I've been working on a Black Knight driver board, and Q27 keeps failing, or so I thought. With the transistor removed, resistance from the collector to ground is 17K, while all the others in the string is >95K. I've verified that on other driver boards I have, the resistance for Q27 collector to ground is >95K. Because of this "low" resistance, the multi ball eject solenoid stays energized.

The board is not burned, but it appears the board is a little brownish under Q27, especially between the collector and emitter pads. I suspect this area is the source of my low resistance to ground. Has anyone had an issue like this, and what did you do to fix it? I hate the idea of drilling out circuit board between the pads, since its such a small area, but I don't see any other option.

Another thought was to cut the traces from Q27, select an unused driver transistor such as Q37, Q39, or Q41, and run jumpers to replace Q27 with one of those. Problem with that is now I have a "customized" driver board that is not compatible with anything else. Future techs would have no idea what was going on.

So, if anyone has had a problem like this before, what did you do to fix it? I'm open to ideas. Thanks

Here's a few pics - I've already tried the alcohol route. On the pictures with a light on the other side of the board, its more obvious of the burned area.

IMG_3027[1] (resized).JPG

IMG_3028[1] (resized).JPG

IMG_3024[1] (resized).JPG

IMG_3022[1] (resized).JPG

SOLVED - I put a meter across the connectors to monitor resistance as I scraped between the emitter and collector solder pads. I used a dental pick (very sharp - I punctured my finger while doing something stupid) and slowly scraped away. With each scrape, the resistance was increasing - I stopped scraping when I got to 100K of resistance. I did not have to dig very deep - I think the issue was just below the surface.

When you look closely, you can see the valley between the pads, but for the most part, I doubt anyone would notice. I am guessing that someone before me changed the transistor, and burned the board. I got this machine as a project, so I had no information concerning its history. I kept changing the transistor because of the low resistance reading, so I probably added to the problem. Regardless, I think BK is ready to fight again!