Quote:
Originally Posted by ButchJames
The erasure problem has now been identified on my TC-645. Basically, it was the supply side tape guide setting. I strongly suspect someone in the past has been messing about with this? I have taken a shot of the setting; the blue spot identifies where the screw slot 'matches' its previous position - this gives me +- 180 degrees of 'play'. I've turned the screw just 60 degrees clockwise, and the erasure issues completely disappears. For now, this will do.
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The clue was in the erase head's abnormal wear pattern, visible in your photo in post #1 (reposted and highlighted to illustrate).
At first you made no mention of an erasure problem so I (we?) didnt pay much attention to the photo. (I was more concerned you might
create an erase problem by relapping a Ferrite head). After you mentioned an erase problem, I went back to your original photo to see if it was clear enough to show any misalignment in the wear pattern, which it did. At the lower edge it even shows both the correct and the incorrect wear lines (highlighted).
Erase heads sit on the same
centreline as record and play heads but are slightly wider, erasing into the guard bands.Your erase head would have missed erasing the top edge of the tape (track 1), but also the top edge of track 3.
This isnt a specifically Sony issue. The 1/4 track specifications were laid down in the 1950's.
As you have now discovered, the problem was solved by one simple adjustment of the tape guide.