Middleby Marshall PS570, PS360, PS200 Voltage Checks for Ignition Module and Combination Gas Valve

5.Burner Operation

a.Shut off the manual gas valve for oven. Turn the Burner and Heat switches ON. The spark should begin at the pilot burner within 30 seconds.

With the manual gas valve turned off, no gas will be present; so, the spark will continue for the lockout timing period of 90 seconds.

b.Turn the Heat switch OFF, then turn on the gas supply. Set the temperature controller set point above the actual oven temperature.

c.Turn the Heat switch ON. The system should start as follows:

•Spark turns on and pilot gas valve opens at once. Pilot burner ignites after gas reaches the pilot burner.

•Spark cuts off when pilot flame is established.

•Main gas valve opens and main burner lights after gas reaches the burner ports.

NOTE: Main burner flame may not be satisfactory until the gas input and combustion air have been adjusted.

6.Check Grounding

Electrical ground connections must be clean and tight. If the lead wire is damaged or deteriorated, use only No. 14 to 18 gauge, moisture-resistant thermoplastic insulated wire with a 221°F (105°C) minimum rating as a replacement.

Excessive temperature at the ceramic flame rod insu- lator can also permit electrical leakage to ground. Examine the flame rod and mounting bracket, and cor- rect if it is bent out of position. Replace the ignitor/ sensor if the insulator is cracked.

7.Ignition Module Flame Sensor Circuit Test

The ignition module provides AC power to the ignitor/ sensor which the pilot burner flame rectifies to direct current (DC). If the flame signal back to the control module is not at least 2.0 mA DC, the system will lock out.

The output of the flame sensing circuit cannot be checked directly, so check the flame sensing circuit indirectly by checking the flame sensing current form the ignitor/sensor to the control module as follows.

a.Connect a ampmeter or multimeter set to read DC microamps (mA) in series with the flame signal ground wire. Disconnect the ground wire at the control module. Connect the red (positive) lead of the meter to the free end of the ground wire. Con- nect the black (negative) meter lead to the ground terminal on the ignition module.

SECTION 3 - SERVICING COMPONENTS

b.Restart the system and read the meter. The flame sensor current must be at least 2.0 mA, and the reading must be steady. If the reading is below 2.0 mA or if the reading is unsteady, check the pilot flame and electrical connections as described above. Also, replace the ignitor/sensor if the ce- ramic insulator is cracked.

If the reading still is unsteady, it may be necessary to adjust the pilot pressure. Refer to Pilot Pres- sure under Servicing the Combination Valve on Page 98.

8.System Troubleshooting.

Start the system by setting the temperature controller above room temperature, and observe the system re- sponse.

Establish the type of system malfunction or deviation from normal operation by using the Intermittent Pilot System Troubleshooting Table on Page 103.

Use the table by following the questions in the boxes. If the condition is true (answers yes), go down to the next box. If the condition is not true (answers no), go to the box alongside.

Continue checking and answering conditions in each box until a problem and/or the repair is explained. Use the Component Checks section as necessary to per- form system checks.

After any maintenance or repair, the troubleshooting sequence should be repeated until the procedure ends with normal system operation.

Figure 75

Voltage Checks for Ignition Module and

Combination Gas Valve

Ignition Module
	Voltage
Test Points Marked	Fused	Nonfused
MV/PV to PV	3 VAC	24 VAC
MV/PV to MV	12 VAC	24 VAC
Combination Gas Valve
TR to TH	12 VAC	24 VAC
TH/TR to TR	3 VAC	24 VAC

NOTE: Information on the fused ignition module is provided for reference only. All ovens produced 1988 or later use the nonfused module. The fused module is no longer available.

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