IBM Selectric Reference Manual

If the machine will fail with only the R2A armature
attracted but wi II work with the T2 and R-5 arma-
tures I see Servi ce Hi nt 14.8. If nei ther test wi II
run 1 hand cycle through the operation and follow
the pri nt
area in output mode flow chart.
25.3 S. H. All ARMATURE TEST
Purpose: Check pri nt area for extra cyc les, caused
by magnet assembly fai lures.
Function Switch:
Print Space
Hit 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 ti It and rotate switches and the Hoover-
ometer handle to dynamically half-cycle whi Ie 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 Selectric I/O may cause ex-
treme Iy difficu It-to-diagnose malfunctions in liOn
Line
il
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 cyc ling 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 on Iy as a pre liminary 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 poi nt and N/C poi nt of contact assemb Iy. S low-
ly hand cyc Ie the machine and watch for a short indi-
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
IIbroken Up" signal rather than the clean, sharp rise
ti
me and stab Ie up leve I of a norma I contact signa I .
See Figure 19.
5·30
Bounce may be caused by insufficient tension on the
contact support straps, or by loose pile up screws in
the contact assemb Iy .
Di rty contact poi nts wi II a Iso cause much the same
indication on the scope as bounce. Contacts should
be cleaned with IB.M cleaning fluid and clean, lint-
free paper. Never use an abrasive cleaning tool on
Selectric contacts.
Contact bridging may show up under dynamic condi-
tions 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 IIfloatingll 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
IIfloat II 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 pi ck 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 Selectric. Scope across the two pins on the
epoxy block.

IBM Selectric Specifications

General

Type	Electric typewriter
Introduced	1961
Keyboard Layout	QWERTY
Carriage Return	Electric
Manufacturer	IBM
Printing Technology	Typeball (golf ball)
Power Source	AC Power
Power Supply	120V AC