If you watch this and think you need to pay $120 for this board, it is just another example of a person ready to rip you off when none of that is needed. If the left (Supply) reel table turns when you are suppose to be playing a tape in the forward direction on a Tascam 122 Mk III or 112 MkII, but this reel has drive to the left, it is because through handling the deck you have sent a signal to the controller that said to go to reverse mode. The deck uses the same IC as is in the 112R Mk II so there is a reverse mode in it.
How to fix it without $120 of fancy circuits that are not needed? A dB25 connector and a tact switch or even a set of wires that you can short together. Me in the business built a dB25 with tact switch- you only use it to get the deck in the right mode again and then disconnect it and you won’t need it again. What he is doing with all those ICs I have no idea. With the dB25 which fit the remote connector on the rear of the deck is connect pin 24- Ground to Pin 1- Play mode. The deck goes into play with this one push the correct direction. Now disconnect the remote connector and the deck will work correctly after that- I know as I have done it. I service these all the time. dB25 are pretty cheap and most Technicians and Broadcast Engineers have them sitting around like I did. Don’t be tricked into $120 rip off.