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Table 3-2. (Cont)
Failure Modes and Probable Causes
Symptoms
All bits fail as a function of
particular address bits
Maintenance of Memory Magnetic Core Stack
Probable Fault
1. X-Switch or Sink PAC
2. CM-003 PAC
3. X-drive line
4. PA-335 PAC
5.
X-Selection Diode
6.
Loose cable PAC or mis sing
address in put signal
CAUTION
Use extreme care when taking these measurements
to avoid damaging the matrix windings.
Under normal operating conditions, it is unlikely that troubles will occur within
the magnetic core stack.
However, continuit:r measurements of the sense and drive windings
will enable maintenance personnel to check core stack wiring.
Sense Windings. -- To check the memory sense windings perform the following:
a.
Turn off memory power.
Remove the Sense Amplifier PAC (CM-032 or
CM-033) associated with the sense windings to be checked.
b.
Place the ohmmeter leads across the sense winding inputs (SWXX+ and SWXX-)
to the Sense Amplifier PAC as determined from the logic diagram.
One sense winding links
4, 096 cores.
For 8, 192-word memories, two sense windings must be checked for continuity.
c.
Resistance readings should be approximately 10 ohms for all sense windings.
The resistance readings for all bits should agree
w~thin
±10%.
Drive Windings. -- To check the memory drive windings, perform the following:
a.
Turn off memory power.
Remove the CM-006 and CM-106 Selection Switch
PACs associated with the X- or Y-drive line to be checked.
This can be determined from
the logic diagrams and Tables 2 -2-1 and 2-2-2 by relating the bad address to a sink and
switch output for both the X- and Y-coordinates.
The drive winding connections to the
core stack are shown in Tables 2-3-2 and 2-3-3 (Section III of this volume) and the coding
drawing (refer to Volume III).
b.
Drive line resistance is a function of the core stack characteristics (number of
bits, type and gauge of wire, and core spacing).
The actual drive line connections are lo-
cated on the printed circuit board of the core stack planes.
The selection switch outputs are
isolated by a diode from each drive line so that the resistance reading of any drive line will
include a diode forward drop.
The Y-drive line resistance is the same for all size memories
3-7
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