My 50 year old reel to reel deck has given up all it's secrets and is now spinning along like it was built yesterday. Almost anyway. The motor fan is making a tiny bit of noise, so I will probably have to take the unit apart and adjust the spring holding it, but it is now playing tape perfectly at factory speeds.

Luckily my guess about the 1.5+0.5uF run capacitor seems to have been right, as the motor now spins absolutely silently with a replacement 2uF (400V rated) motor run capacitor. 

Luckily I caught another issue at the same time. The motor has some filters to prevent spikes when the motor turns on and off. Let's just say one of these pop filters have popped and I was lucky to get it replaced at the same time - I probably should've replaced both but time was running short. 

After I barely managed to fix the thing before going on holiday - not intending to bring a tape deck that weighs about the same as the rest of my luggage - I also managed to get some raw video of how it works together with my #ABN6502 SBC R1. 

I successfully managed to record and recover data from both my laptop(via external USB soundcard - had a hard time convincing my MacBook an external mic was plugged in) and the tape deck. 

Strangely I had worse luck when recording the video footage than when I did my first tests with the failing tape deck. My best guess so far is that I messed up the voltage divider values for the comparator reference voltage when I went from a LM339(quad) to an LM393(dual) - it should not be at exactly half VCC if I also bias the input at half VCC. Even if I have some hysteresis to prevent rail to rail noise, it won't have a defined state at reset.
I think I can solve that issue by replacing one of the 100k resistors in the ref voltage divider with a 120k - giving a zero crossing reference of 2.7 or 2.3V instead of 2.5V.  Either way it shouldn't hurt. 

My other guess is that the USB-C-hub I threw on my MacBook is noisy when combined with a USB-A external sound card. 

For now I'm happy with the design of the PCB itself - even if the resistor values are a bit off. You can expect all the schematics, gerbers, and Kicad files on Github very soon and a video about the whole thing on YouTube, soon-ish..