Tascam 644 Channel and Tape Head problems

Discussion in 'TASCAM Analog Forum' started by Andre Veloso, Dec 30, 2020.

  1. Andre Veloso

    Andre Veloso New Member

    Dec 2020
    644, DR-40
    Hi From Brazil!

    I just recently bought a 644 Midistudio Tascam. It is mostily working, but for 2 problems:

    1 - Channel 3 is working, but is not sending level information for the display - none of the inputs is showing level: mic, line level or tape playback. But is is sending signal for the tape recording head and all of the outputs. I swapped the channel 3 board with channel 1 board and now the channel 1 input on the display is not showing signal . So the problem is contained in the channel 3 board itself. Analysing the schematics I understood that the IC TC9164N is resposable for the eletronic switching and for sending the level signal to be interpreted by the display circuit. So my guess is something wrong with this IC or some component down the signal path.

    2 - Channel 3 on the tape head is not sending a aceptable output on tape playback - the signal lacks high frequency information (only bass and mids are present). I swapped the channe 3 input cable coming from the tape head with channel 4 on the rec/play board and the behaviour is the same: the cable with the channel 4 signal inserted on the channel 3 input is giving an OK signal level and channel 3 inserted on the channel 4 have the same bad signal than before, lacking highs. So the channel 3 on the Rec/play board is OK and something is happening in the tape head, on channel 3 only.

    I did some researches and some sugested to demagnetize the tape head (I still do not have a demagnetizer...)

    Tape head are not worn and the almost invisible tape head gap seems to be the same width on all channels.

    Any Sugestions for these 2 problems?

    Thank you very much guys for the attention!!
  2. SkywaveTDR

    SkywaveTDR Well-Known Member

    Feb 2014
    Chicago area
    Teac, Tascam, Sony
    Forget the demagnetizing as that will do nothing and is rarely if ever required- it is one of the snake oil ideas.
    Most likely you have some broken solder joints on interconnecting cables connectors or buss PCB lines. You need to go in to the unit and take care of all bad solder joints. The matter is even worse on portable type devices as they get moved around and bounced around like they were built to military type standards but they are surely NOT.