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Automated Fixtures Dmx input not working

Discussion in 'Lighting and Electrics' started by fredih, Dec 26, 2017.

  1. fredih

    fredih Member

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    Hello everyone,
    I bought some used SGM Idea Spot 575's some time ago, but the DMX input stopped working on one of them.
    Now, I've already checked the wires through, and nothing seems to have blown up on the two control PCB's, so I'm rather clueless as to what would have caused this. Before it was solved by turning off the auto mode, but that didn't work here. Can anyone help me here? I don't want to buy another one...

    EDIT: THere's a few things to say about the fixture:
    The pre-owner installes Powercon In/out, and 3-pin DMX, but as I said everything works just fine.

    Fredi
     
  2. EdSavoie

    EdSavoie Well-Known Member

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    The first thing that comes to mind is the RS-485 transceiver might have gone faulty. Probably a little chip connected directly to the DMX traces.
    (Given that it failed, I'm guessing this device doesn't have an opto-isolator protecting the chip.)

    One thing to note here (for those of you unaware) is that RS-485 is the electrical specification DMX uses to actually transmit data.
     
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  3. fredih

    fredih Member

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    I took out the control board, there's one coil/resistor thingy that looks like it burned out. (https://drive.google.com/open?id=180ArgFB9btPjLFYo4XfrP1Gd8K9TyNYbDA) Maybe that's got something to do with it?
     
  4. fredih

    fredih Member

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    Also, I'm not sure which one's the controller. There's one controller on the board that's replacable without soldering labled GS132N/2U01V10, but I couldn't find anything on Google under that name.
     
  5. Amiers

    Amiers Lighting Phoenix 1 Lamp at a Time

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    Need a different angle. That just looks like someone used that to pry up the board a few times.
     
  6. JD

    JD Well-Known Member

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    That looks like a toasted MOV. Basically a surge suppressor that protects the power supply. Unit will work without it, but it is unprotected from input surges so you should replace it.
    MOVs have a specific lifespan and give a little bit of themselves up each time they clamp a surge. At some point, they have nothing left to give.
    NOTE: Board shown is the power supply board, which is probably not the source of your DMX problem unless it's all on the same board. Follow your DMX line in, it will lead to the RS-485 interface.
     
  7. fredih

    fredih Member

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    eah it's on the same board, but on the other side. I'll try to get a better angle later.
     
  8. DonAllen

    DonAllen Member

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    The GS132N/2U01V10 may be your main controller chip. The most common dmx interface ic is the 75176 in 8 pin dip or surface mount versions. A few manafacturers use an opto isolator instead, but not many. If the 75176 is a dip package soldered direct to the circuit board, I cut the legs off, desolder the ic pins one at a time to minimise damage to the circuit board, fit an 8 pin dip 8 ic socket onto the circuit board, making sure the pin 1 orientation is correct, then plug in the replacement 75176 and hold it in place with a small cable tie.
     
  9. fredih

    fredih Member

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    Alright, I took a few pictures of the two only boards that this device has in its base ( which is where I presume the DMX controller to be; no sense having it in the head).
    https://imgur.com/a/By8QJXz

    I haven't swapped chips between moving heady set because I fear they could blow out, and I don't want a second mover to be dead weight. I also contacted SGM about this, if they still have the chips maybe, but in my experience those kind of requests simply get ignored (Showtec ignored it when I asked for parts).

    The Chip numbers are:

    (The 8-pin on the main board):
    CHN
    LM758N
    KHJ912

    (The other 8-pin on the display board. Both receive the DMX signal from the signal pin. The other ones are labeled with the same sticker.
    9BD07CM
    65LBC184

    Maybe someone here knows anything about the chips mentioned above, maybe one of them is the problem?
     
  10. FMEng

    FMEng Well-Known Member Fight Leukemia

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  11. JD

    JD Well-Known Member

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    That regulator chip (tab package) U6 looks a little toasty.
     
  12. FMEng

    FMEng Well-Known Member Fight Leukemia

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    That's easy enough to check with a voltmeter. Since the unit is otherwise functioning, the regulator is probably fine.
     
  13. JD

    JD Well-Known Member

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    Generally, when something is torn down for service and you see something like that it's a good idea to replace it good or bad. The same thermal degradation you see on those leads coming out of the pack occurs inside the epoxy as well and makes for a future service call. Can't make out the markings but for example LM7805 would be +5 volts, LM7806 would be +6, LM7815 would be 15 volts, The LM79xx are the same but negative voltage. For $1.50 it's cheap insurance.
     
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  14. Chris Pflieger

    Chris Pflieger Active Member

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    I'll disagree. U6 looks fine. Maybe there's a little grease or flux or dirt, but no clear signs of burning or excessive heat. Those LM78xx parts from ST are typically very robust.

    It would be fine to replace it... as long as you don't damage a pad trying to lift it out and remove excess solder, tear a trace, fail to get a good solder joint, neglect to put on enough thermal compound... as least that one has a lock washer and not a rivet, but still...
     
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