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Old Jun 11, 2015, 12:10 AM
RcPro97 is offline
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Car audio amp problem

Hi everyone. I bought a broken car amp in hopes that I could fix it and get it going again. The guy I bought it off said that it suddenly stopped working. The amp is a soundmagus Q-150, 4X150Wrms.



It powers up, as normal. The power light comes on, and then the protection light turns off about a second later. I only have 2 speakers at the moment to test it, so I am bridging it to make it 2 channel. I hooked 2 speakers to it and one just hisses, and the other makes a ticking like a clock. When I try powering it with only 1 speaker connected it just 'ticks', no matter what channel it is connected to.

I measured the voltage of the power supply and it gives a steady 32V and -32V, which is exactly what I would have expected. The voltage does not drop when speakers are connected and it is trying to play.


One of the 3300uf caps on the power supply was a bit swollen, so I replaced it with a 4700uf, because that's what my electronics store had available. I will get the right size eventually. But I figured that it would not matter on the power supply for testing.

I have taken all of the audio transistors off the board and tested them individually. They all appear to be in good shape, they are behaving exactly as I expected.

I also measured the voltage to the microcontroller, which measured 6V.

The last thing I can think of is if something is wrong with the section which takes the input signal, works out the output and supplies this to the transistors. Obviously this is going to be a bit harder to test. I'm wondering weather someone else who might know a bit more about this than me could suggest what It could be. Weather anyone has had a similar problem?

Thanks
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Old Jun 14, 2015, 01:13 PM
Peacemakr40 is offline
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Your best bet would be to get a signal generator to feed each of the inputs and a scope to track the signals. You can also check the DC rails to see if you're getting any deviations or excessive noise. I would guess that since you haven't popped any fuses that your output section is still ok. Get 4 - 8 ohm 50 watt power resistors for your outputs. This way you can isolate channels. If you have a bad component in your protection circuit, it will cause similar symptoms.
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Old Jun 16, 2015, 08:53 AM
Xfactor940 is offline
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you can find a generator program for the pc and feed the inputs off the pc's sound card using a 1/8 stereo to rca adapter. But you need a scope to verify your generators output and amplitude.
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Last edited by Xfactor940; Jun 16, 2015 at 08:58 AM.
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Old Jun 16, 2015, 08:59 AM
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you can find a generator program for the pc and feed the inputs off the pc's sound card using a 1/8 stereo to rca adapter. But you need a scope to verify your generators output and amplitude before u troubleshoot.
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