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

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    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

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    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

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    From:
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    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
  4. Atul Giri

    Atul Giri New Member

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    Tascam Portastudio 414
    Hello guys. This is my first ever post on Tascamforums! I joined the forum in hope of finding a solution to a peculiar problem I'm facing with my recently acquired , a used Tascam Portastudio 414. The issue is similar to Rubin Hohlbein's panning problem. In my case, panning to the left works but turning the pan pot to the right on any channel basically lowers its volume. If I go all the way to the right it simply mutes the channel. It also doesn't let me direct audio to the right buss (R) to be recorded on any other channel as the manual suggests. This panning issue happens on all channels.

    For example, if I record something on channel 1 with the pan pot all the way to the left (as recommended in the manual) I cannot send the signal to right buss to be recorded on to channel 2 after recording something on channel 1, because panning hard right means muting channel 1. This is not sending any signal to channel 2 then. Same with channel 3 & 4. I have tried different combinations but the audio simply won't be directed to the R buss.

    When I try to record directly to any channel the audio comes only to the left monitor unless I press EFFECT2/Tape Cue and slowly turn the EFFECT 2/Tape Cue up to get a mono signal. This doesn't help with anything other than being able to listen to the recorded track in mono.

    I'm not that electronics-savvy and I don't know if it's an internal issue with the recorder or something that I don't understand. I followed the manual step-by-step still no luck. Any help or insight would be highly appreciated!

    Here's the manual. Please refer to page 16-20 for the method I'm following: https://www.manualslib.com/manual/263937/Tascam-414mkii-Portastudio.html?page=14#manual
  5. SkywaveTDR

    SkywaveTDR Well-Known Member

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    These kinds of problem require the action that would be done by a Technician or a person who can do the same. The buss problem will be there regardless of tape or Line input signal so most the time we put 1KHz in at -10dBV (316mV sine wave) and then go looking with a scope probe to find where the lack of signal is coming from. A service manual with clear schematics is needed to really determine the issue. Some units allow a sub in for the buss system and so that would be good to find out if the buss system is working then work back to the individual module. I was talking to the owner of Reel to Reel Heaven the other day and he said something about several good know technicians doing video about machines and their repairs- I don't know how quick the thing will happen. For the fast fix you would be required to send it to a Technician familiar with this unit to get it fixed faster. That is unless you have a scope and a Sine wave oscillator and some knowledge how to use them. Please note I am not drumming up business as I have too much already.
  6. Atul Giri

    Atul Giri New Member

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    Thank you @SkywaveTDR. Your insight is quite helpful. I'm looking for a technician who could look into it based on what you suggested. I totally understand and really appreciate your response!