STERO SD3 Series, Service And Parts Manual

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5) Relay board relays K5-C, K8-C and K9-
C thru fuse F2.
NOTE: It is normal for the secondary voltage (output)
from transformer 2T to range between 11.5 to 16VAC.
C. 12VAC present to control board J1-1/3 from
secondary windings of transformer 2T.
Acceptable voltage is 11.5 - 16VAC.
1) Power supply on control board
converts AC voltage to 12VDC and
5VDC to power control board, display
and membrane switch.
2. ON key on membrane switch is pressed.
A. Control board enters self-test, also tests
display LEDs.
B. K5 coil on relay board energize.
1) EXT BSTR & VFC (AM) LED on relay
board turns on.
3. Self-test completes.
A. Machine type (AP, AH or AC) is displayed
followed by tank temperature.
B. MICRO LED on control board blinks at a 1
second on - 1 second off rate.
C. 5VDC present across 1QTM, 2QTM, 3QTM
and open contacts of 1FS.
D. Tank temperature is displayed.
E. Membrane switch - last selected cycle LED
is on. Cycle selection is enabled.
4. Door is shut.
A. Door interlock switch 1LS closes.
B. Control board senses float switch is open
and energizes fill/rinse solenoid 1SOL
through relay board. Tank begins to fill.
1) FILL LED on relay board turns on.
C. FILL icon and tank temperature are
displayed on display board.
NOTE: Once tank float switch is closed, a wash cycle
can be started by opening and closing the door even
though fill is not complete.
D. Tank float 1FS closes.
1) LOW LEVEL WATER LED on control
board turns on.
2) Control board energizes 3CON coil
through the relay board. 3CON
contacts close energizing booster
heater.
a. BOOSTER LED on relay board
turns on.
3) Control board signals relay board
(relay K9) to energize 2CON coil.
2CON contacts close energizing tank
heater.
a. TANK HEAT (AM) LED on relay
board turns on.
5. Depending on the fill time required to close float
switch 1FS, the control board will fill an additional
amount of time (75 - 120 seconds) after which
time the control board de-energizes the fill/rinse
solenoid 1SOL through the relay board.
A. FILL LED on relay board turns off.
NOTE: Tank Heat and Booster circuits remain
energized until set point has been reached; however,
a wash cycle may be started at any point.
6. Booster temperature reaches set-point.
A. Control board de-energizes 3CON coil
through the relay board. 3CON contacts
open de-energizing booster heater.
1) BOOSTER LED on relay board turns
off.
7. Tank temperature reaches set-point.
A. Control board de-energizes 2CON coil
through the relay board. 2CON contacts
open de-energizing tank heater.
1) TANK HEAT (AM) LED on relay board
turns off.
8. Door is opened and closed.
A. Control board senses that float switch 1FS
was closed before the door was closed and
energizes relay K8 on relay board. 1CON
contacts close energizing the pump motor
MTR. A wash cycle begins.
1) WASH LED on relay board turns on.
2) Machine line voltage present at
terminals DPS1 and DPS2.
9. Wash cycle.
A. The WASH icon and water temperature are
displayed.
B. Wash cycle continues for time selected.
C. Wash cycle completed.
1) Relay board K8 de-energizes. Wash
coil (1CON) de-energizes and pump
N.O. contacts open. Pump stops.
SD3 Series - ELECTRICAL OPERATION
F45576 (1015) Page 20 of 37