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Technical Service Manual 34 Revision Dat e: August 2004 GROUNDING PROBLEMS The oven is indicating what appear to be random high tem peratures due to a gr ounding problem . POSSIBLE CAUSES Each T /C is grounded at the con…

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)

Technical Service Manual 35 Revision Date: August 2004

RADICAL RECIPE CHANGE

SYMPTOMS 1 through 6

For all of the following symptoms:

1. Temperature =< 10 degrees above setpoint and stable

2. Temperature slow rise past set point

3. Temperature rapid rise past set point

4. Temperature rises but doesn’t reach set point

5. Temperature appears to stay cold

6. Temperature drops from set point

POSSIBLE CAUSES

A radical change in the running recipe can cause these symptoms. An example of a radical change would be switching

from a reflow recipe to a curing recipe or vice versa. If you are experiencing this problem and cannot work around it, call

the Vitronics-Soltec Field Service or Applications Support departments for assistance.

(FOR FUTURE USE)