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Thread: Looking for understanding on the SSR section of the Renard boards

  1. #1
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    Default Looking for understanding on the SSR section of the Renard boards

    I looking to understand what could be the cause/reasoning behind this. I've recently been replacing some old triacs with newer ones that work better with LED's and while testing a controller (XMUS) i found a bad channel. It was stuck fully on so I figured I must have overheated the triac.
    After replacing the triac again, the channel was still stuck on. So, I remember reading in the forums somewhere to try replacing the associated resistor.
    The resistor in question had no visual signs of being an issue and all solder joints looked fine. I'm about 98% sure this channel was not an issue before.

    So, replacing the resistor fixed the issue.

    But, I don't understand how a "bad" resistor could cause the triac to trigger. If I'm not mistaken, without the opto being triggered, there shouldn't be any current running through that part of the circuit, so how would it trigger the triac?

    Thanks in advance for any insights.
    Chris
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    Default Re: Looking for understanding on the SSR section of the Renard boards

    Hard to say. If the triac was stuck on and changing the resistor fixed it, my suspicion would be that there was some surface contamination (dirt or some sort of grease, maybe) on the board that was allowing enough current flow to turn on the triac. The physical and thermal actions of replacing the resistor removed or altered the surface contamination. Just a conjecture.
    Phil

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    Default Re: Looking for understanding on the SSR section of the Renard boards

    Thanks Phil, I guess that must have been it, it just seems weird though, since it worked before. I did measure it after I pulled it, it was measuring 176 so that seems within range to me(at least not a reading 0).
    Chris
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    Default Re: Looking for understanding on the SSR section of the Renard boards

    Next time that happens try to thoroughly clean the board around the offending triac and optocoupler and then thoroughly dry the board. I'd tend to use iso-propyl alcohol, although others may have alternate suggestions. The boards can accumulate dust and variously substances from the air that can provide leakage paths. But as I said, that's just a conjecture as to what the cause is.
    Phil

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    Default Re: Looking for understanding on the SSR section of the Renard boards

    Interestingly enough, the same situation happened again. I tried doing a thorough cleaning but that didn't fix the issue. I did a quick touch up on the solder joints of the resistor, but that didn't fix it either. To be honest though, in hind sight I did a half baked solder touchup, I didn't clean out the old solder, just added a little more.

    Replacing the resistor worked like a charm so it's really not a big deal, just baffling.
    Chris
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    Default Re: Looking for understanding on the SSR section of the Renard boards

    After removing the resistor is it's condition good enough to consider re-installing it in it's old location? Also, is that channel suck 'ON' before sending data to the controller for the first time after power-on. And is this happening with LED loads, or does it also happen with much heavier incandescent loads?

    I'm still stuck on the idea that it's something other than the resistor going bad that caused the problem. I would have expected a bad resistor to lead to channels that are stuck OFF, not stuck ON. So I'm puzzled as to what's causing this.

    I've talked to Wayne J about similar bad-channel problems that he's encountered, but I don't remember if there was a resolution.
    Phil

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    Default Re: Looking for understanding on the SSR section of the Renard boards

    I'm using a single c7 in this case, and yes, it's stuck on. Even with the opto removed. In both cases I broke the lead off while desoldering. Other than that the resistors look totally fine and even measure to be the correct ohms.

    I'm puzzled too, the dirt theory sounds logical to me but i don't see anything on the boards.
    Again, it's not too big of an issue since it's a simple fix but it is baffling. I do have other channels to fix on a couple of my other older controllers, If I come across the situation again I'll take some pictures and post them.
    Chris
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  8. #8
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    Default Re: Looking for understanding on the SSR section of the Renard boards

    Being stuck ON when the opto is removed really makes me think that it's some sort of contamination on board that is providing a leakage path for current on the surface of the board (could be either top-side or bottom or both).
    Phil

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