Kicker ZX.750 Cycling in&out of protect mode - diyAudio
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Old 27th May 2012, 07:35 PM   #1
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Default Kicker ZX.750 Cycling in&out of protect mode

I have a Kicker zx750.1 , the amp kicks in and out of protect mode. I brought the amp inside and currently have the cover off the amp and tested with a multimeter the speaker output terminals and this is whats happening. When I power the amp on for the first time it reads 0.0v DC and it begins to clime 0.3, 0.6, 0.10, and so on.. It climes for about 30 seconds until it reaches 1.75v DC and goes into protect mode. It then comes out of protect mode and shoots back up to about 1.45v and climes back up to 1.75v and goes back into protect mode and it just repeats and repeats. Any ideas on it? It does this with or without a subwoofer connected now. Nothing on the board looks bad or smells burnt.
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Old 27th May 2012, 08:00 PM   #2
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With the black probe on the negative speaker terminal and the red probe on either terminal of the output filter inductor, does the voltage spike significantly higher (near 80v)?
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Old 27th May 2012, 09:47 PM   #3
norazmi is offline norazmi  Malaysia
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check the input pre-amp, the problem is there
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Old 28th May 2012, 01:57 AM   #4
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The highest voltage I measured in between the on and off cycles was 5.8V before it kicks back into protect, it looked like it would keep climbing though. And about the input preamp board, the amp still cycles with the board plugged in or not and I still read voltage on the output side. Also noticed that the protect cycles are becoming shorter and shorter so I tested the output voltage again and now I am getting 3-4 volts DC on the outputs. I took notice that two of the transistors are getting warm and the others are cool if you look at the pictures and count form left to right they are numbers 6 & 7 the are the only two different looking ones of the bunch.

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Old 28th May 2012, 03:01 AM   #5
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6 and 7 are regulators and will run hot normally.

Have you checked all of the output transistors to confirm that none are shorted?
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Old 28th May 2012, 03:32 AM   #6
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I wasn't to sure which set to test and what option for ohms my multimeter should be on. Can you tell me which ones from this picture? I think they are the lower left 5 or maybe the first 5 in the top and bottom rows?? Thanks

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Old 28th May 2012, 03:42 AM   #7
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Top and bottom groups of five transistors on the left side in the photo.

With your meter set to ohms, you should not read anything near 0 ohms between the legs of any individual transistor, no matter the placement/orientation of the probes.
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Old 28th May 2012, 03:51 AM   #8
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I just tested both rows with Multimeter set at 20K Ohms and neither combination of pins 1-2, 1-3, 2-3 have a reading of 0. All combinations have ohms pins 1-3 are a steady 50 and the other two combinations increase while I hold the probes on them.
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Old 28th May 2012, 04:08 AM   #9
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Post the DC voltage on all pins of the LM361 (U14). Place the black meter probe on the negative speaker terminal.

Look up the datasheet if you don't know the pin numbering scheme.

Copy and paste the following into your reply.

Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
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Old 28th May 2012, 04:22 AM   #10
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Join Date: May 2012
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LM361

Pin 1: 12.13
Pin 2: 0
Pin 3: 7.58
Pin 4: 0.56
Pin 5: 0
Pin 6: -12.06
Pin 7: 0
Pin 8: 2.95
Pin 9: 1.56
Pin 10: 1.81
Pin 11: 1.59
Pin 12: 0
Pin 13: 2.95
Pin 14:2.95
__________
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