOO OOOO Switches ---- ---- ^--- ---- Lights XOOO OOOO OOOO OOOO Switches ---- ---^ ---- ---- Lights OXOO OOOO OOOO OOOO Switches ---- --^- ---- ---- Lights OOXO OOOO OOOO OOOO Switches ---- -^-- ---- ---- Lights OOOX OOOO OOOO OOOO Switches ---- ^--- ---- ---- Lights OOOO XOOO OOOO OOOO Switches ---^ ---- ---- ---- Lights OOOO OXOO OOOO OOOO Switches --^- ---- ---- ---- Lights OOOO OOXO OOOO OOOO Switches -^-- ---- ---- ---- Lights OOOO OOOO OOOO OOOO Switches ^--- ---- ---- ---- Lights XXXX XXXO XXXX XXXO Switches ^^^^ ^^^^ ^^^^ ^^^^ If I hit EXAMINE NEXT from the above state, I get: Lights XXXX XXXO XXXX XXXX And, if I hit EXAMINE NEXT again, I get: Lights XXXX XXXX OOOO OOOO So I think the lights are working. I think something is wired strange in the panel? Are there Z80 mods I should look for? Thanks, Bill