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Creast CA9 Fault

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100 Volt-line View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 100 Volt-line Quote  Post ReplyReply Direct Link To This Post Topic: Creast CA9 Fault
    Posted: 20 October 2011 at 12:16pm
One for you amp repairers..........

Crest CA9 MK2 has a fault on left channel,the problem is it is very quiet. There is sound there, but it is quiet. The other side works fine.

My first thoughts were towards a sticky selector switch for the bridge/parallel/stereo switch, but working this a few times has not remedied it. The fault persists in stereo and parallel mode, not tried bridge. Its not dodgy cables or anything, tried all that, the only thing that has happened recently is the fan on the faulty side jammed when I lent it to a mate for his disco. It went into protect (as it would) and was ok when it cooled down, so he says !  this happened a few times apparently, and him not being technical, never thuoght to un-jam the fan, or ring me !  Could this have done some damage ?

My background is electrical not electronics, so i can get so far with fault finding, but am not too good with the real technical stuff. (bias voltages, bi polar transistors, negative feedback...all Chinese to me )I have a scope, but have never used it !

This amp has had very little use; more time stood than being used, that said, its never ever been faulty before.


Any thoughts are appreciated.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote inge_am Quote  Post ReplyReply Direct Link To This Post Posted: 20 October 2011 at 9:27pm
Hi,

the sound of defective channel is only quiter or distorted too?
Is it full bandwidth or with less low frequencies?


Let me know.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote 100 Volt-line Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2011 at 9:04am
Hello


It is just quieter, sounds full range.  It just sounds like one side is turned down a lot, I have tried the input attenuator, and turning that down makes it even quieter (as it would). The signal LED barely flashes for this channel.

Its probbably something simple !
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Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2011 at 9:18am
Compare the attenuation voltages on IC4, pins 7 and 10.

If the same, try replacing IC4, a NE5517D attenuator.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pinyorouk Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2011 at 9:21am
Hi,

Sounds like there is a fault in the input section of the amp. Could be the input volume control or one of the components in the low level circuitry of the amplifier. Best bet would be to send it off to repair. If you were to semi dismantle it and accidentaly caused a short circuit the repair bill may quickly soar. Had you have had electronic experience I would have suggested that you use a signal generator and oscilloscope to trace the signal through the amplifier circuit starting from the input. As _DKJ_ mentioned, you could do a comparison of the correctly working amps signal levels at different points in the circuit.
Originally posted by 100 Volt-line 100 Volt-line wrote:



Hello


It is just quieter, sounds full range.  It just sounds like one side is turned down a lot, I have tried the input attenuator, and turning that down makes it even quieter (as it would). The signal LED barely flashes for this channel.

Its probbably something simple !


Edited by Pinyorouk - 21 October 2011 at 9:37am
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100 Volt-line View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 100 Volt-line Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2011 at 4:14pm
With a bit of swapping around, I have located the fault to the board that piggy backs the main board on the faulty channel.  Thats about as far as I can go, so it looks like it needs to go for repair. I used to go to Audio Labs in Leeds, but they have retired and shut up shop, anyone know anywhere else in Yorkshire ?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote service dept Steve Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2011 at 7:08pm
I was going to suggest that you check the pre-amp boards (the ones you mentioned) because the favorite failure of these amps is that the connector partly disconnects leading to unpredictable behavior, I assume that you have swapped both boards and the fault has changed sides?  
We are not "They", We are "The others"http://www.servicedept.co.uk -
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 100 Volt-line Quote  Post ReplyReply Direct Link To This Post Posted: 22 October 2011 at 10:19am
Yes, thats right.  I gave the pins a clean up just in case. Looks like its a repair job !
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Post Options Post Options   Thanks (0) Thanks(0)   Quote service dept Steve Quote  Post ReplyReply Direct Link To This Post Posted: 23 October 2011 at 10:48am
But you have swapped the boards and now the fault is on the other channel, right?
We are not "They", We are "The others"http://www.servicedept.co.uk -
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 100 Volt-line Quote  Post ReplyReply Direct Link To This Post Posted: 24 October 2011 at 11:58am
Yes I have
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Post Options Post Options   Thanks (0) Thanks(0)   Quote G-Wakefield Quote  Post ReplyReply Direct Link To This Post Posted: 01 November 2011 at 12:59pm
Abacus Electronics have taken up work from Audio Lab
 
 
Give him a call before turning up as he works from a garage at home and sometimes doesn't have room, may give you a day to drop off!!
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