All diode tests should be done with the machine off
![thumb ^^^](http://www.aussiepinball.com.au/Smileys/classic/thumb.gif)
I'm thinking along the lines that there is either some sort of short between column 1-7 and column 8, but it would be difficult for column 1 - 7 to all be shorted to column 8.
Seems like a "logic" issue to me, as your test proves that the lamps in column 8 are switched on when the corresponding ROW is switched on.
During a normal game, are all the lamps in column 8 "on" ? I guess they would be
![Unsure !@#](http://www.aussiepinball.com.au/Smileys/classic/unsure.gif)