Teletype 43K001/AAA, Repair Manual

Page: 19 / 82

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QUESTION
23.
Is 560 KHz clock present on pin 1 of
MLB3?
24. Is depression pulse present on Sense
Amp input with keyswitch in question
depressed?
25. Is depression pulse present on
keyswitch logic input MLA5-10,
11 or 12 with key or one of the
keys in question depressed.
26. With REPT key and keyswitch
in question depressed, is serial
data on MLA5-2 present?
27. Does keyswitch in question meet the
mechanical requirements (depress and
release properly, latch, click, etc)?
------ ------ -- --
-
27a. Is depresssion pulse present on key-
switch logic MLA5-10, 11 or 12 with
no keys depressed?
27b. Is depression pulse present on Sense
Amp - logic inputs with no keys
depressed?
28.
Does keyswitch in question; REPT
left and right SHIFT, CAPS LOCK
or CTRL meet the mechanical
requirements (depress and release
properly, latch, click, etc)?
28a. With jumper strap connected from
pin 2 of keyswitch in question to
its associated sense amp input, is
failure corrected?
MANUAL 525, 2-5
YES
NO
Check clock generation Check cable for open
and driver circuitry.
circuit.
Go to 25.
Check visually for a short
between terminals of the key-
switch.
If there is no short visible,
remove the keyswitch
and check signal again at
input to sense amp .
If a depression signal
is
not
present, replace defective
sense amp.
If a depression signal is
present, replace defective
key switch.
Go to 26. Replace defective sense amp.
Check cable P107-6 Replace MLA5.
for continuity.
Check CR2 and CR4.
Go to 27a. Replace defective keyswitch.
Go to 27b.
Replace MLA5.
Check for open connect- Replace defective sense amp.
tion to keyswitch, ie,
depression pulse does
not appear at associated
keyswitch, pin 1.
Check for cold solder
connections at terminals
of keyswitch.
Replace keyswitch.
Go to 28a. Replace defective keyswitch.
Check for cold solder Go to 28b.
joint or broken land
from sense amp to key-
switch.
Replace keyswitch.