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Old 13th October 2009, 06:13 PM   #1
marko is offline marko  United Kingdom
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Default muting relays on outputs...

the below amp is just for referance but i have a similar amp here with the relays and they are not been activated when the amp is powered up, if i bypass them the amp plays fine, what could cause these to fail? and is it safe to bypass them? they do receive 12+ ok but can't figure anything else out

the amp is a genesis sm60..

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Old 13th October 2009, 06:23 PM   #2
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If the relay coils are 12v (some amps use 24v coils) and you read 12v (measured with the probes directly across the relay coil terminals, not referenced to ground) and the relays don't engage, the coils are likely open (not a common failure mode). If the relays engage but pass no audio, the contacts could be damaged/dirty. On single-sided boards, broken solder connections are common but on a double-sided board, they are almost never a problem.

Did you measure the 12v directly across the coil terminals of the relays?

Depending on the protection circuit, it may not be safe to bypass them.

Relays are also used to prevent turn on/off noise. You'd have to bypass them and switch the amp on and off to determine if there was any significant noise.
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Old 13th October 2009, 06:35 PM   #3
marko is offline marko  United Kingdom
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not looked for 12v on the coil but +v defo has 12v going in, wasn't sure what the other terminals did so didn't probe any further, would be easy to tell with the relays removed though! i can't hear them activating although i suspect they are quiet anyway..

i can't find any schematics on the amp either, i could email gordan at genesis, if anyone would have them i'm sure he would!!
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Old 13th October 2009, 06:39 PM   #4
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When you determine which terminals are the coils, confirm that one is at 12v and the other is at 0v (or confirm that you have 12v across the coil terminals).
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Old 13th October 2009, 06:47 PM   #5
marko is offline marko  United Kingdom
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underneath the board there appears to be 4 solder joints on each relay, i'm guessing 2 of those will be speaker connections and other 2 +/-12v to enegize the coils? i'll take a closer look tomorrow...
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Old 13th October 2009, 07:05 PM   #6
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It won't use -12v. It will likely need 12v and ground. If one coil terminal is connected to constant 12v, the other will likely be switched to ground via a transistor.

Look up the numbers on the relay. There should be a datasheet for them. It will tell you what the pin configuration is.
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Old 13th October 2009, 07:33 PM   #7
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I'd be surprised if you can get hold of a schematic.

Seems odd that both relays fail at the same time. To test if they are switching I put my fingers on the case as well as listening for the click. You can, if you are careful, feel the click.
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Old 13th October 2009, 10:39 PM   #8
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I would check the little transistor to the right of the relays, and near the LM op-amp just to the left of the fuse. This would appear to be the protection circuitry. Perhaps the little transistor is the ground switch for the relays...I have seen this sort of circuitry failure stop relays from operating...Just thinking out loud...How ya been Marko ?
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Old 14th October 2009, 04:24 PM   #9
marko is offline marko  United Kingdom
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got it working

whilst having a closer look at the relay terminals i noticed the solder looked a little grey so ran some fresh solder over and it's fixed!! was a dry solder joint in the end.

thanks for all the input guys, much appreciated!
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