Safety; Scoping Procedures With Olsa - IBM Selectric Maintenance Manual

If the machine will fail with only the R2A armature
attracted but will work with the T2 and R-5 arma-
tures, see Service Hint 14.8. If neither test will
run, hand cycle through the operation and follow
the pri nt area in output mode flow chart.
-T5.3
S. H. ALL ARMATURE TEST
Purpose: Check print area for extra cyc les, caused
by magnet assemb Iy fai lures.
Function Switch: Print Space
nit and Rotate TO R-5
A fai lure wi II appear as a T3 R5 character (usua Ily a
"period") in place of a space. Check magnet assem-
bly adjustments, particularly armature knock-off and
trip lever to latch lever bite.
25.4 S.H. DYNAMIC HALF CYCLING
Use
0
LSA fi It and rotate switches and the Hoover-
ometer handle to dynamically half-cycle while check-
ing detent and alignment adjustments., On keyboard-
less machines, this is a more dependable method than
hand selecting the print magnet armatures.
25.5 S. H. CONTACT FAI LURES
Contact fai lures in the Se lectri c I/O may cause ex-
. tremely difficult-to-diagnose malfunctions in "On
Line" applications but will not be detected by OLSA
circuitry.
It is of the utmost importance that contacts be cor-
rectly timed, in proper adjustment, clean, and bounce
free.
Contact timing can be checked with a meter whi Ie
hand cycling the machine. Tests have shown that con-
tacts timed under hand power show little or no change
when later checked dynamically.
Contact bridging* can also be checked with a meter
but this can be regarded only as a preliminary check.
*Bridging -- Operating point makes contact with.
normally open point before it breaks contact with
normally closed point.
When checking for bridging, it may be necessary
to remove contact wiring to eliminate back cir-
cuits.
To check for bridging, connect meter leads between
N/O point and N/C point of contact assembly. Slow-
ly hand cyc Ie the machi ne and watch for a short i ndi-
cation on the meter. Check N/O air gap and N/C
contact rise if a bridging condition is indicated.
Contact bounce must be checked dynamically with a
scope. Bounce is seen on the scope as a "noisy" or
"broken up" signal rather than the clean, sharp rise
time and stable up level of a normal contact signal.
See Figure 19.
4-30
Bounce may be caused by insufficient tension on the
contact support straps, or by loose pi Ie up screws in
the contact assemb Iy.
Dirty contact points wi II also cause much the same
indication on the scope as bounce. Contacts should
be cleaned with IBM cleaning fluid and clean, lint-
free paper. Never use an abrasive cleaning tool on
Selectric contacts.
Contact bridging may show up under dynamic condi-
ti ons and appears as noise just after make time and
just before break time.
26.0 SAFETY
Sound safety regulations require that all electronic
equipment must be provided with a chassis ground and
that this chassis ground must be returned to earth
ground through the third (green) wire of the AC line
cord.
IBM safety regulations forbid any deviation from the
above and, therefore, the practice of "floating" the
scope must not be employed.
o
LSA's power supply has been designed so that its
reference point {or chassis ground} can be determined
by the needs of the user. This eliminates any need to
"float" a scope.
27.0 SCOPING PROCEDURES WITH OLSA
Magnet Pick Time
Condition 1 -- Print Select Magnets
Internally wired in OLSA are 47 Q resistors in series
with the print select magnets. It is the voltage grop
across these resistors that wi II show print magnet char-
acteristics on the scope.
With machines using
+
polarity, put the scope probe in
the magnet common jack and the ground lead in the
print magnet test jack (Tl, R-5, CK, etc.)
With machines using - polarity, put the scope probe
in the print magnet test jack and the ground lead in
the magnet common jack.
The scope wave form then wi II a Iways appear as a
signal starting at ground and rising to a positive level.
Condition 2 -- All Other Selectric I/O Magnets
To scope any other magnet, it is required that a 47
ohm resistor be temporari Iy wired in series with the
magnet pick coi I.
NOTE: A tool wi II be made available shortly to
provide this feature. .
This device can be kept with the OLSA. To use, re-
move the magnet pick coi I wire from its edge connec-
tor in the Selectric. Clip this wire to the alligator
clip attached to the resistor. Insert the pin connector
on the other side of the resistor into the edge connec-
tor on the Se lectri c. Scope across the two pi ns on the
epoxy block.