Super bright broken lamp column

I have a Hyperball driver board that has a super bright lamp column that bakes the entire circuit, if any light in the column lights up, the entire column lights up, both the 8x8 and 8x4. So far, this is what I've done:

* Replaced the TIP42 in both columns, these are TIP42G from RS
* Replaced the 2N6548 with a CEN-U45 as the 2N6548 is an obsolete component
* Verified the resistors out of circuit
* Diode tested the 7408 and the PIA
* Disconnected the playfield, the circuit still bakes
* Buzzed all solder joints and their destinations
* My index finger have a 2nd degree burn from touching the resistors

What are the next steps here? I'm thinking getting new components for the entire circuit up to and including the 7408.

Thank you for your advice, I don't have a logic probe, will this one do?: http://www.frys.com/product/6508023

Got the probe! Pin 3 of the 7408 is dead (no pulse or pitch), this is the exit of the gate controlling my faulty column, traces from pin 3 are good. The PIA has low pulse on both the faulty and a working column. Is this expected? Thanks!