On 09/30/2017 06:58 AM, Tony Duell via cctalk wrote:
One of my tape drives has a set of equal-value resistors connected to
each of the read channels, the others ends of the resistors being brought
out to a testpoint. You connect a 'scope there and read a skewmaster
tape. The idea is that if the read transitions all occur at the same time
(no skew) you get a pefect step on the 'scope, if some are later than
others you get a staircase. You adjust the heads for the smallest
width of the stairs.
Yes, this is the classic NRZI skew adjust testpoint. The
resistors sum up the read data latches, that are set by
seeing a transition of either polarity on a data channel,
and reset by a one-shot that is set to about half a
character time.
You run a skew tape or a tape written with all ones. If you
see a square wave, all is good. If you see a slope on the
wave, adjust the skew adjust screws on the head mount to
make it as straight as possible.
Jon
