It could be any number of things. Assuming you're getting meter indication, I'd check your output connections 1st. Make certain your cable is still good. If so, apply a bit of pressure on that channel's jack to see if the internal connection is loose.
Tascam techs advised me to operate their machines horizontally to avoid the capstan motor bearing having to support the motor's weight. It also makes routine cleaning much easier.
It was TASCAM's 1st console. Performance was ok but nothing to get excited about. Its main selling point was how cheap it was compared to other consoles of the day.
It was TASCAM's 1st console.
The companion machines from TASCAM were from their 70 series. As far as I can recall, there were 2, 4, & 8 track versions.
If he wants to clear track space on the recorder, submixing to a buss (or 2 for stereo) and sending to an open track or tracks is the way to go. As I've mentioned several times before, the sync head has the same specs as the play head so there is no reason not to use it unless the new track is...
The MB-20 is a worth while unit but I strongly disagree about the Model 2 and 2A. Their performance is subpar and is very prone to outside interference.
I doubt using them makes any real difference. FYI - Operating a deck upright puts more wear on its motor bearings because they are supporting their own weight. Motors for TASCAM decks of are no longer available nor are the DC motors rebuildable.