Unknown symbol on board 2

[bnmorgan]

Working on fixing a small 120v dimmer, and it has a fairly simple circuit, but there's a component I've never seen before.

I think it's some form of diode, but the symbol is like 2 diodes facing each other, IE ->|<- and the part is labeled "DB3"

I need to know how i'd check this component for function. The circuit is just a cap, the DB3, potentiometer, "j1" (transistor?) which I also don't know if i can check, and because of the arrangement of the board, I can't read the numbers on.

Suggestions?

Byron Morgan - Tupelo, Mississippi
1947 Mayline
SolidWorks 2012

 

[VEBill]

Google: diac

...fixing a small ($10) 120v dimmer...

Why? ;-)

 

[bnmorgan]

The dimmer is part of a much more expensive light fixture that I'm trying to fix for my boss. I'd be fine with buying a replacement dimmer if i could find one similarly small (.75 x 1.375") and adequate for a single 120v 35w halogen bulb is all it runs.

The diac symbol looks close (on wikipedia) although the sidac looks closer, except the triangles are both closed. I googled DB3 and it seems to be a "bidirectional trigger diode"...

working on drawing the thing. I'm not an EE obviously, so I'm slow.

Byron Morgan - Tupelo, Mississippi
1947 Mayline
SolidWorks 2012

 

[VEBill]

Google: light dimmer circuit

The many examples will help you to sort through the one you're dealing with. They're all mostly the same.

 

[VEBill]

"Google: light dimmer circuit"

PS: ...and then click on Google Images.

It's a gold mine.

 

[benta]

DIAC respectively SIDAC, both names are common.

The DB3 is from ST Microelectronics.

Cheers,

Benta

 

[bnmorgan]

Good grief.....a million ways to do the same thing!

Attached is the layout of what I have here. The potentiometer I'm not sure how to represent correctly. there are 2 terminals on bottom and 3 from the edge. The edge center and "high" side are used along with the 2 bottom. Sorry for the roughness of it. Wondering if I would be just as well to build one of these with the diac/triac on perfboard.

dimmer is mine

http://files.engineering.com/getfil...5-7592-45bd-80e5-7c7ae9dd6760&file=dimmer.jpg

lamp dimmer is one i might be able to build?

http://www.circuitstoday.com/wp-content/uploads/2008/02/lamp-dimmer.jpg

Byron Morgan - Tupelo, Mississippi
1947 Mayline
SolidWorks 2012

 

[VEBill]

Can you just replace the device that's failed? If you're not sure which has failed, then replace them shotgun style (all of them).

Probably not easy if it's the potentiometer.

 

[bnmorgan]

well, after more poking and prodding, it does seem to be the pot is shot. not getting any kind of proportional reading from the center to either wiper contact or between either of those on bottom and the wipers or center. Boss's suggestion was also "shotgun"

Gonna guess that the DB3 Diac isn't polarized, right?


Byron Morgan - Tupelo, Mississippi
1947 Mayline
SolidWorks 2012

 

[bnmorgan]

Well, now that i have removed all the components from the board, I find that it IS that diac/triac circuit I linked earlier, except with a resistor not in place (the board has a spot for it, and some of the values are different)

Triac bt134 600e
Diac db3 c502

The capacitor only has 333J and 400V on it, it's a dark orange part. What value would that be? 333uF?

Byron Morgan - Tupelo, Mississippi
1947 Mayline
SolidWorks 2012

 

[VEBill]

Diacs are symmetrical and are not polarized.

333uF @ 400v would be a physically very large capacitor. It's probably 33 x 10^3 pF = 33nf = 0.033uF (many orders of magnitude smaller than your guess).

 

[bnmorgan]

Well, I have been told why it stopped working: he plugged in a 12v 35w bulb (not 120v) and it smoked it instantly of course, but i don't know what else it hosed. The potentiometer is working fine after being disassembled and cleaned, but the rest of the circuit is still defunct. Am ordering all the other components and some new toys...errr...tools at the same time.

Thanks for all the help, and hopefully will have good news in a day or two (or next year)

Byron Morgan - Tupelo, Mississippi
1947 Mayline
SolidWorks 2012