Heathkit H9 - TROUBLESHOOTING WAVEFORMS

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Page41
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MISCELLANEOUS
PROBLEMS
CONDITION
POSSIBLE
CAUSE
63.
No
erase to end of line. 1.
Space
generator
on the keyboard
(special
character
generator).
1C404, 1C405, 1C406.
A1
:
0, A2= 1 for a
space.
2. Erase flip-flop is not
being set.
lC737D,
lC723A.
3. A write is not turning on the
space
(A2)
or enabling
RAM WE.
lc737 A, lC737
C,
lC7 17F, lC726A.
4. RAM counter
is
not counting up on erase. lC722C, lC737B.
64. No erase
page.
1.
Check the
items in
condition 63 above.
2. Erase filp-flop is not
being set by
lC715A.
65. Erase
continues
forever
(blank
screen).
2.
Erase
flip-flop lC723A is not
being cleared.
1C730
or
timing
signals.
66. No
scroll.
1.
Scroll
key not
pushed
in.
2.
Cursor/scroll coincidence
is
not being clocked
into lC709B.
rc733A,
lC733B, lC705C, lC710B.
3.
+12
or
+4
count
up not
being
clocked into
lC709A. lC735A,
tc735B. tC735D.
4.
Scroll
logic. lC7158, 1C739, lC733C, lC733D, lC741A,
tc741B, tc742c.
67. No erase
on scroll.
1. lC722A not
sefting erase
flip-flop.
2.
Gheck
the items in condition
64
above.
3. 1C724
(since
the
same
pin
ot
1C724 controls both the
scroll
count up and the scroll erase,
1C724 is
OK
if
either the scroll
count up or the scroll erase work).
68.
The
erased
line,
the erased block, or the cursor move to
the wrong
position
after a
scroll operation.
1. No
scroll count up.
1C506, 1C522.
2. No count
up scroll
+4/scroll +
12
signal
trom 1C724
(since
the
same
pin
ot 1C724 controls
both
the
scroll
count up
and
the
scroll
erase,
1C724 is
OK
if
eitherthescrollcount up orthescroll
erase work).
3. The 47 O resistor
between
plug
G
pin
5 and
plug
C
pin
5 on the
chassis
is missing.
69. Scrolls regardless
of
the
position
ol the Scroll
key. 1.
Scroll
key.
2.
Scroll
logic
(see
condition 66 above).
70.
No short form. 1. Short Form key.
2.
Counter controls.
1C724, lC73O.
3. Counter
multiplexers
on
the RAM
and
counter circuit board:
lC514A, lC514D
(+2O + +121.
lC530A, lC530D
(+'12+
+4).
4.
Check
+20
counter.
1C502, 1C509, lC510B, lC510C.
71 . No long form. 1.
Short
Form key.
2. Counter controls. 1C724,lC73O.
3. Counter
multiplexers
on
the RAM
and
counter circuit board:
lC514B,
lC514C
(+lQ
+
-4).
lC51 1A, lC511C
(+4
+
-'121.
4.
Check
+20
counter.
1C502, 1C509,
lC510B, lC510C.
No
auto carry.
1.
Auto Carry
key not
pushed
in.
2.
Counter controls.
1C724,lC73O.
3.
Counter not
counting
up:
No
carry output
trom
+4
(long
form) lC515B, lC530B.
No carry outpul
from
j-20
(short
form) lC510C.
Counter multiplexers
1C514, lC511A, lC51 lC, lC530A,
lc530D, rc528D.