You have to overdub and monitor off the sync head. There is no reason whatso ever that anything should be out of sync when you use either the repro or synec head.. unless some tracks are not switching.

:D Old analog geezer here, and former tascam fan. disable any record ready switches.

Test the sync of all good tracks placed in the sync position, they should line right up, just won't sound as clean, except for your bum track, don't listen to that one. Now, you recorded tracks, and you want to cut another track (overdub) in sync. All the tracks that you want to monitor need to be in the sync position. Do not listen to any track on the repro head at this point. You monitor your new track along with the tracks on the sync head. Which in reality is working as a record and play head. It is playing your existing tracks, and recording your new track in line with the others. The record ready switch should be set only for the new track(s) you want to lay down.

The only other causes, if you are doing what I said, is bad reed switches as a possible, or your heads were wired incorrectly. Another possible is your monitor mix is bleeding track(s) NOT selected for sync into the input of the new track.

Some boards do not have dedicated tape returns, so setting up your mixer, you have to be careful not to monitor the wrong source.

A dedicated tape in provides a seperate monitor section for off tape.

If you don't have this, you must use a pre-fader send from that track on the board to your monitor mix out, or phones. On recording boards this called a cue track. Otherwise, you may send other tracks to the bus that don't belong there.

Sorry for the long reply.

--Rick

long replys are AOK

This is good info. I will check into these possibilities. It may very well be that I have some wierd double monitoring issue going on. I didn't think of that.

Thanks,
Collin