I am going to replace the q15 transistor tommorow, cross my fingers. Then play some Skateball!

sometimes a Transistor measure correct in circuit, but it does not indicate that it is "good". I will is the least expensive and time consuming change you can do at this stage.

OK - The power supply board is giving me nightmares ! That's a "shocker" - literally !

Are you in a position to repair and upgrade the power supply ? Refer to Clay's bible -

http://www.pinrepair.com/bally/index1.htm#ps

If not, there are replacement boards available from our sponsors ;

http://www.rtbb.com.au/catalog/product_info.php?cPath=22_86&products_id=1128

Or near you part of the world ;

http://www.greatplainselectronics.com/proddetail.asp?prod=135-103

If you have the time, I'd be attending the Power Supply first, as it could potentially be the source of multiple issues.