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crown cts 1200 pip-bby amp hum and clip

cts 1200 hum clip constant

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#1 wolff46

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Posted 25 May 2014 - 04:30 PM

I have a crown cts 1200 that when it is powered with no input, and with one 8 ohm speaker connected to either ch 1 ch2 or bridged I get a steady level hum, like a ground loop.  Also the ch 2 clip light will come on and stay lit.  Sometimes giving it a firm tap will blink the clip light out . Any suggestions on troubleshooting? I have the board out and have inspected solders as best I could. Have a multimeter as my only diagnostic device

#2 joust

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Posted 26 May 2014 - 02:06 PM

Hi,

Check and replace C933 (change from a 470UF to a 560UF 35V).
Also, check U22 regulator (+15V reg, 7815) under Ch2 silpad. The input to the regulator should be around +18V.

Alain

#3 wolff46

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Posted 28 May 2014 - 07:30 PM

Only getting 14.92 on u22.

#4 joust

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Posted 30 May 2014 - 02:34 PM

Is 14.92V on the input or the output side? If it is on the output side then the regulator appears to work fine. If, on the other hand, this voltage is the input voltage to the regulatopr, then we have a problem! Can you do major troubleshooting? You mention you have only a multimeter... If at all possible I would send the amp to our favorite Crown authorized service center. You will need to remove the main board from the chassis and probably have to do some unsoldering. Have you checked and measured C933?

Alain

#5 wolff46

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Posted 22 June 2014 - 03:03 PM

I'm not sure which side it was on. Ordered the parts should have them replaced tomorrow. Will let you know how that goes. Thanks again for your help.

#6 wolff46

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Posted 26 June 2014 - 06:58 PM

Replaced the voltage regulator (got a 56 uf cap instead of a 560 so put the old one back in) now I'm just getting a thermal warning

#7 joust

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Posted 27 June 2014 - 10:13 AM

Get the 560UF/35V! It makes the whole difference! :)

A.