Resistor and triac failure - how to read

My wife brought home a flat iron, used for straightening hair, from a woman she works with. It would turn on, but not get hot. I opened it up and discovered that a resistor (one lead blown off the board) and a triac (case had a chunk missing) had failed. Questions: What would have had to happen to cause this? What likely failed first? Did the resistor fail, causing the triac to fail, or vice versa? The resistor is tiny, about 6mm x 3mm, and the 5 color bands are very hard to read. My DMM reads 1.2 Mohm. Is the reading from a failed resistor accurate enough to get a replacement? If you had a resistor that you couldn't read the color bands on, how would you replace it?

Thanks in advance.

Tim

Reply to
timinohio
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Vice versa.

I would guess. It's not hard to experiment on.

Reply to
Homer J Simpson

Thanks, Homer. How would I know if I have it right, other than the thing doesn't pop when I plug it in? What are the dangers of installing a resistor that is too big or too small?

Reply to
timinohio

  1. What is Ur system voltage and what wattage is mentioned on iron? 2. It seems that the triac is for heat regulation. In that case there should be 2-3 resistors and few capacitors and ONE inductor which has same shape as resistor also a diac and regulating pot. I think that what U are saying as resistor is an inductor and it is burnt out so showing 1.2 M ohm resistor. In this case the triac has failed first and the inductor opened after excessive current. But for that there must be some fault in heater otherwise this won't happen. So it will be better to check if heater resistance is ok or not ( try to apply low voltage from variac and increase it to some level if heater is bad it will show high current after after some heating). 3. There may be no triac but just diode which is converting voltage. In this case snubber ckt has failed and thus diode failed and that inductor failed subsequently. Momentary overvoltage may have caused this problem.
  2. There may be something else but we will know only when U give all details.
Reply to
psdayama

You have to puzzle out the circuit. Why does it need a SCR? To control the heat? Too high a value resistor and it won't get hot enough. You have to decide what is the correct amount of heat.

Reply to
Homer J Simpson

Your triac has suffered a severe overload, probably a shorted heater element, chuck it in the bin.

Reply to
cbarn24050

heater shorts, then triac shorts, then triac gate resistor gets blown by the mains voltage on it and finally the controller, if any, dies. The whole appliance is shot - just get rid of it. A new one will probably cost about the same as a new triac in retail prices.

Reply to
Frithiof Andreas Jensen

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