IBM 1620 Manual page 17

8.4v Ave
-'2..)67.3
*Use this diode as the reference diode because it is
closest to the calculated average.
** Th is diode may need to be rotated, the mask may
be dirty or out of adjustment, the gasket may be out
of place or the diode may need to be replaced if it
cannot be brought to specified levels.
5) With no tape in the machine, scope the refer-
ence diode selected in Step 4 and adjust the
.read lamp potentiometer until the diode output
is -lOv. Ideally, the potential on the read
lamp should not exceed llv.
6) Scope the remaining diodes and adjust the
individual read diode sensitivity potentio-
meters for a -lO.Ov output at each diode.
This is a starting point for the following
adjustments:
If -lOv cannot be obtained, it may be nec-
essary to change the read lamp potentiometer
adjustment, keeping in mind the ideal poten-
tial for the lamp. If the read lamp potentio-
meter is re-adjusted, the diode outputs should
be re-checked and the diode potentiometers
re-adjusted if necessary.
7) (a) Punch up a length of tape with 1, 2, 4,
8, C,
0, X,
EL, etc., in consecutive
positions. This can be done by inserting
a read alphameric instruction with the
typewriter designated as the input device
(3700501 00100). RELEASE and START.
Depress the sh ift key and type 1, 2, 4,
8, spare bar,
0, -,
+.
Nowsetupa
program loop to write alphamerically on
the punch (39 00500 00200 49 00000
00000). RELEASE and START. The paper
tape punch should now be punching the
desired pattern. Form the punched tape
into a loop and place on the read head.
A good spl ice can be made by cutting the
tape on an angle, about 45
0
;
holding the
ends of the tape, with Channell toward
you, overlap tape end in LEFT hand OVER
tape end in RIGHT hand by 1/16" to 1/8".
Glue in this position, with feed holes
aligned, using a quick setting glue such
as I BM tape muci lage, Part #221020.
(b) Set 1621 switch for strip mode.
3. 11
(c) Depress NON-PROCESS RUNOU T. The
loop should now be running over the read
head.
(d) Measure the peak-to-peak voltage swing
at the points given in Step 3. The diode
swing is a result of the change in light
when reading through tape (positive
level) to a light through a code hole
(negative level) and is a function of
diode sensitivity and tape transparency.
The diode potentiometers will adjust the
plus and minus levels up or down simul-
taneously.
r-
(1) The peak-to-peak voltage swing must
be at least 14.0 volts. If a diode
fails to meet the minimum 14.0 volts
swing with the power supplies at
their nominal values, and rotation
of the diode does not increase the
sensitivity thereby increasing the
swing, replace the diode.
(2) For diodes with peak-to-peak volt-
ages between 14.0 volts and 22.0
volts, center the voltage swing
about -1.0 volt reference with the
diode potentiometer. For example,
a diode with a minimum swing of
14.0 volts would be set to +6v and
-8 .Ov. See Figure 1.
+10.0
- " . . -
+ 5.5
"..
/
V
- 1.0
_ _ _ _ _ - 6.5
~
______
~~
__
~~
_______________ -12.0
Flattened Curve Indicates
Saturation (Above -11. 9v)
Proper Adjustment For
Diodes With Peak-To-
Peak Swing From 14.0v
To 22.Ov
Figure 1.
swing)
Diode Voltage Adjustment (14 to 22v