Teletype 43K001/AAA, Repair Manual

Page: 29 / 82

3.
43K001 RO KEYBOARD TROUBLESHOOTING
TROUBLESHOOTING GUIDE
QUESTION
1. Do any indicators fail to light?
2.
Is the test message printed while
the PRINTER TEST key is
depressed?
3. Does the TERM READY indicator
turn on and ALARM turn off when
the PRINTER TEST key is released
(cover closed and paper installed)?
4. Does the ALARM indicator turn
off (if on) and TERM READY
turn on when the RESET key is
depressed (cover closed and paper
installed)?
5. Does ALARM indicator light when
cover is opened?
6. Is -10 V or +5 V present on pin 3
of keyswitch in question?
6a.
Is +5 V present on circuit card cable
connection of keyswitch in question?
6b. Is +5 V present on the corresponding
connector pin at Pl 07?
7. Does pin 1 of PRINTER TEST key-
switch toggle from +5 V to 0 V when
keyswitch is depressed?
8. Is negative pulse present on MLA3-3
when PRINTER TEST key is
released?
9.
Does voltage on MLA3-3 toggle from
+5 V to 0 V when RESET key is
depressed and toggle from 0 V to
+5 V when RESET key is released?
10. With no keyswitch depressed, is
MLB4-10 and 12 at +5 V?
lOa. Is 0 V present on MLB4-l, 2, 3, 4,
5, 6, 7, and 15?
lOb. With MLA3-11 and
8 connected to
GND, are clock pulses present on
MLB2-5?
Note:
Printer may line feed when MLA3-11
and 8 are connected to GND.
YES
Go to 6.
Go to 3.
Go to 4.
Go to 5.
Go to 12.
Replace defective key-
switch.
Check for broken or open
circuit land to pin 3 of
keyswitch in question.
Check for open circuit in
cable.
Check cable for open cir-
cuit.
Go to 10.
Go to 10.
Go to lOb.
Replace MLB4.
Go to lOc.
----- ----
MANUAL 525, 2-15
NO
Go to 2.
Go to 7.
Go to 8.
Go to 9.
Go to 11.
If voltage is -12 V de
go to 6a.
Go to 6b.
Replace defective keyswitch.
Replace defective keyswitch.
Check START CONTROL
circuitry.
Check START CONTROL
circuitry.
Go to lOa.
Go to lOb.
Check CLOCK DIVIDER
circuitry.