Service manual

26 V
+26V
U5D
6532
PAO
81PF Holdl
PA4
61PMOI
PAS
7 (PM1)
11
U6D
6522
81PM21
3
PA6
PA7
IllPM31
9
1526 AND 4023 CIRCUIT THEORY
Pl Jl
1. 14
STEPPING
ORDER
2S 2S
F
A
0
0
R
B
W
2626
A
1
R
0
2
M
27 27
0
T
3
I
0
282
N
I
4
L _____ .J
PF Motor
MO
ON
OFF
OFF
ON
ON
COIL
M1
M2 M3
ON OFF
OFF
ON
ON OFF
OFF ON ON
OFF OFF ON
ON
OFF
OFF
NOTE: DURING REVERSE
TRANSMISSION. THE
CURRENT FLOW IS
STEPPED
IN REVERSE
ORDER -
4. 3. 2. 1. O.
Paper Feed Motor Circuit
The paper feed motor is a four phase stepper motor. Sequentially exciting two phases at a time causes
the motor to turn in step clockwise or counter clockwise. See timing chart above. Four outputs from
U6D,PA4-PA 7, activate the current amplifier transistors 013-016. Current flow through the emitter
collector junction of 013, through phase A coil, through the emitter collector junction of 017 via
the center tap motor coil excites phase A of the stepper motor. This occurs when the PA4 output
of U6D goes "low", U7B pin 4 goes "high", turning on 0 13. The PAO output of U5D must also be
"high", then U7B pin 2 is "low", and 0 17 is turned on. CR17 - CR21 suppress CEMF developed
by the stepper motor coils. This protects the current amps 013-016.
*WITH NO CR 17 - 21
COUNTER-
ELECTROMOTIVE
FORCE
APPROX. 100 V
*WITH
CR 17 -21
.---r-COUNTER-
L.
__ --"~ I ELECTROMOTIVE FORCE
_ _ APPROX. 50 V
26 V=!~~~~""
The stepper motor holds in position when the paper is not advancing. This occurs when a low value
current passes through
2 phases, producing opposing torques holding the motor in position. Phase
A and phase
0 are turned on, and 017 is switched off. Current flow is limited by the 470 ohm 5
watt resistor that is in parallel with 0 17.
11