OP

Quoted from Oldschool77:

Ok, latest update (sorry for the delay, been really busy)...
Here's everything i have confirmed is NOT the issue (I have a Rolelrgames now, so even though i don't have a logic probe, i feel like having a good system 11 to go by voltage wise, i can rule most of this out just by comparison)...
It is not the following...
Solder flecks on the back of the board
Ribbon Cable (brand new)
Display or Master display board (swapped with Rollergames, and the issues stayed with the Taxi)
Wiring from MPU to the display (checked continuity on all wires)
Power supply (rebuilt by me a while back, and all voltages are spot on)
My repairs (I know the issue didn't start until after my repairs, but i tried removing all 4 transistors and leaving them off the board this time, cleaned up the traces really well so i can visually see there is no shorting with any of the traces, verified that with a meter, put the board back in the game with all 4 transistors out, and no change)
Here's what i THINK it is...But i need someone to confirm I'm reading the schematics correctly please....
The segment in question is " d' " (lower display, bottom segment). Tracing it backwards from the display board it goes like this...
Pin 5 Jack 3 of display board to pin 5 Jack 3 of MPU
Pin 5 Jack 3 of MPU to pin 5 of SRC9
Pin 5 of SRC 9 to pin 13 of U51
And then that's where i don't know where to go next....
But i do know this....On SRC 9 the pins are all 4.7Kohm except pin 5 which is around 4.0 Kohm (new one on hand....not sure that's my issue, i feel like something upstream is pulling that pin down, not the SRC), this was done with J3 unplugged.
And when the game is on, and in display test with all segments lit, I'm getting around 1.9VDC on pin 13 of U51, the rest have 4.8'ish VDC.
So to me that says that i have a potential U51 issue....and i have a new one and socket on hand, but I'm not ready to start replacing it until i reach out to you guys a bit more to see if I'm on the right track here.
On a side note, during normal operations U51 in my Taxi is significantly hotter then the other chips, and significantly hotter then U51 in my Rollergames