Quoted from swampwiz:I need some advice on how to diagnose & fix a problem with Space Shuttle. The top hole either doesn't work or the ejection is too weak for the ball to get out. I did a resistance & inductance test on the coil, and it seemed to be OK. I have a Williams brand coil I could replace it with - and I suppose that I should just replace it just to take one possible failure mode out of the equation. But if I still have this problem, how should I try to diagnose a problem on the board? If it's a bad transistor or resistor, I could replace it, but I don't know what I am doing when trying to diagnose ICs, so I would just order up a new board (probably get a new MPU while I am at it).
I don't agree on replacing the CPU nor the driver board.
If you just have a coil problem I would concentrate on that.
As said before, you should be sure you don't have a mechanism problem, I had something similar on the ball launcher at out hole, a bit of WD40 on the mechanism and the problem was solved.
You may also have a bad transistor, replacing it is something easy, testing the resistor as well.
Nothing can be defective behind the darlington if you have just that coil problem so I would not waste your time checking the driver board ICs.
Check the coil and the mechanism first