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Old 11th January 2013, 10:41 AM   #1
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Default cambridge 840C problem !

my cambridge audio 840C cd player, when switched on after being unplugged over night the right channel plays distorted for about 30 seconds then all of a sudden plays ok i have swapped the cables around and its not the amp ?
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Old 11th January 2013, 11:11 AM   #2
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Thats a strange problem. Have a look at the muting on the analogue output. I've no idea what the player uses, relays, transistor etc but thats where to look. A scope check would show where the problem is in minutes.
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Old 14th January 2013, 03:53 PM   #3
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Default 840C

the right channel works at power up but is faint , then after about 30 seconds the right channel makes a whooshing sound then pops back to full volume .
maybe a dry cap ?
if left on in standby it works fine thats what makes me think a dry cap but the service manual says there are no cap s in signal path ?
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Old 14th January 2013, 04:26 PM   #4
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I've looked at the manual and it appears to use relay muting in a shunt to ground arrangement so I doubt its that tbh.

It needs a scope and a check on the analogue stages. 5 minutes work should show where the problem lies by looking at the output of the opamp signal chain. It's a complex circuit and the manual is spread over many pages so its one of those "where you need it in front of you" in order to make sense of it all and the layout.
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Old 18th February 2013, 08:59 AM   #5
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I had the same problem 1-2 years after I got the player. (But in the left channel)
I started leaving the player on at all time to bypass the problem, but now the noise is there all the time.
I googled the problem and found one guy having the same problem. He sent the player to service, and they changed four capacitators in the power supply. They told him it was a issue with this player, and they changed these capacitators every time they got one of these players in.
I have now dismantled my player and downloaded a service manual. I will try to locate the faulty caps, but I am not shure if my electronics skills will be good enough...

If you get your player repaired, or anyone know which capacitators this is, please tell!
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Old 18th February 2013, 10:09 AM   #6
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Interesting...

The power supply in this player is very "complex", well complex in that it uses many regulated supplies, not complex circuitry.

If it is a PSU issue then I would look at the supplies to the analogue stages and the DAC (for the relevant channel) and perhaps do a quick measure of those supplies when the problem occurs.
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Old 5th November 2013, 10:37 PM   #7
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Default CAMBRIDGE AZUR 840C: Dodgy Chinese capacitors.

Hi Folks,

I'm new to this forum, but would like to seek your advice.

I have a Cambridge AZUR 840CD Player. Nice one , IF it works .

It already had an intermittent problem with the CD (Sanyo) drive, (a couple of years ago), which I repaired by exchanging it for a new one (they are quite cheap ; about 40$.

Now, the player has developed another problem, which seems to be common for this type..

Once switched ON from cold, initially both channels pop & crackle.
One (L) quickly recovers though, and is fine after some 5 minutes.

The other (R) channel stops with popping and crackling, and does not recover but has much reduced output (50% less), some distortion/white noise.
Some 2 months ago, also this channel would recover, but it has deteriorated over time.

The rest of the player is AllRight. Currently I feed the digital output signal into an external DAC (part of TASCAM HS2) and still can enjoy the music.

I heard from the Importer's Service Rep (nice chap) that there are bad capacitors in the DA system / power supplies.

Looking at the schematic, I would like to replace C152, C156, C159, C98 (10 uF NP), left channel and C54, C154, C55, C99 (10uF, NP) Right channel, all around the DA chips.

I read somewhere that the service dpt . of Cambridge replaces some cap's as a matter of course (each time an 840C is brought in).

Are these indeed the offending C's ??

Furthermore, I intend to replace C64/C65 (10u, 35V) DAC1_VA_+5V
C112/C250 (10u, 35V) DAC2_Va_+5V

C46/C137 (100u 35V) +/_ 15V LCH
C104/C105 ditto RCH

C115 10u 35V +5V DAC

C247 10u 35V -5V
C246 ditto -5V(2)

C141 ditto +5V

These are all major C's in the DA converter + OpAmps I can think off.

I do not want to MOD the player ; just fix it

Any more suggestions??


Which Caps should I use?? I intend to at least double the Working Voltage of the CAPS (to 63V) and use Panasonic caps (freely available from CONRAD)..
Will this do the trick in your opinion??

NB I have included the schematic.

http://akdatabase.org/AKview/albums/...0840C%20SM.pdf



Any help is welcome!

Thanks for your support!!

kind regards,

Martin , Holland
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Old 26th November 2013, 02:41 PM   #8
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Default found the dodgy cap

the cap in attached pic was causing the problem
Click the image to open in full size.

Last edited by Mooly; 26th November 2013 at 04:48 PM. Reason: Resized marginsi
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Old 26th November 2013, 04:50 PM   #9
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Well done Faults like that aren't always easy to sus out.
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Old 3rd December 2013, 09:48 PM   #10
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Hi

Thanks for the support.
All 10uF, 50V elco's were changed (by Rubicon) and player is fine again.
Was this due to inherently bad Capacitors (or because the C's are too close to the hot heatsink and get roasted?).
In the latter case , the lay out of the PCB is inherently wrong
NB Also C270 470uF 16V (feeding relais) was replaced.
Regards,

Martin
Click the image to open in full size. Click the image to open in full size.
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