Variations of the DSI (Direct Spark Ignition) board, below, are used on all Norcold refrigerators that have electronic controls. This circuit board not only provides a spark to the burner electrode to light the burner, but also opens the gas valve and provides the safety mechanism for cutting off the flow of propane if the burner goes out permanently or doesn't light. It also notifies the operator of the refrigerator if the burner fails to light.
The DSI board for the Norcold has changed a little over the years, in looks and in operation, but generally you can use a newer board to replace an older one, but not vice versa. Changes to the board involved the sensor connection and eventually its elimination.
We'll begin with the original board in describing how it works. When gas is the chosen heat source for operation, 12 volt power is supplied to the #1 terminal (+) and the #6 terminal (-) of the DSI board. This puts the board into operation, and high voltage is sent via the spark connection on the board to the ignition electrode at the burner which sparks to ground. At the same time as sparking begins at the electrode, 12 volt DC is sent to the gas valve solenoid through terminal #4 to open it, and low voltage DC is supplied to the sensor electrode through terminal #5. The #3 terminal is a normally closed circuit and initially has 12 volt power at the terminal. Once the sequence of operation as been established for the board, the circuit opens and power at the #3 terminal is discontinued. This is demonstrated by the check light on the control panel illuminating momentarily when the board first tries to light the burner. If the board fails to light the burner, it will go into lock out and energize the #3 terminal, causing the check light on the control panel to remain on. The DSI board will only try to light for 30 to 60 seconds (Trial for Ignition Period) before it quits and goes into lock out, cutting off power to the gas valve and not sparking. This is a safety feature.
Low voltage DC is supplied to the sensor electrode at the burner by the #5 terminal of the DSI board. (Note: the burner in the graphic above is only one style of burner; there are others) The low voltage circuit started by the #5 terminal is completed when the burner flame is ignited and current flows from the sensor electrode through the ionized flame to the ground of the refrigerator. This signals the DSI board that a flame is present, and sparking at the ignition electrode ceases. If the flame goes out, the sensor circuit is opened, the board is notified, and the Trial for Ignition Period begins again.
As the DSI board (or Ignition Control Module, as Norcold calls it) evolved, the sensor connection at the modular plug (#5) was moved to a separate wire internally connected to the board and running directly to the sensor electrode. This board works the same as the original board, and when it replaced an earlier version, one just had to connect the new wire to the sensor electrode and eliminate the old one.
The next evolution of the DSI board eliminated the sensor circuit all together. The ignition circuit and ignition electrode took over the job of the sensor circuit and sensor electrode. The ignition circuit was given the ability to monitor the flame by sensing the resistance between the ignition electrode and the burner. When there is no flame, the resistance is high between the electrode and burner. When a flame is present, the resistance drops between the electrode and burner, notifying the board that all is well.
Troubleshooting. First of all, if the DSI board appears to be working correctly, but the flame is not lighting, be sure there is no air in the line and the manual gas valve at the back of the refrigerator is not in the off position. Remember there is a Trial for Ignition Period, after which the board will go into lock out. If propane has not reached the burner in this amount of time, the board will do its job and shut down. Sometimes, if air is present in the propane system, you will have to turn the refrigerator off (for about 10 seconds) and back on to recycle the board's sequence of operation. You may have to do this several times to purge the air from the propane line.
If there is no spark at the burner, turn the refrigerator off and remove the spark wire from the spark connection on the DSI board. Restart the refrigerator, and if you hear the DSI board sparking internally, that part of the board is good and the problem probably lies with the ignition electrode. Don't try this test for too long a time, because the board also opens the gas valve. If there is no internal spark, check for 12 volt at the #1 terminal. Note: if the refrigerator thermostat is satisfied or off, the refrigerator will not try to light and there will be no power at the #1 terminal.
Inspect the ignition electrode for foreign debris fallen on it or for cracks. If anything grounds the electrode (including moisture), it will not spark. The gap between the electrode and burner should be about 3/16". If, after removing it from the electrode, the spark wire sparks to metal on the refrigerator but doesn't spark when re-connected to the electrode, the electrode is bad. Turn the manual gas valve off when performing this test so propane is not allowed to accumulate. Also, hold the spark wire with a pair of insulated pliers so you don't get shocked.
If there is a spark at the burner, but the gas solenoid doesn't open the gas valve, check for 12 volt across the solenoid terminals. If 12 volt is present and the valve doesn't open, the valve is bad. You can usually here the valve click open or "feel" it click open when placing your hand on it. If there is no 12 volt at the gas solenoid, check the modular plug at the DSI board for clean connections. You can also test the #4 terminal on the DSI board for 12 volt. If 12 volt is not present and everything else is working right, the board is bad.
On models with a sensor circuit, if the flame lights but drops out shortly afterward (during the Trial for Ignition Period), there may be a problem in the sensor circuit. Inspect the sensor electrode for damage or debris, and be sure it is in the flame. You can connect a milliampere meter in line between the sensor electrode and the sensor wire to measure the amperage. If you have less than 5 milliamperes, replace the electrode. If replacing the sensor electrode doesn't solve the problem, replace the board. Since the new DSI boards don't have a sensor circuit, replacing the board after replacing the sensor electrode will leave you with a useless part. You might want to gamble and just replace the DSI board.
You can perform a limited test on the DSI board when it is removed from the refrigerator, if you have 12 volt power, a test light, and three hands. Apply 12 volt to the #1 (+) and #6 (-) terminals. You should hear the board sparking internally. With a test light you can test the #3 and #4 terminals. Right after the board has been energized, the #3 terminal should have power momentarily then go out. The #4 terminal should have power constantly until the Trial for Ignition Period is over and the board goes into lock out. When the board is in lock out, there should be no power at the #4 terminal and should be power at the #3 terminal.