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Thread: Help calibrating a Sony TC-399

  1. #21
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    Also as a quick check, I tried recording over some pre recorded material. The erase head doesn't seem to be erasing as well as it should - I can still hear the original material on the tape albeit at a much lower level.

    Could be that the heads are not aligned to each other I suppose?

  2. #22
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    This is what the manual says with regard to adjusting the bias traps....... What am I measuring? DC volts? AC volts? I'm not too sure either where to place probes despite it telling me. Do I measure those caps separately or at the same time with some sort of spitter lead to my DMM's positive side?

    Where it says 'shield case' I presume that's ground yeah?

    screenshot-2019-08-25-13-00-44-png

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    Quote Originally Posted by Dan LB View Post
    This is what the manual says with regard to adjusting the bias traps....... What am I measuring? DC volts? AC volts? I'm not too sure either where to place probes despite it telling me. Do I measure those caps separately or at the same time with some sort of spitter lead to my DMM's positive side?

    Where it says 'shield case' I presume that's ground yeah?

    screenshot-2019-08-25-13-00-44-png
    You'd do better to poke that point with the scope, Clip the earth as close to the test point as you can find ground.
    Set the scope at minimum sensitivity and click the gain up steadily as the waveform decreases.

    The silicon transistor is two diode junctions. Bas/emitter and bas/collector. The B/E is forward biased by the bias resistors and thus there is always one diode's worth of voltage drop twixt base and emitter. 0.6-7 for Silicon, 0.2 for ye olde Geraniums.

    Dave.

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  5. #24
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    OK here's an update:

    I realigned the playback head using the 12kHz tone on the test tape - All good, getting a similar reading on the scope as before. The scope is jumping around a tiny bit (wow and flutter?) but is averaging a 45 degree line in X-Y mode.

    I then put on a blank tape and aligned the record head using a 12kHz tone from my iPad this time (my DAW output is 90deg out of phase at 12kHz!!! - I was actually outputting through an Allen & Heath Zed18 via USB so I have some troubleshooting to do there to find out if it's the desk or the ALT out from the desk or what! Need to make up some jack to phono leads to come directly from my Audient iD22). Anyway decent results (I think) aligning the record head albeit the scope was showing a bit of distortion and the 45deg line in X-Y mode wasn't exactly straight... had a very slight S curve to it... anything I can do about that? It's not there on the test tape, but then that was recorded on a pristine pro machine.

    More good news is that the machine is now erasing correctly too - it was a obviously a head alignment issue as opposed to a bias issue so I haven't touched the bias traps at all.


    Now on to playback and record levels!

  6. #25
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    To align the playback head you need to use a test tape.
    Then, to align the record head, you record a signal from a tone generator (iPad in my case) but monitor the recording from the playback head while it’s going to tape. Thus you are able to tweak the record head until it’s aligned with the playback head.

    So basically the heads require different methods to get them into alignment.

  7. #26
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    Finished the calibration today and the machine sounds great!

    Still have an issue with the pause lever but I'll look into that at a later date.

    Thanks for all your help Dave!

    I'll post some audio recorded on it when I get a chance.

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