Technical_reference - 第25页
Technical Service Manual 25 Revision Dat e: August 2004 (FOR FUTURE USE) OPEN CIRCUIT BREAKER A Cell is indicating an under tem per ature condition where the tem perature ris es but does not reac h set point. T he cause …
Technical Service Manual 24 Revision Date: August 2004
(FOR FUTURE USE)
LATCHED CONTROL SSR
A Cell has an over- temperature condition with a rapid rise past set point. The cause may be a latched
(failed in the “ON” condition) control SSR.
POSSIBLE CAUSES
If the LED on the SSR controller board is NOT on, but the heater is getting hotter, a failed SSR could be the cause. The
SSRs provide AC power (200 to 480V) to the heaters for short periods of time (cycles) determined by the Program and
the temperature sensed by the thermocouple.
When an SSR latches “ON”, the heater is turned on without any limiting control.
If this is the case, the SSR has failed and must be replaced. Remember to use enough heat sink compound when
replacing the SSR.
SHORT TO GROUND IN HEATER
A short in the heater should produce a slow temperature rise past set point. The temperature increase is a
result of the power leg that goes straight to the heater making a circuit to ground.
POSSIBLE CAUSES
The “short to ground” could be in the wires, heater’s ceramic blocks or the heater itself. The “short to ground” will have to
be isolated and repaired.
(If the short is in the heater or the terminal blocks, the heater panel will require replacement.)
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Technical Service Manual 25 Revision Date: August 2004
(FOR FUTURE USE)
OPEN CIRCUIT BREAKER
A Cell is indicating an under temperature condition where the temperature rises but does not reach
set point. The cause may be an open circuit breaker or conductor in the heater power circuit.
POSSIBLE CAUSES
When a circuit breaker opens, power is not supplied to the heater. The Cell temperature rise is probably thermal drift from
nearby cells caused by the Cell Fan motor recirculating air in the tunnel between the Top and Bottom Cells in the zone.
Check the Operating Screen for a heater receiving power at a high percentage rate. The opposite heater in the same
Zone probably is receiving extra power to compensate for the nonfunctioning heater. The nonfunctioning heater should
indicate almost 100% power and the opposite heater in the same Zone should indicate about 50% power (normal is 10%
to 30%).
Circuit breakers are identified as F1-B, F1-T to F12-B, F12-T. (-B = bottom, -T = top)
Reset the circuit breaker. Then, if:
1) The circuit breaker trips again, very likely there is a short to ground in the heater
conductors or the heater.
2) The circuit breaker does not trip again, but Cell temperature does not return to normal. Very likely there is
an “open” in the heater circuit or heater.
3) The circuit breaker does not trip, and Cell temperature returns to normal. Should the Circuit Breaker trip
again later, it might indicate an intermittent problem with the Circuit Breaker or the heater circuit.
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Technical Service Manual 26 Revision Date: August 2004
CONTROLLER FAILURE
SYMPTOM # 1
A Cell indicates an over temperature condition with the temperature rapidly rising past set point. The failure of a single
output on the controller is a possibility.
POSSIBLE CAUSES
If a single output on the controller fails with a short to ground, the heater will receive full power continuously. During
normal operation, the SSR receives a ground signal from the controller output, and it turns on the AC power to the heater.
Therefore, when the output shorts to ground, the heater is “ON” all of the time. If this condition occurs, the controller may
or may not be aware of the fault condition, but, could not do anything about it because the failed output was the only way
for the controller to control the heater. These symptoms indicate the need to replace a faulty controller.
HINT: To help isolate this problem, disable the suspect heater in the software and then watch the SSR board LED for
that heater. If the LED is on after the heater has been disabled, then the controller output may be faulty.
SYMPTOM # 2
A Cell indicates an under temperature problem in which the cell appears to stay cold.
This condition can be caused by a controller failure.
POSSIBLE CAUSES
This condition will only occur when starting the oven from a cold state. When/if a single output of the controller fails, it is
most likely to fail “open”. If this happens, the SSR (and its heater) will never be turned “ON”. The SSR requires a ground
signal to turn “ON” to supply AC power to the heater. Should there be a general controller failure, all outputs (and SSRs)
should be “OFF” and all the heaters should be cold. These symptoms indicate the need to replace a faulty controller.
HINT: To help isolate this problem, enable the suspect heater in the software and then watch the SSR board LED for that
heater. If the LED is never on after the heater has been enabled, then the controller may be faulty.
SYMPTOM # 3
A Cell indicates an under temperature condition where the temperature falls from set point.
POSSIBLE CAUSES
This condition can be a result of 1) a controller failure, 2) or loose SSR screws, 3) loose power wires to heater.
HINT: To help isolate this problem, enable the suspect heater in the software and then watch the SSR board LED for that
heater. If the LED is never on after the heater has been enabled, then the controller output is faulty.
NOTE: If the oven is operating and up to temperature, it may take some time for the cell to cool down enough to verify
the state of the output, SSR, and heater.
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