Bad pia.

This board doesn't have a PIA.
Are you sure the coil has a diode installed with correct orientation ?

Yes your right no pia's, sorry.
Can't think anything else than wrong side diode.
Maybe Wrong diode (to low) because it works for a few times.

Press all ic's with a socket.
You hear them make a craking sound.
Some times thats the problem.

When you put in new coil, was the transistor changed at the same time?

First, calling the coil you're having problems with by name (ie "Garage Release coil") is much more helpful than only referring to it by the transistor it's hooked to (ie Q5). I had to pull out a manual just to see what coil you were even talking about.

Now, that said. Check the area around the garage assembly under the PF. This is for the garage release, and if I remember right, there's a paper (plastic?) shield there that can get old and come off (but that might have been on the Q6 upkick coil, I can't remember). If it does, the motion of the garage causes the coil lugs to come in contact with metal and it blows the transistor.

If you can't make a shield to replace the broken/missing one, you can also unsolder the coil wires and put plastic tubing over the connection points on the coil there to help keep them from shorting to metal.

If this doesn't work, post a clear hi-res (change the dropdown menu to high-res before dragging and dropping) picture of your garage assembly from a number of sides so we can see if something jumps out as wrong.

Also, make sure you have the final ROM release because there's a problem with the trough up-kicker on older roms where it can burn out the coil and make Q1 blow. Since it was blown before, it's likely you have an older ROM that needs to be updated. If you do have older code and do not update it, the trough coil and Q1 will eventually fail prematurely again. I've attached the service bulletin that addresses this.

NASCAR_sb166.pdf

It requires a SLOW BLOW (timed) fuse. Fast blow is wrong.

What transistor part number did you use to fix Q5?

Also, have you checked the wires on the coils for a short by following them back and seeing if there's any point where a screw or something penetrates the wire?

These aren't helpful answers for diagnosing your problem remotely.

What's the full number on the actual transistor you put in the machine? The part number for the transistor in the manual has been out of stock most places (all?) for a long time. You likely got a substitute (is it the RIGHT substitute?) or a fake (especially if you got it off ebay). That's why the ACTUAL number printed ON the transistor is important. What is it?