Older QSC Power amp fix. (Random Muting)

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
Just thought I would pass this along. Applies to the 1100, 1200, 1400, 1700 older QSC amps that may randomly mute for a few second to a minute.

Had a 1200 that was driving me nuts as it took about a half hour to start doing it. Turns out that QSC uses an LED soldered in the middle of the pcb (not an indicator) to produce a voltage reference. After enough years, they get flaky and go open circuit at just the right temperature! Had two other amps about the same age, and sure enough with a heat gun and cold spray they were flaky too! 10 cent part, run of the mill LED. Labeled LD3
 
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FMEng

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Fight Leukemia
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Mar 31, 2008
Location
Tacoma, WA
Excellent work on finding that! There is nothing harder to solve than intermittents.
 

Dionysus

Well-Known Member
Joined
Feb 9, 2009
Location
London, Ontario, Canada
Wow, great job and very good to know. Im sure someone will web search this issue and now they will actually find a solution!
Oh the love!

easy fix, great to hear!
 

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
would the PLX series have something like that?
Although I have a PLX, I have not had to rip it apart yet. QSC had a couple of common themes going in their older amps. (Like pulling the speaker output from the power supply and frame grounding the output transistors!) It wouldn't surprise me if they kept doing it. The amps have been rock solid through the years. Outside of a few ring cracks around output transistors, and this problem, haven't needed much attention.
 

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