Tascam 414 mk1 Left Buss

Discussion in 'TASCAM DIY Repairs and Mods' started by Rubin Hohlbein, Feb 22, 2021.

  1. Rubin Hohlbein

    Rubin Hohlbein New Member

    Joined:
    Feb 2021
    Messages:
    2
    Likes:
    0
    From:
    Boston, MA
    Gear:
    Tascam 414
    Hi Friends. I am trying my best to refurbish my old Portastudio 414. Everything is working great at this point except something is wrong with the left side.
    I've checked the headphone out, line out, and monitor out--the Left side is silent in all of them. If I pan all tracks to the left, there is nothing coming out.
    I am thinking there is something wrong either with the left side of the master fader or some op amps on the signal path post-panning... I'm not really sure how to isolate the problem just from looking at schematics/block-diagrams. Can anyone with more knowledge lend me a hand?

    Thanks in advanced!
    -Rubin
  2. SkywaveTDR

    SkywaveTDR Well-Known Member

    Joined:
    Feb 2014
    Messages:
    648
    Likes:
    122
    From:
    Chicago area
    Gear:
    Teac, Tascam, Sony
    IF left line out is missing then the tape section does not enter in and a -10dBv Sine wave input into a line in will be traced all the way through the deck to the Line out. A oscilloscope is normally employed in a case like this as you want to see the progress of the signal and where it stops. Around where it stops will be the problem. If several of the inputs have lost the left buss then the problem is not in one input but a Buss section and the Master Fader can be checked with a scope pretty fast- they do fill up with fuzz and dirt that is what we have found. People do not cover these with a plastic sheet or a towel when not in use so carpet fibers and bug carcasses and other airborne particles get into to these. If the deck has a Bass in the -10dBV sine wave can be input there as then that allows the checking of the Buss amplifier itself.
  3. Rubin Hohlbein

    Rubin Hohlbein New Member

    Joined:
    Feb 2021
    Messages:
    2
    Likes:
    0
    From:
    Boston, MA
    Gear:
    Tascam 414
    Thank you SKYWAVE! I've checked the pins on the master fader and they appear to have a good connection. I am not sure how to identify the specific Buss amplifier, but I am fairly sure that this is where the problem is