Black Knight: Short Circuit Induced Fault - MAACA ARCHIVES - JOIN THE NEW FORUM AT HTTP://WWW.MAACA.ORG

Hello all!

While adjusting the fingers for the switch on the top bumper of a Black Knight machine, my father accidentally shorted the metal bending tool to what he believes was one of the posts of the bumper solenoid. The machine was turned on (no need to -remind- us about the importance of turning off a machine, we knew before and we know more now). We didn't think anything of it at the exact moment, because nothing really happened, so we can't say exactly which wires got shorted. But, we did short something, and the scent of burnt electronics drifted through: we knew something bad happened.

We turned it on, and visually inspected the boards. There was nothing that seemed visibly burnt or damaged: all ICs were fine, no bubbling/discoloration, no burnt resistors or caps or anything we could see on the surface. We powered on the machine, and here are the issues:

1) The two clusters of drop targets up top do not register points, nor does the bumper. (As a result, it won't trigger the solenoids).
2) On machine startup, 2220 points are instantly recorded on the machine, and the drop targets blink as though one of the targets were dropped (the count down to knock down all three).

My thoughts are that these switches are stuck ON in the mind of the CPU, and for that reason, on boot-up it counts the points, but won't count them again because the switches aren't seen as being released. I think it thinks that the switches are being held down.

We followed the wires of the color that we thought we shorted, and it led us to the CD4049UBE chips, two of them, which are the front lines for these switches. We figured that, if we shorted a switch line with a solenoid, we may have fried one of or both of these chips. I've replaced those two chips with brand new ones, and it didn't change anything: same symptoms, no new ones.

Would anyone be able to tell us what parts of the board are responsible for these switches, or even better, if someone has seen a similar problem before and knows how to fix it?

Thanks a lot!

Dan