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Thread: M-Audio powered speaker turn on problem

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    M-Audio powered speaker turn on problem

    Have a pair of M-Audio GSR10 powered PA speakers. They refuse to turn on with power switch, but when I ramp them up on the variac they come on normally and work correctly. Any suggestions why?

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    It is really strange that two devices have the same fault.
    The easiest way is to turn on the device through the variac and to measure the voltages at several points at
    the input of the power source and inside. Then turn it on without variac and see what voltages have changed.
    Analyze and try to find the cause. It may take several attempts. The task is complicated by the fact that the
    type of the power source is SMPSU.

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    Lifetime Member Enzo's Avatar
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    Many SMPS have a soft start, like a low resistance with a shorting relay. Possible that using the variac fools the soft start circuit.

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    Education is what you're left with after you have forgotten what you have learned.

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    This SMPSU uses NTC, not shorting relay.

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    Lifetime Member Enzo's Avatar
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    NTC is another way to do it, yes, but I have rebuilt enough Behringer SMPS with a relay shunting resistors in that function. We don't seem to have a schematic here, so I believe you, but we are limited in the help we can supply.

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by Enzo View Post
    NTC is another way to do it, yes, but I have rebuilt enough Behringer SMPS with a relay shunting resistors in that function. We don't seem to have a schematic here, so I believe you, but we are limited in the help we can supply.
    A timing issue? variac bringing it up slowly?

    Check to see if there are any part numbers on the board sometimes we can find schematics based on those.

    nosaj

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    Click image for larger version. 

Name:	IMG_20190616_133918X.jpg 
Views:	24 
Size:	805.2 KB 
ID:	53998

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    I ordered new thermistors used for inrush current limiting hoping that will solve the problem
    Keep ya all posted

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by Bigdrums View Post
    Click image for larger version. 

Name:	IMG_20190616_133918X.jpg 
Views:	24 
Size:	805.2 KB 
ID:	53998
    Does board look similar to this?

    https://www.fullcompass.com/prod/238...ply-pcb-for-k8
    nosaj

    If so maybe this will help
    http://bee.mif.pg.gda.pl/ciasteczkow...Schematics.pdf

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    I inserted the wrong pic, here are 2 of the M Audio board:

    Click image for larger version. 

Name:	IMG_20190616_135457X.jpg 
Views:	28 
Size:	1.32 MB 
ID:	54001Click image for larger version. 

Name:	IMG_20190616_135445X.jpg 
Views:	30 
Size:	1.64 MB 
ID:	54002

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    Old Timer J M Fahey's Avatar
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    I guess "not using a Variac" does not imply "using a lightbulb limiter instead"
    Just checking.

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    Juan Manuel Fahey

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    Hey Juan:
    You suggested for me to draw a schematic of the Furman Parametric EQ I was working on which I did and posted it.
    But I did not hear back from you on it. Could you take a look and see what you might comment on ?
    Thanks

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    Well the thermistors don't help. I have noticed a relay in the PS section that engages when I ramp up slowly, and takes about 5 seconds or so to disengage when the power is cut. If I turn the power back on before the relay disengages, the amp comes up fine. So what ever it is has to do with that relay engaging. Why it doesn't engage when the power is just turned on I have no clue. Anyone?

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    Old Timer olddawg's Avatar
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    Are you monitoring the voltage on the relay? A common problem with protection relays is the contacts “carbon up” and become resistive, arc, or stick.

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    Quote Originally Posted by olddawg View Post
    Are you monitoring the voltage on the relay? A common problem with protection relays is the contacts “carbon up” and become resistive, arc, or stick.
    The 12v activating the relay is present only when I ramp the power up somewhat slowly on the variac

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    Supporting Member Jazz P Bass's Avatar
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    It looks like it would be a real PITA, but could you possibly trace where the 12Vdc for the relay is coming from.
    It sounds to me like a timing capacitor issue.

    A lot of these 'pack em smaller' type units have some real boo boos when it comes to component layout.

    Like placing electrolytic timing capacitors next to heat sources.

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    I followed the relay traces to a 100uf 16v electrolytic that checked good.
    I tried turning on the unit without the electrolytic in place and SOG it turned on, no variac but light bulb limiter in line
    I remove the light bulb limiter and it won't turn on.
    Is that maybe because the bulb is slowing the current in-rush?

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  18. #18
    Supporting Member Jazz P Bass's Avatar
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    I would ditch the limiter.

    What circuit does the 100uf/ 16V cap attach to?
    In other words, what turns on the relay?

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    Last edited by Jazz P Bass; 07-04-2019 at 04:17 PM. Reason: punctuation

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    Very difficult to say what turns on the relay. Its a double sided board, small traces disappearing under various components. I'm wondering what risk there might be by just jumpering the relay since that seems to be where the issue is? I don't know for sure it would work but I think it might. The relay I'm referring to is just before the rectifier.

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    Don't forget the joker g1's Avatar
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    It will work but you will lose the protection if there is a malfunction.

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    Old Timer J M Fahey's Avatar
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    I would bypass the relay with an NTC thermistor and check whether it now turns on.

    Use an inrush current limiting thermistor pulled from an old unused PS smps.
    This is just for testing, you may laterreplaced the "borrowed" NTC where it belongs.

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    Juan Manuel Fahey

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    The thermistor worked perfectly! Thanks
    What does NTC stand for?

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    Supporting Member The Dude's Avatar
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    Negative temperature coefficient.

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