Hey Tony G, no worries, thanks for checking in.
Although I've had to take a few unrelated sidetracks recently, I have discovered something that I didn't notice before. Not sure how I could miss it. At any rate, I've discovered that when I jumper pin #2 into the circuit, (see the photo I posted a few comments ago for the connector), The 5.4 V rail indicator LED goes out! Or at least very dim. Something is pulling that rail down when pin 2 is connected. I simply didn't notice that before. So, I've been walking the dog along the schematic path looking for potential culprits. This means that every surface in my shop is covered in schematic diagrams! I can't use a lack of documentation as an excuse, that's for sure! Anyway, pins 1,2 and 3 on this connector are all originate from the 5.4 V rail, but only #2 causes this. The next stop on the path for pin #2's signal appears to be an IC labeled "DEMUX" on the schematic, which I guess is a de-modulator. There's also a diode straight to circuit ground in the path too, and I'm currently hunting that one down to test it since it just seems more unlikely that it would be an IC problem. Then again, I'm really green when it comes to the digital world.
So, that's where I am. I'll locate and test the low hanging fruit on this signal path and report back with any news. Thanks for your interest! I'll be struttin' around like Richard Pryor and Gene Wilder if I do get this beast working, and I really appreciate everyone weighing in. Best regards,
JRH