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B. Control Board Check
Before replacing a control board that does not show a visible defect and that you
suspect is bad, always conduct the following check procedure. This procedure will help
you verify your diagnosis. Always choose a white (W) neutral wire to establish a good
neutral connection when checking high voltages.
Alarm Reset: If the control board is in alarm (beeping), press the "ALARM RESET"
button on the control board with power on. For alarm information, see
"II.D.3. LED Lights and Alarm Safeties Chart."
1) Check S3 dip switch settings to assure that they are in the factory default position. For
factory default settings, see "II.D.4.a) Default Dip Switch Settings."
2) Move the power switch to the "ON" position. If the "POWER OK" LED is on, the control
board voltage is good. If the "POWER OK" LED is off, check the control transformer
secondary circuit. Transformer output is 10VAC at 115VAC primary input. If the
secondary circuit has proper voltage (10VAC) and the "POWER OK" LED is off, the
control board is bad and must be replaced. See "V.J. Removal and Replacement of
Control Board."
If the secondary circuit does not have proper voltage, check the control transformer
primary circuit. Check the power switch to a white (W) neutral wire.
3) The "OUTPUT TEST" button provides a relay sequence test. Move the power switch to
the "ON" position. Next, press the "OUTPUT TEST" button. The control board cycles
through all relays in sequence. The correct LED lighting sequence is 3, 2, 1, 4, 5. Note
that the order of the LEDs from the outer edge of the board is 5, 4, 1, 2, 3. Components
(e.g., compressor) cycle during the test. Following the output test, the unit resumes
operation. If the LEDs do not light as described above, the control board is bad and
must be replaced. See "V.J. Removal and Replacement of Control Board."
4) Confirm K6 connector output voltage (5VDC). Check at the following K6 connector
locations: Pin #2 to pin #3 pink (P) wires (Clogged Filter Thermostat), pin #4 to pin
#5 light blue (LBU) wires (Door Switch), and pin #6 to pin #7 violet (V) wires (High
Pressure Switch).
5) Confirm proper output voltage (3.8VDC) at RED K4 connector (cabinet thermistor)
pin #1 to pin #2 gray (GY) wires and WHITE K3 connector (defrost thermistor) pin #1 to
pin #2 orange (O) wires.
6) As the unit cycles through the sequence of operation, check for 115VAC from
K1 connector pins to corresponding components and relays as needed.