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Thread: partial erasure

  1. #1
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    partial erasure

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    hello

    ive come across a problem on another machine i recently ran into. this particular unit (otair 5050 8 track) seems to partially erase on tracks 1 and 3.

    where should i begin in trying to fix this? ive heard that i should begin by adjusting the head position THEN going to the erase bias?

    any thoughts? thank you

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    Quote Originally Posted by moogmymellotron View Post
    ive come across a problem on another machine i recently ran into. this particular unit (otair 5050 8 track) seems to partially erase on tracks 1 and 3.
    First, find out what circumstances this happens in. Record a long test tone on all 8 tracks, say 5 minutes or so, at 0vu.
    Then play it back a couple of times, just to make sure that there isn't something magnetized in the transport, or that it's not physical wear on the tape over those tracks, or crap on the heads or something.

    Next step - play back the whole five minutes and try recording each track in turn. Say, 30 seconds on track 1, then switch over to track 2, track 3 etc. Make sure you do these ONE AT A TIME - do NOT arm more than one track at once or you'll confuse the results.

    When you've recorded it, play it back and check the levels to see if anything unexpected is happening. If it was a straight misalignment I'd have expected it to affect all the tracks to some degree. I'd also expect an incomplete erasure of the actual, target track.

    After that, I'd suggest you try recording each track in turn, on a VIRGIN stretch of tape - not something that's ever been recorded on previously.
    Test each track in turn, and only that track. E.g 30 seconds of 0vu test tone on track 1, followed by 30 seconds on track 2 etc. Then, erase each one in turn and see if it works. If you have a residual signal afterwards, you may well have an alignment problem.

    If this doesn't make sense, let me know and I'll try and draw some diagrams :P

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    awesome nice!

    ive gone through several of those tests already BUT i have yet to test it on a virgin tape. One thing i noticed from the tape that ive been using however is that when i perform the same tests regarding playing/erasing on another machine, the tape fully erases. I was thinking that it mightve been an overused tape at first...

    im leaning towards an alignment issue since the heads are crystal clean and i demag daily. Id still would want to know how much of a chance could it be that perhaps the track bias is off? it records sound on sound and only attenuates the track down a bit, its still pretty loud and unusable.

    thanks again!

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    hi again

    currently aligning the erase head on the recorder.

    seems to be have more ghosts than i initially expected. Tracks 2 5 and 6 are recording and erasing perfectly. Tracks 1 3 and 4 record BUT residual signal is left behind on erase...basically unusable. Track 7 and 8 both have input, but nothing show sup on the meters much less records...hmmm

    id like to first get the partially erasing tracks good to go. im currently checking and setting bias on the machine...one thing id like to be sure on before i go on...how do i know if the erase head actually IS aligned. how do i know that the three tracks that do not erase dont have another internal problem outside of head alignment?

    id just like to make sure im not screwing up the bias on the track when its really a head issue or vice versa. any tips or tricks would greatly be appreciated!

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    the easiest thing to do in order to see if it's the erase head alignment causing the erase problem is to gently press on the tape over the erase head as you're attempting to record. if anything changes, it's a physical alignment issue.

    reading through your issues i doubt that's the case- poor erase head alignment typically affects all tracks, or just the edge tracks...not just one or two tracks.

    to prove this, take the a channel that isn't erasing and swap it with a channel that is erasing - my bet is the erase problem will follow the card.

    which means it's most likely an erase depth adjustment. i can't recall the 5050 erase adjustment procedure by memory...but there should be an erase adjustment somewhere on the card. erase peak adjustment is a lot like bias, there's a peak to it. sometimes over adjustment will result in poor erase too. just rock it back and forth a bit to see if anything changes- there could be an issue with the cards that can't be corrected with re-adjustment.

    -chris mara
    www.nobraineraudio.com
    www.welcometo1979.com

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    yea i aligned the erase head fairly well, atleast from what i can confirm, since three tracks record and erase perfectly.

    its been narrowed down to the bias adjustment...ive been trying to adjust to the manual specs...it gets better but refuses to erase completely. light traces are still being left behind. from what ive been read back on my meter is that its fine, however thats not the case. Are there tell tale signs if perhaps i overbiased? underbiased? im assuming now that stock specs are not going to be optimal for the unit and ill have to calibrate it to a new setting in order to get the machine to erase.

    what other faults could the machine have? im fairly certain the head is fine, and alignment is good. any help is greatly appreciated!

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    This is where an oscilloscope would come in handy. I'd take a look at the signal going to each erase head and make sure they were the same level.

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    yea im going to test the signal in the head tonight w my scope. the issue is definately in the cards, ive swapped them around and the problem follows.

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    Well it sounds like you're making progress.

    Something, somewhere in the bias circuit is not doing it's job properly.

    I'm not familiar with that particular machine. Do you know if it uses a single bias oscillator, or are there multiple?

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    it uses a single oscillator. i just searched the service manual and apparently each track has two bias adjustments for each track...i imagine perhaps adjust this second one will give me better results? ill be trying this soon, hopefully thats the case.

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