Question about Mackie SWA1501 Subwoofer

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Signal light stays on, no sound output

On my Mackie SWA 1501, the speaker pops when powering up, but the signal light remains on even with nothing connected, and when there is something connected, I get no sound. I have checked the 3 internal fuses I can access from just pulling the power amp, but none appear blown. Are there additional fuses under the input board I should check?

My guess from my trouble shooting thus far is I have an input problem... perhaps a blown fuse if there is one under that input board or an ic chip or capacitor on the input may be out... any ideas?

Thanks

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  • MTNKEN Aug 09, 2008

    I have a bit more info now.... I took off the input module, and there is an aluminum strip on the side of the board that is screwed into two chips mounted off of the input board... these chips are connected by three soldered legs into the input board, and one of those chips is completely disconnected from the assembly... the chip is in the T14 slot.... and has TIP122 C0420 written on it.... it is located on the lower left corner of the input board...



    I tried moving it to establish a connection while the unit was plugged in, and the speaker popped slightly

  • TheShards Feb 14, 2009

    I, too, had this same problem with my sub. Fortunately I have two of them, so I was able to swap the power amp stages to troubleshoot the speaker vs. amp. I did notice the T1L250V fuse had blown but replacing it did not fix the problem (of course, fuses mostly blow because they were taken down by an active component). In desperation (because I dreaded paying upwards around 500 bucks to replace the amp, and so far I was only down 50 cents for the fuse) I took off the input stage and found exactly the same result: One of the transistors was COMPLETELY broken from its connection. The three legs broke right at the board solder joint (i.e., the solder welds held fine, but the actual metal legs broke). There was no way I could solder the transistor onto the existing stumps, so I removed the stumps and soldered three long legs that I cut off from a wirewrap IC socket I had laying around and then soldered then into the holes on the pc board. Then I soldered the the transistor stumps onto those new legs sticking out of the board taking care to make sure the holes on both transistors lined up with the heat sink strip (I had to remove a small portion of the glue melt that hold the strip firmly to the board soI could get to the transistor's mounting holes on the board; no big deal though). Now the cabinet seems to work fine. I have a gig in a few days so I can't wait to see if it still craps out after a half hour or really does go the distance now. But after only 50 cents...and a couple of hours 'rediscovering the wheel'...it feels good to know the research on the web paid off, even if only temporarily! Thanks for your help folks! This was quite the adventure. -Phil.

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T14 is part of the +15v power supply that feeds the input board.
It is actually a transistor.
If this is the only problem on the board, then this transistor could be resoldered back on but you will have to make sure it tests OK and it attaches to the heatsink the same way it came off. ie make sure it is electrically isolated from the heatsink
It seems if there is no fuses blown on the power amp board you might be one of the lucky ones.
In my opinion this amp is a clever design but is under-engineered for robustness

Posted on Sep 16, 2008

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