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4. With no keys pressed, the meter should indicate at least
2.5V. If
the
meter indicates 0.6V or lower, proceed to
step 7.
5. Press and hold one alphameric key. The meter should
indicate less than 0.6V. If the meter indicates 2.5V or
hi~er,
replace the keyboard assembly.
6. Press and hold two alphameric keys simultaneously.
The meter should indicate at least 2.5V. Proceed to
paragraph 5.1.4.3 if the preceding results are correct.
O.6V (or lower) with no keys pressed:
7. With meter leads attached
as
in steps 2 and 3, press two
alphameric keys simultaneously. If meter indicates
0.6V or lower, replace keyboard assembly.
8. Probe KB1 pins D,
E,
F, H, J, K,
L, M,
and N (bits 0-7
and Parity, Diagram 7-8) with no keys pressed.
9. Note bit configuration of encoded output. With logic
probe, a red indication is a 1 bit, and a green indication
is a 0 bit. With voltmeter, greater than 2.5V is a 1 bit,
and less than 0.6V is a 0 bit.
10. Find code in Diagram 6-5 or 6-6 that corresponds to bit
configuration observed in step 9.
11. Check center two lead frame terminals of suspected
module for 2.5V or higher. (Keyboard assembly must
be removed from bottom pan for this voltage check.
See paragraph 5.3.5.3.)
12. Replace defective module if 2.5V or higher is measured
on both center terminals in step 11.
13. If only one terminal measures 2.5V or higher and other
measures 0.6V or less, recheck steps 8 through 11.
If
same results are obtained, replace keyboard assembly.
14. Replace keyboard assembly if less than 0.6V is
measured in step 11.
5.1.4.3
Output Codes
The unshifted and shifted codes for a" keys on both type
keyboards can be checked by the following procedure,
which uses the logic probe and Diayram 6-5, 6-6, or 6-7.
1. Press and release desired key. Hold SHIFT (NUMERIC
on data entry keyboards) key down while pressing key if
desired character is on top half of keybutton.
2. Probe pins listed below with logic probe, and note bit
configuration observed. A red (UP} indication is a 1 bit,
and a green (DOWN) indication is a 0 bit.
Pin (lA 1-B2)
Keyboard Bit
S05
0
S08
S09
'}
S02
..,
oj
U05
4
M10
5
U09
6
M11
7
S13
Parity
5-6
3. Compare bit configuration observed in step 2 with
configuration for desired character shown in Diagram
6-5 or 6-6.
5.1.4.4 Shift Key Modules - Type A Keyboards Only
Two SHIFT keys and the shift LOCK key (NUMERIC and
NUM LOCK keys on data entry keyboards) generate an
input signal to the keyboard assembly encoder. The
encoder generates upshift character codes of the characters
appearing on the top half of the keyboard keys. The
following procedure isolates a shift module failure.
1. Set volt-ohmmeter selector switch to a position that will
accurately measure up to +5V dc.
2. Place minus (-) meter lead on KB 1 tab
X
(ground).
3. Check all
three shift keys individually for 2.5V
(minimum) on both center leads of the corresponding
key module when each key is pressed and for O.6V
(maximum) when key is restored.
4. Replace shift module that fails to generate proper levels
on both leads.
5. If shift module generates proper levels, and keyboard
generates incorrectly shifted characters (5.1.4.3), replace
keyboard assembly.
5. 1.4.5
Spacebar Assembly Mechanical Checks
The spacebar assembly and mountings should
be
checked
for easy motion and freedom from binds. The spacebar
should depress and return to the restored position without
drag or binds. Replace the spacebar assembly if binds,
broken mountings, or bent components are discovered. It
may not be necessary to replace the spacebar module
(actuator) if the problem is mechanical.
5.2 ADJUSTMENTS
Adjustment procedures for the IBM 3277 Display Station
should be performed after it is established that all operating
voltages are correct. Paragraph 5.1.3 details the voltage
checkout procedure.
5.2.1 Display Image Adjustments
A test pattern generated by the diagnostic program provides
the display image to
be
used during image adjustment. Test
Pattern 2 is used to adjust the Model 1 display image, and
Test Pattern 3 is used to adjust the Model 2 display image.
The procedure for displaying the required test pattern is
described in paragraph 2.2. If the program-generated test
pattern is not used, the test pattern image must be keyed in
from the keyboard. Diagrams 2-5 and 2-6 show Test
Patterns 2 and 3, respectively.
Adjustments should be performed in the sequence listed.
However, if only minor touchup adjustment is required,
analog card adjustments can be made separately. Use
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