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Technical Service Manual 23 Revision Dat e: August 2004 DC STAGE OF CONTROL SSR IS HOT A Cell is indicating an over tem per ature condition wi th the tem perature slowly (or rapidly ) rising past the set point. T his m a…

Technical Service Manual 22 Revision Date: August 2004

CELL FAN MOTOR MALFUNCTION

A Cell Fan Motor malfunction can produce the following symptoms:

1) A Cell slowly reaches setpoint.

2) Cold solder joints on the product.

CHECK: Rotation of the Motor can be confirmed by a visual check of the heat slinger fan mounted on the motor shaft

between the Motor and the Cell. During normal operation, the heat slinger fan turns counter clockwise as viewed from

the outside of the cell.

SYMPTOM # 1

A cell over temperature approximately 10

C during startup,

POSSIBLE CAUSES

With this symptom, some careful investigating is necessary to find the problem. If the blower motor malfunctions, the

heat at the T/C will not change much. There will not be any convection in that zone, creating the possibility of temperature

drift from an adjacent heat zone.

SYMPTOM # 2

A Cell slowly reaches setpoint.

POSSIBLE CAUSES

This condition may occur when the motor is non-functional and the oven is just starting up. If the motor is not blowing air,

the Zone will take longer to heat up and the temperature at the faulty Cell will not reach set point. The T/C in the faulty cell

will sense the Infrared radiation from the Heater Panel

SYMPTOM # 3

Cold solder joints on the product.

POSSIBLE CAUSES

Check for a group of fans not operating because of a tripped circuit breaker or because of an Inverter malfunction.

If cold solder joints on the product may be an indication of a faulty fan in just about any location in the oven. The heat

transfer in the oven works by air volume and velocity. If a fan is not operating, the T/C for that cell could still register the

approximate correct temperature because the heater panel has reached the temperature setpoint. The amount of

convection in that zone will be significantly lower than normal. Since the heat is transferred by air moving over the

components and joints of the product, smaller airflow produces less heat transfer.

The faulty fan could be anywhere in the oven because if the product is not up to the required temperature upon entering

the reflow zone, it will probably not be at the “reflow temperature” for the required time. (Cold solder joints can be

produced if the preheat is incorrect, the preflow temp is low, or the reflow temp is low)

Technical Service Manual 23 Revision Date: August 2004

DC STAGE OF CONTROL SSR IS HOT

A Cell is indicating an over temperature condition with the temperature slowly (or rapidly) rising

past the set point. This may be caused by the DC stage of the control SSR getting hot.

POSSIBLE CAUSES

The control SSR is mounted on a heat sink (the electrical back-panel) because the normal operation generates heat in

the SSR. If the SSR is not making a good thermal connection with the electrical back panel, it may get excessively hot

during normal operation. When the SSR gets too hot, the control side can "conduct" for as many as three extra AC

cycles. This little bit of additional power to the heater will cause a slow temperature rise. If the SSR is "conducting" more

than three cycles, the additional power will cause a more rapid temperature rise.

The solution is to replace the faulty SSR when it is located. Use an adequate amount of heat sink compound when

replacing the SSR.

HINT: Cool the SSRs in the electrical enclosure by blowing cool air on them with a fan.

If the cooling of the fan causes the symptom to go away, replace the bad SSR.

THERMOCOUPLE PROBLEM IN OPPOSITE CELL HEATER

Cell temperature slowly rises past the set point.

POSSIBLE CAUSES

This problem may be caused by a T/C (thermocouple) problem in the opposite Cell heater.

Visually monitor the power supplied to the “problem” Cell heater: This can be done by viewing the Percent Output line on

the oven monitor screen. This option must be enabled in Setup, Display Layout, for it to function. Another method it to

look at the appropriate LED on the SSR relay board and/or check the Percent Power Indicators in the Control Program

Operating Screen on the Oven Computer. If the SSR LED is not on, (indicating little or no power applied) then the T/C on

the opposite Cell heater may be defective. Shut down the oven and open the Circuit Breaker to the opposite Cell heater.

Restart the oven and watch for the ”problem” Cell temperature to stabilize at set point. If it does stabilize properly, then

the T/C in the opposite Cell heater is probably defective or has a loose connection.

(Refer to the “HEAT CELL ARRANGEMENT” illustration.)

EXAMPLE: If Cell 1T is over temperature, open the Circuit Breaker for Cell 1B heater. After restarting, if Cell 1T

stabilizes at set point, the problem may be the Cell 1B T/C.

EXPLANATION: If a T/C is defective, then the Controller interprets the low of T/C signal as a “cold Cell” and continues to

heat the Cell beyond set-point. The resulting excess heat is transferred to the opposite Cell and sensed by the T/C there,

causing a reduction of applied power to the opposite Cell heater. (The oven controller is “fooled” by the low t/c signal)

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.)