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Crown Com-Tech 400 Dead Channel?
Old 5th September 2011
  #1
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Crown Com-Tech 400 Dead Channel?

I just purchased a used Crown Com-tech 400 amplifier and after hooking up 2 JBL HSL410's (that work), I noticed that channel 1 is pretty much dead. I am getting a small bit of noise out of the speaker on channel 1 when I play music, however it is barely noticeable and garbled.

I hooked up my equipment in this order:

Computer (Creative X-Fi Titanium)->Com-tech 400->(HSL410's/ Jamo Sub 250- in parallel)

Note that my Jamo Sub has line-level inputs for amps that do not have a sub out. I have tried disconnecting the sub and reversing the polarity on the speaker wires on channel 1 to no avail.

My regular powered computer speakers also work well so this can't be an issue with my sound card. I also double-checked all of the input and output wiring on the amp. I originally had the input wiring connected incorrectly (positive in + and negative in the ground terminal), however I fixed the wiring when I moved the negative wires over to the (-) input terminals of the amp.

I am using regular Radioshack Megacable speaker cable by the way. Please let me know if I am missing any information.

What is the most likely cause of this problem? I don't mind opening up the amp and replacing components, however I am having difficulty finding where to start.

Also, please let me know if I should replace anything (like op-amps) while working on the amp to improve sound quality on both channels.

Thanks for the help.
Old 6th September 2011
  #2
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I know that bumping threads is frowned upon in many places, however I decided to disassemble my amp and noticed a blown resistor...



Do you think that I should just replace this resistor and try to power up my amp again or do you think that there might be more serious problems like broken capacitors? I checked for leaking capacitors and didn't see anything.

Also, I checked the Schematic from Crown and noticed that this resistor (R701) is on the power control board. Please see page two on the following pdf:

http://www.crownaudio.com/pdf/legacy/ct400_main.pdf

Thanks!
Attached Thumbnails
Crown Com-Tech 400 Dead Channel?-blown-r701.jpg  

Last edited by techbiker; 6th September 2011 at 12:21 AM.. Reason: Power Control Board!
Old 6th September 2011
  #3
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MIKEHARRIS's Avatar
Crown service is very good...they often repair non warranty amps at no charge

Often more damage occurs in shipping...make sure is double boxed
Old 6th September 2011
  #4
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ddageek's Avatar
 

Check that the the Bridge, Dual ,parallel switch is set to dual. Are both transformer switches se for 8/4 ohms? Both level controls up?
Old 7th September 2011
  #5
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Quote:
Originally Posted by MIKEHARRIS View Post
Crown service is very good...they often repair non warranty amps at no charge

Often more damage occurs in shipping...make sure is double boxed
Thanks for the suggestions but I called up Crown and they have outsourced service for their older systems to another company that charges $75 an hour for service. At that price, I'm going to try to diagnose the problem myself. I guess that Crown still offers free phone support so they can walk me through diagnostic procedures to make sure that everything is working.
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