Head alignment for legacy Sony FDD

Allison ajp166 at bellatlantic.net
Sat Jan 19 09:47:54 CST 2008

>Subject: Head alignment for legacy Sony FDD
>   From: "Peter" <pludikar at sympatico.ca>
>   Date: Sat, 19 Jan 2008 08:54:15 -0500
>     To: <cctech at classiccmp.org>
>I've been trying to create a working Sony MPF50W (as found in the HP1650B
>logic analyser) from 2 damaged units.  One unit had a fried board and the
>other unit had physically damaged heads.  I moved the heads and track 0
>sensor from the fried board to the other board and I need to do 2 things: a)
>confirm that the "new" heads are actually working and b) realign the track 0
>sensor.  I'm reasonably sure that the heads are okay, they show continuity
>on some of the pins, but I'm not 100% certain that is what I should be
>expecting.  I can't find any obvious sources of information on where to
>probe to see useful signals from the heads or find any procedure to align
>the sensor.  I have Tony Duel's diagrams of the HP9114 from hpmuseum.net .
>Any suggestions on where to find this information or how go about this would
>be really appreciated.
>Many thanks

Most heads have two sets of windings.  One for trim erase and a second
for read/write. The organization varies but the trim is two pins or 
have one pin in common with R/W and the RW is often a centertapped 
winding (three wires) so you should see three connections of near
zero ohms and a pair that are also near zero OR 4 pins that show 
near zero (common wire case).

The test for alignment usually requires a calibration disk and scope
but I've done it by doing reads of a known good disk and "finding 
the edges" and setting it for the middle.  Track 00 is usually less 
critical so if it happens when the head out and you can boot or read
the disk thats usually good enough.


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