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U6D
6522
TIMING CHART
U6D-PBO
U
10 ,s
CIRCUIT THEORY
UBB-OUT
L
Q22COLLECTOR
I-
TP1
Print Wire Coil Protection Circuits
. 1
500s
..1
When a print wire is fired, the output PBO on U6D goes "low". This triggers the 555 U8B. The output
pin 3 goes "high" for 500 microseconds. This turns on Q20, Q21, and Q22. The potential developed
at the collector of Q20 is used as
+
VCC for the open collector Hex/Inverters U58 and U6B. R39 should
be adjusted to obtain the 500 microsecond pulse.
10
2
8
Vcc
Triger
reset
Reset >—
6
I
CR28
TH
R39
i
20krz<
7
Cli
I
looopj
01
C9
470 p
OUT
U8B
555
+5V
+5V
t——
-,
R36
021'
3.9k
I
Q20
L
—
—
-
I
R35
Reset circuit
1k
3
TP1
022
R37 2.2 k
R23
3.9 k
DIS
cv
GND
Lc8
ii
14
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