Hello
I am checking out a Hitachi vt-m727 VCR which does not record sound
any more
Could be the eraser heads are not doing the job but since I also tried
recording on a brand new tape the fault could be elsewhere in the
circuit. I cleaned the eraser heads and they seem to be in order so I
suspect Q401 (as labelled on
schematics-http://www.geocities.com/anglomont/aud2.jpg on lower left )
What would you suggest ?(perhaps checking some condensator first..)
thanks in advance

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Hello
I am checking out a Hitachi vt-m727 VCR which does not record sound
any more
Could be the eraser heads are not doing the job but since I also tried
recording on a brand new tape the fault could be elsewhere in the
circuit. I cleaned the eraser heads and they seem to be in order so I
suspect Q401 (as labelled on
schematics-http://www.geocities.com/anglomont/aud2.jpg on lower left )
What would you suggest ?(perhaps checking some condensator first..)
thanks in advance


Were the eraser head faulty, you'd notice video probs as well on an old
tape -- the eraser head depolarizes across the width of the tape, hence you
lose audio, video and control tracks. The eraser head is, of course, moot
on a new tape as there was nothing there to erase.

First, using known-good prerecorded tape, confirm audio playback is also
gone. If so, read on. If not, we can rule out a lot of things.

Does it fail to record audio from all sources, including tuner?

If it's a hi-fi model, the same drum heads that are used for video also
handle the hi-fi audio, so a problem with the heads would show up in the
video as well. The audio/control/erase (ACE) head could be bad, but this is
less likely.

Check the simplest things first.
If your model has selectable audio dubbing/editing (via menu or front panel
switches), make sure you have it setup properly.
Some models will cut off the tuner audio when you connect external audio
input. Unplug all external audio input cables, if any.
If after doing the above it still won't record from tuner, suspect IC401
and/or associated support components. Check the voltages on IC401 pins. If
good, it's time for an o'scope and the rest of the service manual.

Hopefully, you haven't dinked around with any adjustments, such as the ACE
head, RT401, et al. If you have, the unit will require a realignment after
the actual repair.