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Technical Service Manual 31 Revision Dat e: August 2004 PHA SE FA ILURE A Cell is indicating an under- tem perature condition in which the tem peratur e rises but does not reach set-point. An under voltage c ondition is …

Technical Service Manual 30 Revision Date: August 2004

(FOR FUTURE USE)

SHORTED THERMOCOUPLE

SYMPTOMS:

1) A Cell indicates an under temperature condition in which the temperature rises but does not reach set point.

2) A Cell indicates an under temperature condition in which the cell appears to stay cold. (The actual temperature

could be very high.)

3) A Cell indicates an under temperature condition. (The Cell temperature was operating at setpoint, but now has

dropped from setpoint.)

POSSIBLE CAUSES

A shorted Thermocouple is a possibility. When a T/C is shorted, the two T/C conductors touch each other (not

intentionally) somewhere between the controller and the T/C sensing tip. The temperature “sensing” occurs at the location

of the “short”, instead of the tip.

The thermocouple is intended to “sense” the temperature at the cell face, so when a T/C shorts, the “indicated

temperature” will be lower than the “actual temperature” at the cell face.

HINT: Check the percent power indicators.

One Cell in the Zone with the shorted T/C should be at 100% power and the opposite Cell should be at 0% power.

One cell will shut off (0%) because the shorted Cell (100%) is causing a high tunnel temperature because of

misinformation received from the shorted T/C.

HINT: When this under temperature condition exists, check all T/C terminations and connectors. A simple check for a

short: remove the T/C connector from the cell and check the percent power indicators to see if the Cell stops overdriving.

(An open T/C should read as 999

C.)

Technical Service Manual 31 Revision Date: August 2004

PHASE FAILURE

A Cell is indicating an under-temperature condition in which the temperature rises but does not reach

set-point. An under voltage condition is a possibility. The under voltage condition can occur when one

phase of the power drops out.

POSSIBLE CAUSES

At lower voltage, the heater will produce less heat. Check the voltage at the Circuit Breakers first. If supply power is O.K.,

then the problem is with the heater or heater conductors. On reduced voltage, the heater may not produce enough heat

to reach set point during start-up.

(Each heater is connected to two phases of the three-phase power)

HINT: Check the heater conductors where they pass through the metal tube on the top of the cell. Remove the heater

plate and check the conductors and connections inside the Cell at the heater’s terminal blocks. Missing a leg could mean

that the circuit breaker for the heater tripped, or it could be a bad connection on the heater panel itself at the terminal

blocks. It could also be a bad connection anywhere in the wiring from the relay board to the heater.

* This could cause both legs to be without power.

GENERAL OVEN FAILURE

There is an under temperature condition where the entire oven appears to stay cold. This condition

is probably the result of a major oven control failure.

POSSIBLE CAUSES

Some reasons for this type of failure might be:

1) The controller fails to activate any heaters. (The AI board may have failed)

2) The 3-phase power turns into single-phase power (loss of 1 power leg) and some heaters will not operate properly.

(Heaters are single phase and with the loss of one phase, depending on which phases supply power to them,

some would operate properly.)

3) The control transformer circuit breaker tripped producing a power loss to all 120 VAC devices

(K2 will de-energize and remove power from the heaters)

POWER LOSS TO HEATER

A Cell indicates an under temperature condition following a drop from set point. This might be a result

of power loss to a heater.

POSSIBLE CAUSES

When the power to a heater is taken away, the heater cannot maintain the heat level that it has attained. The result is the

heat level in that cell dropping from the set point to some lower value. This may also be the result of thermal drift to a

lower temperature section of the oven. If the temperature drop is showing up in a cell which is a boundary cell for a

temperature change, and the heater in one of the lower temperature cells stops working, the thermal drift from high to low

may show up as a drop from set-point in the (normally) higher temperature cell. One possible way to find this failure

would be to disable power to the suspect heater in the software and watch for no change in the symptom. If there is a

change in the symptom, then the heater in question may not be the one that failed.

Technical Service Manual 32 Revision Date: August 2004

CONVEYOR SPEED

Cold solder joints on the product may be caused by a problem with the conveyor speed.

POSSIBLE CAUSES

Conveyor Calibration: The conveyor speed must be set correctly to allow the optimum time for the product to stay in the

various heat zones. If the conveyor calibration is not correct, the product may be traveling faster than the indicated speed

and not be getting enough heat to reflow properly before leaving the oven.

Encoder Error: If the encoder assembly were returning incorrect values to the controller, the results would be the same as

the above “Conveyor Calibration” description.

Controller: If the controller is having a problem, it could be causing a conveyor problem.

If a conveyor speed problem is suspected as the reason for cold solder joints, refer to the conveyor system overview at

the beginning of this troubleshooting manual for other information and troubleshooting tips.

DIRTY CIRCUIT BOARD

The product has cold solder joints due to dirty circuit boards.

POSSIBLE CAUSES

The heat and flux in solder paste in the oven can overcome a limited amount of oxidation and contaminants.

If cold solder joints are being produced due to impurities on the boards and components, check the stock going into the

oven. The stock may need to be rotated sooner or pre-cleaned before soldering.

If the boards are not clean, raising the heat in the oven will probably not do much to resolve the problem.

OLD SOLDER PASTE

The product has cold solder joints due to old solder paste.

POSSIBLE CAUSES

This condition can not be "fixed" by raising the heat. Check and/or change the solder paste currently in use.

Check the date(s) on the solder paste to be certain that it has not passed the expiration date. Keep the supply of solder

paste rotated so that the oldest paste gets used first. USE FRESH SOLDER PASTE FOR BEST RESULTS

NOTE: the paste being on the board for too much time before the reflow process occurs can also cause this condition.