Technical_reference - 第32页

Technical Service Manual 32 Revision Dat e: August 2004 CONVEYO R SPEED Cold solder joints on the product m ay be caused by a problem with the convey or speed. POSSIBLE CAUSES Convey or Calibration: T he conveyor speed m…

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.

Technical Service Manual 33 Revision Date: August 2004

THERMOCOUPLE CONNECTION

The oven is indicating what appears to be a random high temperature due to a bad thermocouple

connection.

POSSIBLE CAUSES

This condition is an indicator error, because the actual temperature is probably acceptable. When a thermocouple gets

open in its conductor(s), it indicates the maximum possible temperature. It produces a higher indicated temperature than

expected. It is also possible to have the open exist for one sample time and not for the next sample time, thereby

producing a short indication of maximum temperature and then normal temperature immediately after. If the connection

is not open but simply high resistance, then the temperature indication could be higher than the actual temperature.

HINT: Check the connector(s) where the T/C plugs into the conductors on top of the cell and the terminations at the

controller.

CONVEYOR MOTOR NOISE

The oven is indicating random high temperatures due to conveyor motor noise.

POSSIBLE CAUSES

The conveyor motor is a DC motor with a set of brushes, which may emit a high, pitched audible noise. When the

brushes make this noise, they are also generating electrical noise, which can be transmitted to various parts of the oven

through the wiring. The T/C conductors are not shielded, so it is possible for the T/C conductors to pick up electrical

noise from nearby wires. The electrical noise on the T/C conductors can cause the system to indicate random high

temperatures.

If the conveyor motor is noisy, try replacing the motor brushes, the motor or shielding the T/C wire for its entire length in

the oven.

AC ON T/C or T/C WIRES

The oven is indicating random high temperatures due to an AC signal on the thermocouple or the

thermocouple wires.

POSSIBLE CAUSES

This is very similar to the conveyor motor noise problem.

THERMOCOUPLE / CONDUCTORS: The AC on the T/C or T/C wires is interpreted by the controller as a higher

temperature. Since the AC is not the normal signal, it is intermittent and random. The AC is closer to the controller than

the T/C so it shows up as a higher temperature than normal.

HINT: Disconnect the T/C at the controller (Jumper T/C terminals on controller) and check for the AC with an

oscilloscope. If it is still on the T/C wires, disconnect the T/C at the top of the cell to isolate the problem from the inside of

the cell or the wiring in the oven.

FRAME: Make sure that the AC is not on the oven frame. (Since the T/Cs are grounded, AC on the oven frame can

show up on the T/Cs.)