Technical_reference - 第33页

Technical Service Manual 33 Revision Dat e: August 2004 THERM OCOUPLE CONNECT ION The oven is indicating what appears to be a random high tem perature due to a bad ther m ocouple connection. POSSIBLE CAUSES This conditio…

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.)

Technical Service Manual 34 Revision Date: August 2004

GROUNDING PROBLEMS

The oven is indicating what appear to be random high temperatures due to a grounding problem.

POSSIBLE CAUSES

Each T/C is grounded at the controller when it is properly connected. If there is a poor connection to ground at this point,

the T/C reading will be unreliable and will indicate random high temperatures.

Check the ground connection AT THE CONTROLLER. Make sure that it is correct.

Use an Ohmmeter to check the connections and refer to the oven prints to make sure that the connections are correct.

(The grounding problem is usually electrical noise on the ground or a faulty facility ground with high resistance. This can

result in the noise affecting the T/C reliability.

(FOR FUTURE USE)

EXTERNAL AIR FORCED INTO HEAT TUNNEL

The oven is exhibiting random low temperatures due to external air entering the oven tunnel.

POSSIBLE CAUSES

ICBs (inter cell baffles): If the ICBs are improperly adjusted, it allows air from outside to enter the oven tunnel, resulting in

random low temperatures (Refer to the chart of initial slot settings for the oven.)

EXTERNAL DISTURBANCES: The reflow process is also susceptible to external cold air and large airflow events outside

the oven. For instance, locating the oven next to a large loading dock area could cause this problem. The XPM Series

ovens are not very susceptible to external influences, but under the right circumstances, this is a possibility.

AIR LEAKS: Check for air leaks in the oven tunnel.

(External air forced into the Oven tunnel usually affects only the first 1 or 2 zones)