I have just finished up a resto on a Whirlwind that was working perfectly fine previously and am now having issues. I went into test by pressing advance and get the following errors.....

M Drop bottom 27
M Drop middle 28
M Drop top 29

Now, the issues that I am having are, the solenoid that raises the three center pop up targets is not working, also the solenoid which operates the lift ramp is not working and the solenoid that ejects the ball from the cellars is not working. I have found that the problem is the F4 fuse keeps blowing. Where would I begin to diagnose this issue?