LOR blue board triac or ??? issue

[rickharp]

on Channel 14, I cannot get the triac to shut off from a dim state with a high voltage sorce. So, before I replace the triac, I wanted to make sure it wasnt something else. In testing the voltages, I notices an irregularity in the 6 pin integrated circuits near the triacs and was wondering if it could be a problem.

the attached graphic is pretty clear. it shows inconsitant readings on the respective leads. Any help would be great. thanks.


Attached files

[-klb-]

Between the triac and the opto, you account for probably 98% of the hardware issues. But it is not always clear which of the two is the fault. Probably 80% are the triac rather than the opto, and there may be cases where both are bad.

But, I would think that a bad opto would most likely result in full on, or full off. It might also be capable of generating a 50% plus condition in the same way that the triac might, in that it may become a diode in one direction, while retaining the SCR behavior in the other. Any other partial output states sound more like a triac issue to me.

I believe in the all off state, one of the two active leads on output side of the triac should be following like voltage, and the other one should be off. But, a blown triac could easily result in the trigger lead being shorted to line voltage, and back feeding 120V to the opto output.

[rickharp]

ugh, that is a lot of information, but i am still confused. is the opto the 6 lead chip i point to.

and isn't the triac the last thing prior to going to supply power. so could a bad triac give the opto that voltage on that one pin.

I have spare triacs but not an opto.

bottom line what do you think i should try first. thanks

[Gary Levelius]

I would change the opto. I had one channel doing exactly what you described and it was the opto that fixed it. The opto is an LED and a photo-triac. Seems one half of that triac in the opto went bed, causing the problem you described.

-Gary-

[Max-Paul]

rickharp wrote:

ugh, that is a lot of information, but i am still confused. is the opto the 6 lead chip i point to.

and isn't the triac the last thing prior to going to supply power. so could a bad triac give the opto that voltage on that one pin.

I have spare triacs but not an opto.

bottom line what do you think i should try first. thanks

Yes the 6 lead device is the opto. And yes the Triac is the last thing and is connected to the buss that is hot 120VAC. Yes as anohter poster said, Triac can be leaking current back to the opto. If you have spare Triacs, and desoldering is a walk in a park to you. I would do the triac. But be prepared to get some Optos. Seems that the more recent poster thinks that this might be your problem like it was his recently..

[jldavis1969]

rickharp wrote:

on Channel 14, I cannot get the triac to shut off from a dim state with a high voltage sorce. So, before I replace the triac, I wanted to make sure it wasnt something else. In testing the voltages, I notices an irregularity in the 6 pin integrated circuits near the triacs and was wondering if it could be a problem.

the attached graphic is pretty clear. it shows inconsitant readings on the respective leads. Any help would be great. thanks.

See the white residue on the board around the traic. I believe that is a gassing flare from the triac. I would change the triac first.

[rickharp]

gosh, i don't recall seeing that. it may be a flash flare too. i'll look at the board tonight and advise. thanks

[LightORamaDan]

An easy test: Using a solder sucker remove the solder from one lead on the resistor that goes to the triac. Gently bend it out of the way so there is no contact. If things are still dim it is the triac. If the channel goes out it is the opto.

Dan

[rickharp]

Great, thanks Dan.

The flare on the picture is from the camera flash. Removing one lead from the resistor, provided the same dim results than when it was attached. i'll replace the triac. thanks for your help. i'll let you know if that works.