I have a Whitewater that in lamp test, row 5 and row 6 light each other up both in test and while playing ie. 15+16, 25+26. 35+36 and so on for the entire row. I have done all the things in Clays guide - checked every diode associated with these lamps both for proper readings and orientation, pinged between J133,134,136 and J136,137,138 to find no shorts even tried here and there testing under the playfield altho most of these lights are on circuit boards. I also checked the Q85 (row 5) and Q86 (row 6) and they test fine but replaced them anyways. I also replaced the two diodes on the single lamp sockets (all others are on boards) The one weird thing not mentioned by Clay that happens in my machine is if you first turn it on and do lamp test, it doesn't immediately do it until the machine warms up? (10-20 sec maybe) and then does it consistently. Also, and this COULD be my imagination, but it seems that row 5 on first test doesn't trigger both but row 6 then triggers both and after that row 5 triggers both ie lamp test for 15 is just 15, then lamp test for 16 is 15+ 16 then after this do lamp 15 again and get 15+16. Hope that makes sense.

Any other ideas from the experts? Please? I figure this problem has to be easier than my Medusa  

Thanks in advance everybody
ME

start looking at changing the IC driving them ?

(can't seem to access pinrepair.com at the moment?)

To help isolate this problem I would start by disconnecting J133 (lamp rows - ground) and J137 (lamp columns - power). Then hook up a bulb and diode with some test leads to a specific pair of pins, say lamp 15. Now go to the single lamp test and see if this bulb lights up when choosing lamp 16. If the problem can be seen then you know it is on the driver board.

If not, then it must be downstream. A next test might be to disconnect the lamp boards under the playfield and see if the remaining single bulbs still show the problem. If not, plug them back in one at a time until the problem reappears.

Good luck!

HIDE is correct,find the ic that controls that colum or row on the CPU.
the 74LS24O DRIVER IC'S ON THE  CPU ARE USUALLY THE CULPRIT
LOCATIONS U11  U12  U13  U15

Thanks guys for all the ideas. After homework, basketball and skateboarding (the 9 yr old - not me ) I'll finally get some pinball quality time to fix it. Hopefully this weekend!

Thanks again
ME