Any Electronics Gurus?

[Guest RemedyCNC]

My remote control ceiling fan quit today. Light is on high and will not turn off. I think I have narrowed it down to a triac powering the hot side of the light. I am rusty as to how it should ohm out with a meter. Anyone know?? Pin 1 to 2 is only about 2 ohms, while 1 to 3 and 2 to 3 have measurable resistance. Wondering if this is the problem. Help!!??

By the way, replacement is special order, one month out, at a cost of $83. Worth trying to repair, even if I end up roasting it.

[Guest Lester Weevils]

Hi Remedy. That might indicate a fried triac.

Thyristors, triacs and diacs

If the pinout of your triac is like that in section b--

Triac acts like a gated latching switch. The resistance between A1 and A2 would ordinarily be very high. Turned off. When the Gate is triggered, resistance between A1 and A2 would go low. Turned on. And it will stay low until the voltage across the terminals goes to zero.

Used in an AC light dimmer, the triac is triggered ON at some part of the AC cycle, 120 times per second. And it goes back OFF when the AC voltage crosses thru zero. For low-light, the triac is triggered ON late in the cycle, and for bright light the triac is triggered ON early in the cycle.

There is no guarantee that all triacs would have the same pinout, but if the A1 and A2 show low resistance when disconnected from the circuit board, it is probably fried.

[Guest RemedyCNC]

Looks like I have my answer. Now the search for one local. Found them on ebay but I hate to wait for shipment from China! Thanks for your help. I appreciate it.

[hardknox00001]

Try here for source

triac

[Guest Lester Weevils]

It probably is not a fancy or esoteric part, but dunno.

Radio Shack may have a replacement.

I haven't done electronics for a long time. If you have a readable part number on the triac, best case is that it is a common generic number.

If it is not a common generic number, electronics parts stores which specialized selling to repairmen and industry would often stock ECG parts. There was a big ECG parts cross-reference book, that would cross over thousands of obscure part numbers down into the few hundred parts in the typical ECG store stocking lineup. Those parts were a little more expensive than buying some generic part, but not too bad.

Chattanooga area used to have a lot of good parts stores, but dunno which ones if any are still in biz.

[Guest jackdm3]

If nothing around you, Bluff City Electronics in Memphis has most everything.

[hardknox00001]

If nothing around you, Bluff City Electronics in Memphis has most everything.

Ohhh yeahhhhh............I see your Bluff City and raise you Randolph and Rice in Nashville

[Guest jackdm3]

Weren't those the two bastards in "Trading Places"!?!

Yes. I know. "Randolph and Mortimer."

Edited September 8, 2010 by jackdm3

[Guest Lester Weevils]

Lightning or some other power surge might be responsible for the triac failure.

Another thing that will fry triacs is reactive loads-- Loads that have excessive capacitance or inductance. The easiest normal way would be to connect a triac dimmer to a compact flourescent bulb which contains an inductor. There are some other kind of lights, such as "rain lights" which are tight bright 12 volt spotlights behind a step-down transformer. Rain lights eat triacs and SCR's for lunch, even if you use the triac as a switch rather than a dimmer.

Or too big a load could hurt the part. Putting too-big wattage bulbs in the circuit.

Or sometimes they just die for no knowable reason.

Best case is that the triac is the only bad part in the circuit. It is possible that some other bad part in the circuit could have caused the triac to fail. Perhaps the capacitor that is often in series with the gate in the triggering circuit. It can go the other way too-- sometimes one part will fail which causes other parts to go bad.

Unless the part costs a lot of money, maybe buy 2. If just replacing the triac doesn't work (and the replacement fails), then you can go looking for other bad parts.

That is a common problem in switching power supplies or amplifiers. The obvious symptom is smoked power devices, but just replacing the power devices often is just sacrificing perfectly good parts because there is some 2 cent bad resistor, cap, or diode which is the real culprit. When the replacement parts are pretty expensive, it is worth checking all the parts pretty closely before spark-testing the repaired device.

Edited September 8, 2010 by Lester Weevils