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The thermocouple has gone bad. You will need to replace it to get the unit to operate again.
As this is such an old model I do not have any parts information in my database. Your local appliance parts retailer should be able to get the thermocouple for you. They are a common part even for a unit this old.
Please let me know if you require further assistance, or information. If not please click on "ACCEPT".Thank you.