488 MKII Audio Bus Issue

Discussion in 'TASCAM Analog Forum' started by baremountain, Nov 19, 2015.

  1. baremountain

    baremountain New Member

    Joined:
    Nov 2015
    Messages:
    3
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    0
    Gear:
    414, 424 MKII, 488 MKII
    I'm in a weird predicament (and it's kind of long-winded but it's that way for clarity's sake - please bear with me). I purchased a newly serviced Tascam 488 MKII off eBay at the beginning of September (with the 8-channel RCA output mod). It arrived & worked perfectly (by which I mean I was able to record on all 8 tracks, the motor speed was consistent, everything seemed to be in order).
    However, a couple of days ago I started working on my second album (the whole reason I bought the 488 - thought I'd forgo digital this time around), and while working on drums, I found that while input signal was both audible in headphones and visibly being ported to Track 3 on the visual monitor, upon playback the recorded sound was incredibly quiet, muddy and scratchy. Frustrated, I gave up for the day. I did some research yesterday and thought maybe it was an input problem, so I tried all the other inputs. While tracks 1, 2, 5, and 6 all can have audio recorded on them and faithfully played back at the same volume, tracks 3, 4, 7, and 8 do not have this ability - they all turn out to be scratchy and very quiet (unless the input signal is clipping the entire time - then you can kind of hear it). After about 3 dozen attempts to record on these tracks, I opened up the machine and disconnected & reconnected all wire clips but to no avail. I opened it back up again and decided that I'd test the Record/Play PCB (the top PCB located in the bottom shell beneath where the channel controls would go).
    To do so, I swapped out the channels as such: 1<->3, 2<->4, 5<->7, 6<->8. This means that audio read by the head for channel one was now being displayed and controlled by the slider for channel 3 and vice versa. I discovered that after the switch the same four channels (formerly 3,4,7,&8 and currently 1,2,5,&6) were now completely messed up - the erase head wouldn't function on them & no new sound could be recorded.
    I swapped the channels back to their original location (now 1 means 1 again) and played an 8-track recording I had made several weeks prior. I noticed that unless I ported channels 3, 4, 7, & 8 through the Group 1L/2R bus, they wouldn't play through the line output.
    So it's really starting to seem like a bus issue. My best guess is that the Group 3/4 bus isn't communicating with the record/playback head properly.

    Has anyone experienced a similar issue? I found this post on here describing a similar problem, but they said the Group 3/4 switch was not engaged on the channel strip in their case, but the Group 3/4 switches are definitely engaged on mine.
    I am not too well off financially & would like to do anything in my power to fix it myself, so any suggestions would be helpful. I have only minor knowledge of electronics and repairs, so please keep that in mind when responding with technical suggestions.
  2. stevezen

    stevezen New Member

    Joined:
    Oct 2015
    Messages:
    10
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    From:
    US
    Gear:
    DM24, DA20MkII, tape dks
    Sorry to hear of your problems; sadly, this sounds very similar to what a friend of mine went through whith his unit, and seems to be the case with bargains in seemingly good shape sold on ebay. My friend's unit starting misbehaving in much the say way almost a month after he bought it. He paid a low price up front, but to get it serviced far outstripped his ebay original cost. Good luck.