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Open Head Detector for Arm Electronics Chip

IP.com Disclosure Number: IPCOM000119319D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Swart, DP: AUTHOR

Abstract

Described is how a simple window detector circuit is used to sense if the read head wires in a direct access storage device (DASD) hard disk drive have become broken. In a disk drive containing a number of heads, all heads can be tested by electronically 'selecting' each head in turn, while monitoring only a digital output.

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Open Head Detector for Arm Electronics Chip

      Described is how a simple window detector circuit is used
to sense if the read head wires in a direct access storage device
(DASD) hard disk drive have become broken.  In a disk drive
containing a number of heads, all heads can be tested by
electronically 'selecting' each head in turn, while monitoring only a
digital output.

      If the head element leads (see the figure) are properly
connected to preamplifier 2, transistors 8 and 9 conduct equal
currents.  A DC restore circuit (not shown) compares the voltages at
nodes 15 and 16, and adjusts the base voltages of transistors 8 and 9
until the voltages nodes is 15 and 16 differ by a small voltage (less
than 0.1 volt).

      However, when one of the wire bonds of read head element 1
becomes broken, all of the current sinked by current source 5 is
carried by resistor 11 and transistor 9. The DC restore circuit
cannot make transistor 8 conduct since its emitter is disconnected
from the head.  No current is carried by resistor 10.

      The resulting 'open head' voltage difference between nodes 15
and 16 is detected with a window detector circuit 20.

      Window detector 20 effectively compares the 'open head' voltage
between nodes 15 and 16 with the voltage drop across resistor 26.
Resistor 26 and current source 23 are designed such that the voltage
drop across resistor 26 somewhat smaller than the 'open head' voltage
between nodes 15 and 16.

    ...