On a Roller Derby, there are three lamps behind the backglass letters ABCD. When the feature is awarded, the lamps blow. With the game on and not running, I can replace the lamps and manually activate the Magic Screen Feature Unit and the lamps light and do not blow. But when the game is running and the feature is awarded, the lamps blow.

Ideas?

Thanks for all the ideas.

-- The lamps blow if they are 47s or 55s.
-- The Super Section lamps do not blow when tripped.
-- The lamp fuse does not blow.
-- The wiper fingers are correctly aligned on their rivets, and it is installed in the correct position.

Here is the reply I got from Jeff Lawton, similar to Otaku's response, which I think is correct. Am going to try this now and will report back.

"I suspect the 50 volt pulses to the step up coil are finding their way to the sockets of those three lamps. Probably a short on the unit. Lift the feed wire to the three sockets and put a test relay on the wire. Electrically cause the ABCD to advance. If the test relay pulses when the unit gets to the lighting position you will know there is a short on the unit. "

Well, wiggle the damn wires, Robert!

That turned out to be the solution. Some of the wires coming into the unit are frayed and were making contact where they should not have been, presumably causing the short that caused the lamps to blow. It's working for now -- I played a few games, turned machine off and on couple times, scored some winners, etc.

Thanks.

Yeah yeah yeah.... I know how to do it right. I just don't want to (I will, though.)

98% done.

1) Mixer 2 relay buzzes a little too much some of the time. An annoyance.
2) Maybe half the time, the game will tick off an additional credit, cycle, and potentially award odds and features when you shoot the first ball. Jeff suggested that this is due to a break-before-make SPDT switch that isn't breaking-before making. I think he said it was on the Control Unit, perhaps switch 3. But don't quote me on that....