I'm not familiar with the way the cover is secured to this model, but you
should try to get a good look at the tape head.
If it's got oxide residue from the tape on it, it needs cleaned (and also
the rest of the tape path parts.. capstan, guides, pinch roller and erase
head).
It can be cleaned with a soft swab and alcohol.
If the symptoms persist after cleaning, the head might be worn to a point
where it no longer produces good recordings, and good tapes will have poor
sound quality.
Another possibility for poor sound reproduction could be old or low quality
tape.
A close inspection of the head might reveal a wavy-looking head face. On
badly worn heads, it's fairly clear to see a distinct undercut in the face
of the head.
The only way to recover good sound quality from a unit with a worn head is
to replace and properly align the head.
If the head's not worn, it's possible that the head alignment has changed,
but that's unlikely unless the tape transport has been damaged or tampered
with.
Cheers
WB
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