Momentary Switches Distribution Board

Discussion in 'The Projects Forum' started by steward, Jul 24, 2011.

  1. steward

    Thread Starter Active Member

    Jan 21, 2011
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    My fellow electrical-electronic slueths,

    Back in January I started a thread which could have been a potential solution for described needed functions on a brand new printed circuit board. I am hoping that you can have that open in a separate window as a reference.

    http://forum.allaboutcircuits.com/showthread.php?t=48762

    The reason for the new post is there is another approach to the solution to our problem. Hopefully I can get input with this post on the possibility of repairing an existing board that has all the functions I need --- described in the above January post. The company that sold me the board back in 1987 say that is was made by another company that they don't remember. Hopefully, with the below link to pictures of the board you folks can help me pick out a broad enough range of a triac that the odds of success will be greater. I am thinking that the only component that can cause "an output & its corresponding LED to stay on" ---- even at start up --- would be a triac that finally fused or whatever. Another thing that complicates this process is the fact that the board was sprayed with a waterproofing clear coat. Anybody have experience with replacing a triac on a board that had waterproofing spray? I do have a temperature controlled grounded tip lab grade soldering station if that helps. Notice the small black components that are parallel to the specific LEDs in the pictures on the following public link. The black components (triacs?) have the following printed on them: R P1 0181 ECB if that helps to find suitable replacement triacs. Since 7 of the 10 boards that I have --- have been working perfectly with continuous use since 1987 it shows that the board was reasonably well made & could last for another 24 years it seems --- especially with a proper hopefully minor triac replacement repair on rare occasions.

    http://www.mediafire.com/kingkoinmike#1mct4rf78mm5x,1

    It would be a shame if we can't solve this problem because this distribution board allows us to have a much more user friendly interface with our self service car wash users than the much more common less friendly triple deck rotary switches. This board or a similar board like Ken Moffett almost made back in January --- allows for the users to see that the latched on selection & output is lit up when selection is made & it allows for 12 IP69 vandal resistant momentary buttons. I've already bought well over a hundred of the spendy stainless button switches from Digikey last fall --- so I am plenty nervous about making this work without too much delay! Thanks for any assistance or suggestions & I will do my best to reciprocate in as good a faith way as possible!

    Mike
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    I think it's more likely that the component you are talking about is a transistor. The "ECB" would mean emitter collector base.
    I'd assume that this a LED driving transistor, where the driving signal comes from one of the ICs on the board.

    So it could be the transistor, as you said, even though I found it more likely to be the IC where the driver signal comes from...

    The transistor (if it is one) you could simply test with a multimeter diode tester (although I'm not sure about the model of the "transistor", the "R P1 0181" doesn't mean anything to me).

    If it's not this component that is defective you'll have to follow the traces to see from which IC it's being driven, find it's datasheet and verify if it fulfills its function.

    Well, and if the component is a triac forget everything I wrote. :D
     
  3. steward

    Thread Starter Active Member

    Jan 21, 2011
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    Thanks for responding Praondevou --- hopefully others can further the dialog with valuable information that will help to avoid a waste of these boards & also the waste of my over 100 brand new momentary switches etc. & a ton of other work customizing the faceplates that is already done. I was banking on the boards not developing this "output & LED stuck on condition" consequently possibly making me run out of boards & forcing me to go with the less user friendly triple deck rotary switches.

    I added 5 more higher resolution pictures with a macro lens to the following public site:

    http://www.mediafire.com/kingkoinmike#1mct4rf78mm5x,1

    Hopefully, we all will gain a better understanding of what the components are & what they are doing from some of you. Since the board has not been in production for over 20 years it is very unlikely there would be any reverse engineering issues --- especially if the goal of looking at it is to mainly just repair the dang thing! Improving our understanding is also of value too!

    The board is a quite a bit more complicated than what Ken & the others were suggesting if we started from scratch --- but I would hope after 24 years the technology has improved that would accomplish the same objective via the mosfets or whatever!

    Mike
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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  5. steward

    Thread Starter Active Member

    Jan 21, 2011
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    Praondevou & others,

    Thanks. The picture of the new 2N5172 comes up looking exactly like those black components parallel to the LEDs. Newark has over 5,000 of them. Now to figure out the best way to gingerly take the suspect component off of the clear coated waterproofed board & test it like you said. I will have to look at my 2 multimeters (one is a Fluke 12) & my dedicated diode tester to see if I have the ability & enough smarts to verify the transistor failure etc.

    I would think the 2N5172 is mainly for the corresponding LED. If one of those 12 transistors did fail --- I suppose the leak through or whatever could cause the corresponding output to also be stuck. I know if the board would get totally drenched with water --- we would let it dry out & that same symptom of a stuck output & LED would clear up.

    I did look at your arrow on the return pic crop & note: That turned out to be light (glare) reflecting --- it played a trick on the camera.

    I will try to take baby steps to resolve this --- but if the 2N5172 replacements don't work --- I hope someone can make an intelligent guess to what the next most likely component could cause a stuck output or even 2 stuck outputs.

    I am kind of squirming as to the "triac" bad info --- but that is what I was told by 2 so called experts after they specifically looked right at the board. One of the experts was in charge of the department that sold many of the much too quickly discontinued boards.

    Mike
     
  6. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Well, they still may be right, they had the PCB in front of them.:)

    But from the description you gave this component doesn't look like a triac.
    Also, have a look where the base of this transistor is connected to.
     
  7. steward

    Thread Starter Active Member

    Jan 21, 2011
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    Praondevou, Ken Moffett & others,

    I am guessing to some extent but it seems like the two 8 circuit MM74C373N latching chips seem like the next potential components that could cause that specific problem. They are still available if I need try one of those. There are some Schmitt Triggers ??? on the board. Some MC14001U NOR gates??? There is a M8712 LM 2903N on the board that appears to be a dc/dc converter. The rest of the parts are lots of resistors, diodes, & capacitors which I suppose are all needed for one reason or another but it does not seem that they would cause the output & LED stuck on symptom. Unless one of those failing would cause a domino effect. No where on any failing board is there a sign of burn or overheating so --- no clues there!

    You said: "Also, have a look where the base of this transistor is connected to" I will have to study that more with the lighted magnifier on the workbench but it does appear to loop around to a MM74C373N latching chip.

    Anybody have experience with desoldering & resoldering components on a board that has a clear waterproofing coating? I might have to start a new post on that question or do a search it seems.

    It would be nice to get some comments on this 1987 existing board's approach vs the general design that the responders on the
    http://forum.allaboutcircuits.com/sh...ad.php?t=48762 had in mind for the latching & the "only one 24VAC output on at a time" condition etc.

    Mike
     
  8. #12

    Expert

    Nov 30, 2010
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    I use xylene or toluene (or xylol or toluol) to remove conformal coatings.
     
  9. steward

    Thread Starter Active Member

    Jan 21, 2011
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    #12,

    Thanks, is this something that I can get a can of --- at Walmart or Ace Hardware or any paint store? Where can I buy a small amount conformal waterproofing coating once I have the new components soldered in?

    I wish there was simple way to test the MM74C373N. I suppose while the board is live with power I might be able to needle through to see with a voltage meter if the output problem is on the trace from the MM74C373N on the specific trace leading to the specific problem output. I wonder if that would be too risky possibly taking out more components unless the digital Fluke 12 multimeter only measures the power & does not introduce any on the board???

    Mike
     
  10. steward

    Thread Starter Active Member

    Jan 21, 2011
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    0
    Based on the information on the above posts within this thread --- can anyone suggest a possible shop in the USA or Canada that would take on the repair of it? I am located in Bismarck, ND & have a UPS account so I could potentially ship it wherever. I am almost positive that none of the components are completely obsolete. I have pretty much exhausted any possibility of finding the original OEM or any component level documentation.

    mike walsh king koin of bismarck
     
  11. #12

    Expert

    Nov 30, 2010
    16,343
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    Those solvents are common at home improvement stores.
    Another way to get through conformal coatings is to get a probe with replacable tip and replace the tip with a sharpened allen wrench. Being made of tool steel, they poke very well.

    I'm sure that people who actually know about conformal coatings will have a stroke when they read this but, I use Krylon crystal clear acrylic spray paint as a circuit board coating. It also keeps the roaches from eating the labels in equipment that lives outdoors, for a few years.
     
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