Technical_reference - 第24页

Technical Service Manual 24 Revision Dat e: August 2004 (FOR FUTURE USE) LA T CHED CONT ROL SSR A Cell has an over- tem peratur e condition with a rapid rise past s et point. The c ause m ay be a latched (failed in the “…

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.)

Technical Service Manual 25 Revision Date: August 2004

(FOR FUTURE USE)

OPEN CIRCUIT BREAKER

A Cell is indicating an under temperature condition where the temperature rises but does not reach

set point. The cause may be an open circuit breaker or conductor in the heater power circuit.

POSSIBLE CAUSES

When a circuit breaker opens, power is not supplied to the heater. The Cell temperature rise is probably thermal drift from

nearby cells caused by the Cell Fan motor recirculating air in the tunnel between the Top and Bottom Cells in the zone.

Check the Operating Screen for a heater receiving power at a high percentage rate. The opposite heater in the same

Zone probably is receiving extra power to compensate for the nonfunctioning heater. The nonfunctioning heater should

indicate almost 100% power and the opposite heater in the same Zone should indicate about 50% power (normal is 10%

to 30%).

Circuit breakers are identified as F1-B, F1-T to F12-B, F12-T. (-B = bottom, -T = top)

Reset the circuit breaker. Then, if:

1) The circuit breaker trips again, very likely there is a short to ground in the heater

conductors or the heater.

2) The circuit breaker does not trip again, but Cell temperature does not return to normal. Very likely there is

an “open” in the heater circuit or heater.

3) The circuit breaker does not trip, and Cell temperature returns to normal. Should the Circuit Breaker trip

again later, it might indicate an intermittent problem with the Circuit Breaker or the heater circuit.