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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
 
H

Homer J Simpson

Jan 1, 1970
0
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?

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?

I would guess. It's not hard to experiment on.
 
Homer said:
Vice versa.


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

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?
 
P

psdayama

Jan 1, 1970
0
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

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.

4. There may be something else but we will know only when U give all
details.
 
H

Homer J Simpson

Jan 1, 1970
0
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?

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.
 
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

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

Frithiof Andreas Jensen

Jan 1, 1970
0
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?

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.
 
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