BT139F triac lamp dimmer circuit
 

Jamie wrote:
ps56k wrote:
I have one of those tall halogen lamps with the internal dimmer knob.
It quit working...
Opened up and removed the slender dimmer board.
It has a BT139F triac, torroid, a couple of caps, the pot, etc
Tested a few points on the board - 120 AC - but nothing coming out.

If the traic is bad, what or where can I find a replacement ?

Did a search for BT139F and really didn't find anything besides
datasheets. tnx - Phil


http://www.datasheetcatalog.org/data...T139F-800G.pdf
there is the data sheet on it..
Test the Gate Voltage to low side of the load and make sure you are
getting a trigger voltage.
Normally, these units short and one or two things. They stay one
at full output meaning both thyristors are shorted or, you'll get an
effective dimming of 50% min with control up to 100%, this would
indicate one of the thyristors are shorted and the other isn't.
Getting nothing at all leads me to believe you may some other
problem.
You stated it has a torroid, I assume that maybe a pulse xformer
for the Gate circuit for isolation. You need to test if a pulse
on the input side( Primary) is actually there.

If the torroid isn't doing this job and then maybe it's a common
mode choke which is needed to remove the noise from the line. In this
case, you may have a DIAC component. This looks like a Diode but its
main purpose is to clamp to a short when input phase reaches a set
level, this clamping normally has a capacitor that generates a pulse
for the gate.
You must dig into it more to know..
Btw, this package you have is a Full Pack , fully insulated plastic..
you can replace it with just about any generic type TRIAC that meets
the Amps, Voltage and Trigger current that is close to the existing
component how ever, I would first dig deeper before assuming the
component to be bad.

And Btw, there is a Repair group you may want to ask those
questions in the future.
sci.electronics.repair

tnx for the info and other group - will followup there -

I'll dig a little more, and yeah... it's a classic choke.
Just had it apart on the living room floor with my VOM,
so I'll snip the wires and take it down to the bench.