Meanwhile, Back On The Workbench.....

 Well, it looks like I fixed the transport mechanism, finally. I carefully watched how it worked through my magnifying lamp, and learned a couple of things about how the idler tire (driven by the reel motor I rebuilt) engages the take-up reel for either Fast Forward, or Play/Record. I could see it slipping (?!!?), so I blasted that entire portion of the transport with some CRC QD Electronic Cleaner, blew it out with air, and the damn thing works OK now.

BUT.....and there's always a "But"....My preemptive strike on resoldering all the connections for the Source/Tape Monitor switch was a flop, as now the right channel is completely dead when in the "Tape" position. I ran my audio generator into the Line Input, and that section works like it should. SO.....I either missed a connection, or wound up with a solder bridge on the board, most likely caused by using too large a tip in my iron. I didn't even think to change the tip from the "Heathkit Size" down a bit to "Pioneer Size", and it may have bit me.

The offending group of connections are dead center in the picture. Yeah, I had to pull the bottom panel, and take all the screws out of the motherboard to push it away from the chassis so I can get at the little critters.

I'll also recheck all the wired connections to the board in case I broke one loose.

And yeah, I'll check to make sure it works BEFORE I bolt it all back together!