Question for any Sys 11 board gurus

[48]

Wondering if someone could answer a question about sys11 driver transistors?
This involves the Tip122's used to drive both solenoids and flashers via the ac relay.
Question is, if the 122 trans tests OK, then is it possible that the pre driver 4401 trans could fail and short,
thereby pulling the 122 permanently on?
I ask because I have one bank of four driven by IC 20 and 3 of those four 122's are stuck on.
Each of the 122's test OK, but I forgot (OK was too lazy!) to test the pre-drivers whilst I had the board out changing a couple of 122's.
Alternatively should I be looking at the 7408? 

[The pinballist formally known as Dean Morgan]

Sounds like IC 20 is stuffed

[48]

Sounds like IC 20 is stuffed

Bugger! Only say that because I don't have em on hand, and Jaycar don;t seem to have either.
Have ordered some but who knows how long they will take to get here.

Thanks for the help mate.

[48]

Just an update in case anyone else is researching later on....

IC 20 was stuffed (and gate device, gates stuck on, read high on output pins when not called for)
also, it had taken out U28, the 74LS374 before it, couldn't test U20 till I changed U28

Also of note, when I tested the 7408 with a DMM, it tested OK. Pays to use logic probe as well once the board is powered on the bench.